diff --git a/appveyor.yml b/appveyor.yml
index 40dafad..9c3a1e2 100644
--- a/appveyor.yml
+++ b/appveyor.yml
@@ -29,8 +29,8 @@ test_script:
       ln -s /lib/libc.musl-x86_64.so.1 /lib64/ld-linux-x86-64.so.2
       chmod -R 777 /appveyor/projects
       npm install
-      npm test
-      npm run test:integration
+      npm run test -- --ignore-only
+      npm run test:integration -- --ignore-only
 
 artifacts:
   - path: ./*_sc-core.7z
@@ -38,7 +38,9 @@ artifacts:
 # on successful build
 on_success:
   - sh: |
-      apk add curl jq
+      if [ ! apk add curl jq ]; then
+        exit 1
+      fi
       CURR_VER=$(cat package.json | jq -r .version)
       if curl -s -X GET -H "Authorization: token $deploytoken" https://git.nfp.is/api/v1/repos/$APPVEYOR_REPO_NAME/releases | grep -o "\"name\"\:\"v${CURR_VER}\"" > /dev/null; then
         echo "Release already exists, nothing to do.";
diff --git a/core/application.mjs b/core/application.mjs
index 80d46a6..f3ddbe2 100644
--- a/core/application.mjs
+++ b/core/application.mjs
@@ -1,4 +1,6 @@
 import { EventEmitter } from 'events'
+import cluster from 'cluster'
+
 import fs from 'fs/promises'
 import { request } from './client.mjs'
 import HttpServer from './http.mjs'
@@ -21,6 +23,7 @@ export default class Application extends EventEmitter {
     this.http = new HttpServer(this.config)
     this.module = null
     this.running = false
+    this.workers = {}
 
     // Fresh is used to indicate that when we run the application and it fails,
     // whether the environment we are in was fresh or not. An example would be
@@ -38,18 +41,34 @@ export default class Application extends EventEmitter {
     this.config.heartbeatAttempts = this.config.heartbeatAttempts || 5
     this.config.heartbeatAttemptsWait = this.config.heartbeatAttemptsWait || (2 * 1000)
     this.config.heartbeatPath = this.config.heartbeatPath || '/'
+    this.config.clusterWaitOnCrash = this.config.clusterWaitOnCrash || (1 * 1000)
 
     Object.assign(this, {
       setInterval: opts.setInterval || setInterval,
+      setTimeout: opts.setTimeout || setTimeout,
       fs: opts.fs || fs,
+      cluster: opts.cluster || cluster
     })
 
+    this.isSlave = this.cluster.isWorker
+    this.monitoringCluster = false
+
+    if (this.config.cluster && !this.isSlave) {
+      for (let i = 1; i <= this.config.cluster; i++) {
+        this.workers[i] = null
+      }
+    }
+
     this.ctx.db.addApplication(name)
   }
 
   startAutoupdater() {
     if (this.provider.static) return
     if (this.config.updateEvery === 0) return
+    if (this.isSlave) {
+      this.ctx.log.warn('app.startAutoupdater was called from within a slave')
+      return
+    }
 
     let timer = this.setInterval(() => {
       this.update().then(
@@ -64,15 +83,19 @@ export default class Application extends EventEmitter {
     timer.unref()
   }
 
-  updateLog(message) {
+  updateLog(message, level = 'info') {
     this.ctx.db.data.core[this.name].updater += message
-    this.ctx.log.info(message)
+    this.ctx.log[level](message)
     return message
   }
 
   msgStatic = 'Provider in question is static and so no update required, nothing to do.'
 
   update() {
+    if (this.isSlave) {
+      this.ctx.log.warn('app.update was called from within a slave')
+      return null
+    }
     if (this.provider.static) {
       if (this.ctx.db.data.core[this.name].updater !== this.msgStatic) {
         this.ctx.db.data.core[this.name].updater = ''
@@ -122,18 +145,19 @@ export default class Application extends EventEmitter {
     let latest = null
 
     try {
-      log += this.updateLog(`Checking for latest version at ${new Date().toISOString().replace('T', ' ').split('.')[0]}. `) + '\n'
+      log += this.updateLog(`Checking for latest version at ${new Date().toISOString().replace('T', ' ').split('.')[0]}. `, 'debug') + '\n'
 
       // Get the latest version from our provider
       latest = await this.provider.getLatestVersion()
 
-      log += this.updateLog(`Found ${latest.version}. `) + '\n'
-
       // If the versino matches the latest installed, then there's nothing to do
       if (this.ctx.db.data.core[this.name].latestInstalled === latest.version) {
-        this.updateLog('Already up to date, nothing to do. ')
+        log += this.updateLog(`Found ${latest.version}. `, 'debug') + '\n'
+        this.updateLog('Already up to date, nothing to do. ', 'debug')
         return null
       }
+
+      log += this.updateLog(`Found new update ${latest.version}. `) + '\n'
       
       // Make the id for the vesion the version number. Allows for easy lookup
       // among other nice and simple structure.
@@ -241,7 +265,7 @@ export default class Application extends EventEmitter {
         // For some weird reason, --loglevel=notice is required otherwise
         // we get practically zero log output.
         await this.ctx.util.runCommand(
-          'npm.cmd',
+          this.ctx.util.getNpmExecutable(),
           ['install', '--production', '--no-optional', '--no-package-lock', '--no-audit', '--loglevel=notice'],
           folder,
           function(msg) { log += msg }
@@ -291,56 +315,128 @@ export default class Application extends EventEmitter {
     this.module = module
   }
 
+  workerDied(worker) {
+    if (this.workers[worker.w_id] !== worker) {
+      return
+    }
+    this.workers[worker.w_id] = null
+
+    this.setTimeout(() => {
+      if (this.workers[worker.w_id]) return 
+      this.startForkProcess(worker.w_id, this.ctx.db.data.core[this.name].active)
+    }, this.clusterWaitOnCrash)
+  }
+
+  startForkProcess(i, version) {
+    this.workers[i] = this.cluster.fork({
+      CLUSTER_APP_NAME: this.name,
+      CLUSTER_APP_VERSION: version,
+      CLUSTER_APP_INDEX: i,
+    })
+    let pid = this.workers[i].process.pid
+    this.ctx.log.info(`Creating worker ${i} (${pid})`)
+    // this.workers[i].once('listening', () => {
+    //   this.ctx.log.info(`Fork ${i} is alive and listening`)
+    // })
+    this.workers[i].once('exit', (code, signal) => {
+      if (signal) {
+        // this.ctx.log.info(`Worker ${i} (${pid}) was killed by signal ${signal}`)
+      } else if (code !== 0) {
+        this.ctx.log.warn(`Worker ${i} (${pid}) exited with code ${code}`)
+      }
+    })
+    this.workers[i].w_id = i
+    this.workers[i].listening = false
+    this.workers[i].started = new Date()
+  }
+
   async runVersion(version) {
     this.ctx.db.data.core[this.name].active = version
     await this.ctx.db.write()
 
-    if (version !== 'static') {
-      let indexPath = this.ctx.util.getPathFromRoot(`./${this.name}/${version}/index.mjs`)
-      await this.fs.stat(indexPath).catch((err) => {
-        return Promise.reject(new Error(`Version was missing index.mjs: ${err.message}`))
+    if (this.config.cluster && !this.isSlave) {
+      for (let i = 1; i <= this.config.cluster; i++) {
+        this.startForkProcess(i, version)
+      }
+    } else {
+      if (version !== 'static') {
+        let indexPath = this.ctx.util.getPathFromRoot(`./${this.name}/${version}/index.mjs`)
+        await this.fs.stat(indexPath).catch((err) => {
+          return Promise.reject(new Error(`Version was missing index.mjs: ${err.message}`))
+        })
+
+        this.fresh = false
+        let module = await import(this.ctx.util.getUrlFromRoot(`./${this.name}/${version}/index.mjs`))
+        this.registerModule(module, version)
+      } else {
+        this.fresh = false
+      }
+
+      let errTimeout = new Error(`Version timed out (took over ${this.config.startWaitUntilFail}ms) while running start()`)
+
+      await new Promise((res, rej) => {
+        setTimeout(() => {
+          rej(errTimeout)
+        }, this.config.startWaitUntilFail)
+
+        let startRes = this.module.start(this.http, this.config.port, this.ctx)
+        if (startRes && startRes.then) {
+          return startRes.then(res, rej)
+        }
+        res()
       })
 
-      this.fresh = false
-      let module = await import(this.ctx.util.getUrlFromRoot(`./${this.name}/${version}/index.mjs`))
-      this.registerModule(module, version)
-    } else {
-      this.fresh = false
+      if (!this.http.active) {
+        return Promise.reject(new Error(`Version did not call http.createServer()`))
+      }
     }
 
-    let errTimeout = new Error(`Version timed out (took over ${this.config.startWaitUntilFail}ms) while running start()`)
-
-    await new Promise((res, rej) => {
-      setTimeout(() => {
-        rej(errTimeout)
-      }, this.config.startWaitUntilFail)
-
-      let startRes = this.module.start(this.http, this.config.port, this.ctx)
-      if (startRes && startRes.then) {
-        return startRes.then(res, rej)
-      }
-      res()
-    })
-
-    if (!this.http.active) {
-      return Promise.reject(new Error(`Version did not call http.createServer()`))
+    if (this.isSlave) {
+      return
     }
 
     let lastErr = null
 
     for (let i = 0; i < this.config.heartbeatAttempts; i++) {
       try {
-        await request({ timeout: this.config.heartbeatAttemptsWait }, `http://localhost:${this.config.port}` + this.config.heartbeatPath, null, 0, true)
-        return
+        await request({ timeout: this.config.heartbeatTimeout }, `http://localhost:${this.config.port}` + this.config.heartbeatPath, null, 0, true)
+        lastErr = null
+        break
       } catch (err) {
         lastErr = err
+        await new Promise((res) => {
+          setTimeout(res, this.config.heartbeatAttemptsWait)
+        })
+        // this.config.heartbeatAttemptsWait
       }
     }
 
-    return Promise.reject(new Error(`Version failed to start properly: ${lastErr.message}`))
+    if (lastErr) {
+      let err = new Error(`Version failed to start properly: ${lastErr.message}`)
+      err.stack = lastErr.stack
+      return Promise.reject(err)
+    }
+
+    if (this.config.cluster && !this.isSlave) {
+      this.__clusterWorkerDied = this.workerDied.bind(this)
+      this.cluster.on('exit', this.__clusterWorkerDied)
+    }
   }
 
   closeServer() {
+    if (this.config.cluster && !this.isSlave) {
+      if (this.__clusterWorkerDied) {
+        this.cluster.off('exit', this.__clusterWorkerDied)
+      }
+      this.__clusterWorkerDied = null
+
+      for (let i = 1; i <= this.config.cluster; i++) {
+        if (this.workers[i]) {
+          this.workers[i].process.kill()
+          this.workers[i] = null
+        }
+      }
+    }
     return this.http.closeServer()
   }
 }
diff --git a/core/client.mjs b/core/client.mjs
index 468a63f..7c1b602 100644
--- a/core/client.mjs
+++ b/core/client.mjs
@@ -2,6 +2,7 @@ import http from 'http'
 import https from 'https'
 import stream from 'stream/promises'
 import fs from 'fs'
+import Util from './util.mjs'
 
 function resolveRelative(from, to) {
   const resolvedUrl = new URL(to, new URL(from, 'resolve://'));
@@ -35,7 +36,7 @@ export function request(config, path, filePath = null, redirects, fastRaw = fals
 
   let req = null
 
-  return new Promise(function(resolve, reject) {
+  let orgErr = new Error(); return new Promise(function(resolve, reject) {
     if (!path) {
       return reject(new Error('Request path was empty'))
     }
@@ -52,7 +53,7 @@ export function request(config, path, filePath = null, redirects, fastRaw = fals
     let timer = setTimeout(function() {
       timedout = true
       if (req) { req.destroy() }
-      reject(new Error(`Request ${path} timed out after ${timeout}ms`))
+      reject(Util.combineStack(new Error(`Request ${path} timed out after ${timeout}ms`), orgErr))
     }, timeout)
 
     req = h.request({
@@ -81,7 +82,7 @@ export function request(config, path, filePath = null, redirects, fastRaw = fals
           })
         }, function(err) {
           if (err.code === 'ABORT_ERR') return
-          reject(err)
+          reject(Util.combineStack(err, orgErr))
         })
         // let file = fs.createWriteStream(filePath)
         // res.pipe(file)
@@ -113,11 +114,11 @@ export function request(config, path, filePath = null, redirects, fastRaw = fals
 
         if (err) {
           ac.abort()
-          if (!filePath) return reject(err)
+          if (!filePath) return reject(Util.combineStack(err, orgErr))
 
           // Do some cleanup in case we were in the middle of downloading file
           return fs.rm(filePath, function() {
-            reject(err)
+            reject(Util.combineStack(err))
           })
         }
         // Let the pipeline do the resolving so it can finish flusing before calling resolve
@@ -137,11 +138,11 @@ export function request(config, path, filePath = null, redirects, fastRaw = fals
       if (timedout) return
       let wrapped = new Error(`Error during request ${path}: ${err.message}`)
       wrapped.code = err.code
-      reject(wrapped)
+      reject(Util.combineStack(wrapped, orgErr))
     })
     req.on('timeout', function(err) {
       if (timedout) return
-      reject(err)
+      reject(Util.combineStack(err, orgErr))
     })
 
     req.end()
@@ -155,9 +156,9 @@ export function request(config, path, filePath = null, redirects, fastRaw = fals
           res.body = JSON.parse(res.body)
         } catch(e) {
           if (res.body.indexOf('<!DOCTYPE') < 100 || res.body.indexOf('<html') < 100) {
-            return Promise.reject(new Error('Error parsing body, expected JSON but got HTML instead: ' + res.body))
+            return Promise.reject(Util.combineStack(new Error('Error parsing body, expected JSON but got HTML instead: ' + res.body), orgErr))
           }
-          return Promise.reject(new Error(`Error parsing body ${res.body}: ${e.message}`))
+          return Promise.reject(Util.combineStack(new Error(`Error parsing body ${res.body}: ${e.message}`), orgErr))
         }
       }
     }
diff --git a/core/core.mjs b/core/core.mjs
index f6e399b..9c6aaa7 100644
--- a/core/core.mjs
+++ b/core/core.mjs
@@ -1,7 +1,9 @@
+import cluster from 'cluster'
+
+import { Low } from 'lowdb'
 import Application from './application.mjs'
 import Util from './util.mjs'
 import getLog from './log.mjs'
-import { Low } from 'lowdb'
 import StaticProvider from './providers/static.mjs'
 import GitProvider from './providers/git.mjs'
 
@@ -44,6 +46,7 @@ export default class Core {
     this.applications = []
     this.applicationMap = new Map()
     this._applicationFatalCrash = null
+    this.isSlave = cluster.isWorker
   }
 
   getApplication(name) {
@@ -59,15 +62,27 @@ export default class Core {
     this.log.info(`Found applications: ${names.join(', ')}.`)
 
     for (let name of names) {
+      if (this.isSlave && process.env.CLUSTER_APP_NAME !== name) {
+        continue
+      }
+
       try {
         let provConstructor = Core.providers.get(this.db.config[name].provider)
         let provider = new provConstructor(this.db.config[name])
-        await provider.checkConfig(this.db.config[name])
+
+        if (!this.isSlave) {
+          await provider.checkConfig(this.db.config[name])
+        }
+
+        let logName = name
+        if (this.isSlave && process.env.CLUSTER_APP_INDEX) {
+          logName += '-' + process.env.CLUSTER_APP_INDEX
+        }
 
         let application = new Application({
           db: this.db,
           util: this.util,
-          log: getLog(name, this.db.config[name].log || null),
+          log: getLog(logName, this.db.config[name].log || null),
           core: this,
         }, provider, name)
         this.applications.push(application)
@@ -86,14 +101,27 @@ export default class Core {
     if (this.running) return
     this.running = true
 
-    this.log.info(`Running updater on ${this.applications.length} apps`)
-    await Promise.all(this.applications.map((app) => {
-      return app.update().catch(err => {
-        app.ctx.log.error(err, `Error updating: ${err.message}`)
-      })
-    }))
+    if (!this.isSlave) {
+      this.log.info(`Running updater on ${this.applications.length} apps`)
+      await Promise.all(this.applications.map((app) => {
+        return app.update().catch(err => {
+          app.ctx.log.error(err, `Error updating: ${err.message}`)
+        })
+      }))
+    }
 
     let found = false
+    
+    if (this.isSlave) {
+      let app = this.getApplication(process.env.CLUSTER_APP_NAME)
+      try {
+        await app.runVersion(process.env.CLUSTER_APP_VERSION)
+      } catch (err) {
+        app.ctx.log.fatal(err)
+        return Promise.reject(err)
+      }
+      return
+    }
 
     for (let app of this.applications) {
       app.startAutoupdater()
@@ -136,6 +164,7 @@ export default class Core {
         application.ctx.log.warn(`Restarting for ${version.version} due to last run failing while not being in fresh state`)
         return this.restart(`Application ${name} has fresh false while attempting to run ${version.version} with stable -1`)
       }
+      
       await application.closeServer()
 
       this._applicationFatalCrash = this.criticalError.bind(this, application, version)
@@ -149,6 +178,7 @@ export default class Core {
         found = true
         version.stable = 1
         await this.db.write()
+        application.ctx.log.info(`${version.version} is up and running`)
         break
       } catch(err) {
         application.ctx.log.error(err, `Error starting ${version.version}: ${err.message}`)
diff --git a/core/db.mjs b/core/db.mjs
index cfa23e5..c1be18b 100644
--- a/core/db.mjs
+++ b/core/db.mjs
@@ -100,14 +100,15 @@ export default function GetDB(config, log, orgFilename = 'db.json') {
   db.write = function() {
     return this._write()
       // Do couple of retries. Sometimes it fails randomly doing atomic writes.
-      .catch(() => { return setTimeout(20) })
-      .then(() => { return this._write() })
-      .catch(() => { return setTimeout(50) })
-      .then(() => { return this._write() })
-      .catch(() => { return setTimeout(100) })
-      .then(() => { return this._write() })
+      .catch(() => { return setTimeout(20).then(() => { return this._write() }) })
+      .catch(() => { return setTimeout(50).then(() => { return this._write() }) })
+      .catch(() => { return setTimeout(100).then(() => { return this._write() }) })
       .catch((err) => {
-        this.log.error(err, 'Error saving to db')
+        try {
+          db.writeSync()
+        } catch {
+          this.log.error(err, 'Error saving to db')
+        }
       })
   }
 
diff --git a/core/log.mjs b/core/log.mjs
index 7c9eaa1..62dbb67 100644
--- a/core/log.mjs
+++ b/core/log.mjs
@@ -2,6 +2,22 @@
 import bunyan from 'bunyan-lite'
 import { setTimeout } from 'timers/promises'
 
+export function getDefaultStreams() {
+  if (process.env.NODE_ENV === 'production') {
+    return [{
+        path: 'log.log',
+        level: 'info',
+      }
+    ]
+  } else {
+    return [{
+        "stream": process.stdout,
+        "level": "debug"
+      }
+    ]
+  }
+}
+
 export default function getLog(name, streams = null, opts = {}) {
   let settings
   let ringbuffer = new bunyan.RingBuffer({ limit: 100 })
@@ -15,24 +31,9 @@ export default function getLog(name, streams = null, opts = {}) {
     })
   }
 
-  if (process.env.NODE_ENV === 'production') {
-    settings = {
-      "name": name,
-      "streams": streams || [{
-          path: 'log.log',
-          level: 'info',
-        }
-      ]
-    }
-  } else {
-    settings = {
-      "name": name,
-      "streams": streams || [{
-          "stream": process.stdout,
-          "level": "debug"
-        }
-      ]
-    }
+  settings = {
+    name: name,
+    streams: streams || getDefaultStreams()
   }
 
   let logger
@@ -122,6 +123,13 @@ export default function getLog(name, streams = null, opts = {}) {
       error: function() { return Promise.resolve() },
     }
   }
+  logger.on('error', function(err) {
+    if (process.env.NODE_ENV === 'production') {
+      logger.event.warn(`Error in logger ${name}: ${err.message}`)
+    } else {
+      console.log(`Error in logger ${name}: ${err.message}`)
+    }
+  })
   logger.ringbuffer = ringbuffer
   logger.ringbufferwarn = ringbufferwarn
 
diff --git a/core/runner.mjs b/core/runner.mjs
index 57268df..30f8dec 100644
--- a/core/runner.mjs
+++ b/core/runner.mjs
@@ -1,6 +1,7 @@
+import cluster from 'cluster'
 import Util from './util.mjs'
 import fs from 'fs/promises'
-import getLog from './log.mjs'
+import getLog, { getDefaultStreams } from './log.mjs'
 import GetDB from './db.mjs'
 import Core from './core.mjs'
 
@@ -21,8 +22,14 @@ export async function runner(root_import_meta_url, configname = 'config.json', d
       throw new Error(`critical error opening ${fullpath}: ${err.message}`)
     }
   }
+
+  let streams = getDefaultStreams()
+
+  if (cluster.isWorker) {
+    streams[0].level = 'error'
+  }
   
-  const log = getLog(config.name)
+  const log = getLog(config.name, streams)
   runner.log = log
   const db = await GetDB(config, log, util.getPathFromRoot('./' + dbname))
   
diff --git a/core/util.mjs b/core/util.mjs
index d9aedf3..417560f 100644
--- a/core/util.mjs
+++ b/core/util.mjs
@@ -5,6 +5,11 @@ import { spawn, execSync } from 'child_process'
 import { fileURLToPath, pathToFileURL } from 'url'
 
 export default class Util {
+  static combineStack(err, appendErr) {
+    err.stack = err.stack + '\nFrom:\n' + appendErr.stack.split('\n').slice(1).join('\n') + '\n'
+    return err
+  }
+
   constructor(root_import_meta_url) {
     this._root_import_meta_url = root_import_meta_url
   }
@@ -79,6 +84,10 @@ export default class Util {
         if (!valid)
           continue
       }
+      if (config[key].cluster != null && (typeof(config[key].cluster) !== 'number' || config[key].cluster > 100 || config[key].cluster < 0))
+        continue
+      if (config[key].clusterWaitOnCrash != null && (typeof(config[key].clusterWaitOnCrash) !== 'number' || config[key].clusterWaitOnCrash < 10))
+        continue
 
       out.push(key)
     }
@@ -93,6 +102,13 @@ export default class Util {
     return util.getPathFromRoot('../bin/7zdec')
   }
 
+  getNpmExecutable() {
+    if (process.platform === 'win32') {
+      return 'npm.cmd'
+    }
+    return 'npm'
+  }
+
   verifyConfig(config) {
     if (!config.name) throw new Error('name is missing in config.json')
     if (this.getAppNames(config).length === 0) throw new Error('no application was found in config')
diff --git a/package.json b/package.json
index 87d66a4..5b70819 100644
--- a/package.json
+++ b/package.json
@@ -5,7 +5,7 @@
   "main": "index.mjs",
   "scripts": {
     "dev": "nodemon --watch dev/api --watch core --watch runner.mjs --watch db.mjs --watch log.mjs runner.mjs | bunyan",
-    "test": "eltro \"test/**/*.test.mjs\" -r dot",
+    "test": "eltro -t 250 \"test/**/*.test.mjs\" -r dot",
     "test:integration": "eltro \"test/**/*.test.integration.mjs\" -r list",
     "test:test": "eltro \"test/application.test.integration.mjs\" -r list",
     "test:spec": "eltro \"test/**/*.test.mjs\" -r list",
@@ -52,6 +52,6 @@
     "lowdb": "^3.0.0"
   },
   "devDependencies": {
-    "eltro": "^1.3.0"
+    "eltro": "^1.3.1"
   }
 }
diff --git a/test/application.cluster.test.mjs b/test/application.cluster.test.mjs
new file mode 100644
index 0000000..33be88f
--- /dev/null
+++ b/test/application.cluster.test.mjs
@@ -0,0 +1,122 @@
+import { Eltro as t, assert, stub } from 'eltro'
+import fs from 'fs/promises'
+import Application from '../core/application.mjs'
+import Util from '../core/util.mjs'
+import lowdb from '../core/db.mjs'
+import StaticProvider from '../core/providers/static.mjs'
+import { createFakeContext } from './helpers.mjs'
+import HttpServer from '../core/http.mjs'
+
+const util = new Util(import.meta.url)
+
+
+t.describe('#runVersion("version") cluster mode', function() {
+  const assertPort = 22345
+  const assertClusterSize = Math.floor(Math.random() * (8 - 2 + 1) + 2)
+  const http = new HttpServer()
+  let handler
+  let cluster
+  let workers
+  let ctx
+  let app
+
+  t.beforeEach(function() {
+    return createFakeContext({ testnoexisting: { cluster: assertClusterSize } }, util, null)
+      .then(function(res) {
+        workers = []
+        ctx = res
+        let provider = new StaticProvider()
+        cluster = {
+          on: stub(),
+          off: stub(),
+          fork: stub().returnWith(function() {
+            let worker = {
+              on: stub(),
+              once: stub(),
+              process: {
+                kill: stub(),
+              }
+            }
+            workers.push(worker)
+            return worker
+          }),
+          isWorker: false,
+        }
+        app = new Application(ctx, provider, 'testnoexisting', { cluster })
+        app.config.port = assertPort
+        app.workerDied = stub()
+        return app.ctx.db.write()
+      })
+  })
+
+  t.afterEach(function() {
+    return Promise.all([
+      app.closeServer(),
+    ])
+  })
+
+  t.before(function() {
+    handler = function(req, res) {
+      res.writeHead(200)
+      res.end('{}')
+    }
+    let server = http.createServer(function(req, res) {
+      req.on('error', function() { })
+      res.on('error', function() { })
+      res.on('finish', function() { })
+      handler(req, res)
+    })
+
+    return server.listenAsync(assertPort)
+  })
+
+  t.after(function() {
+    return http.closeServer()
+  })
+
+  t.test('should call fork for entire cluster and attach handlers correctly', async function() {
+    let lastErr = null
+    for (let i = 1; i <= assertClusterSize; i++) {
+      assert.strictEqual(app.workers[i], null)
+    }
+    handler = function(req, res) {
+      try {
+        assert.notOk(cluster.on.called)
+        assert.notOk(app.__clusterWorkerDied)
+        lastErr = false
+      } catch (err) {
+        lastErr = err
+      }
+      res.writeHead(200)
+      res.end('{}')
+    }
+    const assertVersion = 'v11.22.33'
+
+    await app.runVersion(assertVersion)
+
+    assert.strictEqual(cluster.fork.callCount, assertClusterSize)
+
+    for (let i = 1; i <= assertClusterSize; i++) {
+      assert.ok(app.workers[i])
+      assert.strictEqual(app.workers[i], workers[i - 1])
+      assert.strictEqual(cluster.fork.getCallN(i)[0].CLUSTER_APP_NAME, app.name)
+      assert.strictEqual(cluster.fork.getCallN(i)[0].CLUSTER_APP_VERSION, assertVersion)
+      assert.strictEqual(app.workers[i].w_id, i)
+      assert.strictEqual(app.workers[i].listening, false)
+      assert.ok(app.workers[i].started)
+      assert.ok(new Date() - app.workers[i].started < 100 && new Date() - app.workers[i].started >= 0)
+    }
+
+    assert.strictEqual(lastErr, false)
+    assert.strictEqual(cluster.on.callCount, 1)
+    assert.ok(app.__clusterWorkerDied)
+    assert.strictEqual(cluster.on.firstCall[0], 'exit')
+    assert.strictEqual(cluster.on.firstCall[1], app.__clusterWorkerDied)
+    assert.notStrictEqual(app.workerDied, app.__clusterWorkerDied)
+    assert.notOk(app.workerDied.called)
+
+    app.__clusterWorkerDied()
+
+    assert.ok(app.workerDied.called)
+  })
+})
diff --git a/test/application.run.test.mjs b/test/application.run.test.mjs
index e4b059f..fbda27a 100644
--- a/test/application.run.test.mjs
+++ b/test/application.run.test.mjs
@@ -15,7 +15,7 @@ t.describe('#runVersion("static")', function() {
 
   const defaultHandler = function(orgHandler) {
     let handler = orgHandler || function (req, res) {
-      res.writeHead(204); res.end(JSON.stringify({ a: 1 }))
+      res.writeHead(200); res.end(JSON.stringify({ a: 1 }))
     }
     return function(http, port, ctx) {
       const server = http.createServer(handler)
@@ -36,7 +36,7 @@ t.describe('#runVersion("static")', function() {
   })
 
   t.afterEach(function() {
-    return app.http.closeServer()
+    return app.closeServer()
   })
 
   t.test('should throw if http is not called', async function() {
@@ -98,6 +98,7 @@ t.describe('#runVersion("static")', function() {
       res.end(JSON.stringify({ a: 1 }))
     }
     app.config.heartbeatAttempts = 3
+    app.config.heartbeatAttemptsWait = 5
     app.registerModule(defaultHandler(handler))
 
     assert.strictEqual(app.fresh, true)
@@ -116,7 +117,8 @@ t.describe('#runVersion("static")', function() {
       called++
     }
     app.config.heartbeatAttempts = 2
-    app.config.heartbeatAttemptsWait = 30
+    app.config.heartbeatTimeout = 30
+    app.config.heartbeatAttemptsWait = 10
     app.registerModule(defaultHandler(handler))
 
     assert.strictEqual(app.fresh, true)
@@ -129,7 +131,7 @@ t.describe('#runVersion("static")', function() {
     assert.match(err.message, /time/i)
     assert.match(err.message, /out/i)
     assert.match(err.message, /30ms/i)
-    assert.ok(end - start > app.config.heartbeatAttempts * app.config.heartbeatAttemptsWait)
+    assert.ok(end - start > app.config.heartbeatAttempts * (app.config.heartbeatTimeout + app.config.heartbeatAttemptsWait))
     assert.strictEqual(called, 2)
     assert.strictEqual(ctx.db.data.core.testapp.active, 'static')
   })
@@ -145,13 +147,14 @@ t.describe('#runVersion("static")', function() {
       }
     }
     app.config.heartbeatAttempts = 3
+    app.config.heartbeatAttemptsWait = 5
     app.registerModule(defaultHandler(handler))
 
     let err = await assert.isRejected(app.runVersion('static'))
     assert.match(err.message, /failed/i)
     assert.match(err.message, /400/i)
 
-    await app.http.closeServer()
+    await app.closeServer()
     app.registerModule(defaultHandler(handler))
 
     app.config.heartbeatPath = assertPath
@@ -159,6 +162,24 @@ t.describe('#runVersion("static")', function() {
 
     assert.strictEqual(ctx.db.data.core.testapp.active, 'static')
   })
+  
+  t.test('should not check heartbeat if slave', async function() {
+    let called = 0
+    const handler = function(req, res) {
+      called++
+      res.statusCode = 400
+      res.end(JSON.stringify({ a: 1 }))
+    }
+    app.registerModule(defaultHandler(handler))
+    app.isSlave = true
+
+    assert.strictEqual(app.fresh, true)
+    await app.runVersion('static')
+    assert.strictEqual(app.fresh, false)
+
+    assert.strictEqual(called, 0)
+    assert.strictEqual(ctx.db.data.core.testapp.active, 'static')
+  })
 })
 
 t.describe('#runVersion("version")', function() {
@@ -190,7 +211,7 @@ t.describe('#runVersion("version")', function() {
   t.afterEach(function() {
     return Promise.all([
       fs.rm(assertConfig),
-      app.http.closeServer(),
+      app.closeServer(),
     ])
   })
 
diff --git a/test/application.test.integration.mjs b/test/application.test.integration.mjs
index 4cf1e59..da28303 100644
--- a/test/application.test.integration.mjs
+++ b/test/application.test.integration.mjs
@@ -32,7 +32,7 @@ t.after(function() {
     })
 })
 
-t.timeout(10000).test('should run update and install correctly', async function(){
+t.skip().timeout(10000).test('should run update and install correctly', async function(){
   try {
     await app.update()
   } catch (err) {
diff --git a/test/application.test.mjs b/test/application.test.mjs
index b52cb78..cb2ebac 100644
--- a/test/application.test.mjs
+++ b/test/application.test.mjs
@@ -58,19 +58,84 @@ t.describe('constructor()', function() {
     assert.strictEqual(app.config.heartbeatAttempts, 5)
     assert.strictEqual(app.config.heartbeatAttemptsWait, 2 * 1000)
     assert.strictEqual(app.config.heartbeatPath, '/')
+    assert.strictEqual(app.config.clusterWaitOnCrash, 1 * 1000)
     assert.strictEqual(app.ctx.db, ctx.db)
     assert.strictEqual(app.ctx.app, app)
     assert.strictEqual(app.ctx.util, ctx.util)
     assert.strictEqual(app.name, assertName)
     assert.strictEqual(app.fresh, true)
     assert.strictEqual(app.running, false)
+    assert.strictEqual(app.monitoringCluster, false)
+    assert.deepStrictEqual(app.workers, {})
+    assert.strictEqual(app.isSlave, false)
     assert.ok(app.http)
     assert.ok(app.http.sockets)
     assert.strictEqual(typeof(app.http.createServer), 'function')
     assert.strictEqual(typeof(app.http.closeServer), 'function')
   })
 
-  
+  t.test('should support overriding defaults', function() {
+    const assertTest = {
+      a: 1,
+      updateEvery: 10,
+      startWaitUntilFail: 10,
+      heartbeatTimeout: 10,
+      heartbeatAttempts: 10,
+      heartbeatAttemptsWait: 10,
+      heartbeatPath: '/asdf',
+      clusterWaitOnCrash: 10,
+    }
+    const assertName = 'test'
+    ctx.db.config = {
+      test: assertTest,
+      app: { b: 2},
+      manage: { c: 3 },
+    }
+
+    let app = new Application(ctx, {}, assertName)
+    assert.notStrictEqual(app.config, assertTest)
+    assert.strictEqual(app.config.a, assertTest.a)
+    assert.strictEqual(app.config.updateEvery, 10)
+    assert.strictEqual(app.config.startWaitUntilFail, 10)
+    assert.strictEqual(app.config.heartbeatTimeout, 10)
+    assert.strictEqual(app.config.heartbeatAttempts, 10)
+    assert.strictEqual(app.config.heartbeatAttemptsWait, 10)
+    assert.strictEqual(app.config.heartbeatPath, '/asdf')
+    assert.strictEqual(app.config.clusterWaitOnCrash, 10)
+  })
+
+  t.test('should fill out workers indexes if is master', function() {
+    const assertTest = { a: 1, cluster: 2 }
+    const assertName = 'test'
+    ctx.db.config = {
+      test: assertTest,
+      app: { b: 2},
+      manage: { c: 3 },
+    }
+
+    let app = new Application(ctx, {}, assertName)
+    assert.notStrictEqual(app.config, assertTest)
+    assert.strictEqual(app.config.a, assertTest.a)
+    assert.deepStrictEqual(app.workers, {
+      1: null,
+      2: null,
+    })
+  })
+
+  t.test('should leave workers empty if not master', function() {
+    const assertTest = { a: 1, cluster: 2 }
+    const assertName = 'test'
+    ctx.db.config = {
+      test: assertTest,
+      app: { b: 2},
+      manage: { c: 3 },
+    }
+
+    let app = new Application(ctx, {}, assertName, { cluster: { isWorker: true } })
+    assert.notStrictEqual(app.config, assertTest)
+    assert.strictEqual(app.config.a, assertTest.a)
+    assert.deepStrictEqual(app.workers, {})
+  })
 
   t.test('should not default updateEvery if its zero', function() {
     const assertTest = { a: 1, updateEvery: 0 }
@@ -107,7 +172,7 @@ t.describe('constructor()', function() {
   })
 })
 
-t.timeout(250).describe('#startAutoupdater()', function() {
+t.describe('#startAutoupdater()', function() {
   let ctx
 
   t.beforeEach(function() {
@@ -124,6 +189,20 @@ t.timeout(250).describe('#startAutoupdater()', function() {
     app.startAutoupdater()
   })
   
+  t.test('should do nothing if isSlave but should warn', async function() {
+    const stubInterval = stub()
+    stubInterval.throws(new Error('should not be seen'))
+    let app = new Application(ctx, { }, 'teststatic', { setInterval: stubInterval })
+    app.ctx.log.warn.reset()
+    assert.notOk(app.ctx.log.warn.called)
+    app.isSlave = true
+
+    app.startAutoupdater()
+
+    assert.ok(app.ctx.log.warn.called)
+    assert.match(app.ctx.log.warn.firstCall[0], /slave/i)
+  })
+  
   t.test('should do nothing if updateEvery is zero', async function() {
     const stubInterval = stub()
     stubInterval.throws(new Error('should not be seen'))
@@ -222,15 +301,19 @@ t.timeout(250).describe('#startAutoupdater()', function() {
   })
 })
 
-t.timeout(250).describe('#closeServer()', function() {
+t.describe('#closeServer()', function() {
   let app
+  let cluster
   let stubCloseServer
 
   t.beforeEach(function() {
+    cluster = {
+      off: stub(),
+    }
     return createFakeContext()
       .then(function(res) {
         let provider = createProvider()
-        app = new Application(res, provider, 'testapp')
+        app = new Application(res, provider, 'testapp', { cluster: cluster })
         app.http.closeServer = stubCloseServer = stub().resolves()
       })
   })
@@ -244,12 +327,109 @@ t.timeout(250).describe('#closeServer()', function() {
     assert.strictEqual(err, assertError)
   })
 
+  t.test('should kill entire cluster if cluster master', async function() {
+    let workers = {}
+    let handle = app.__clusterWorkerDied = function() {}
+    app.config.cluster = Math.floor(Math.random() * (10 - 4 + 1) + 4)
+    for (let i = 1; i <= app.config.cluster; i++) {
+      if (i % 2 === 0) {
+        workers[i] = app.workers[i] = {
+          process: {
+            kill: stub().returnWith(function() {
+              assert.strictEqual(app.__clusterWorkerDied, null)
+              assert.strictEqual(cluster.off.callCount, 1)
+              assert.strictEqual(cluster.off.firstCall[0], 'exit')
+              assert.strictEqual(cluster.off.firstCall[1], handle)
+            })
+          }
+        }
+      } else {
+        workers[i] = app.workers[i] = null
+      }
+    }
+
+    await app.closeServer()
+
+    for (let i = 1; i <= app.config.cluster; i++) {
+      if (workers[i]) {
+        assert.ok(workers[i].process.kill.called)
+        assert.strictEqual(app.__clusterWorkerDied, null)
+      }
+    }
+  })
+
   t.test('otherwise should work fine', async function() {
     await app.closeServer()
   })
 })
 
-t.timeout(250).describe('#update()', function() {
+t.describe('#workerDied()', function() {
+  let app
+  let stubTimeout
+  let stubFork
+  
+  t.beforeEach(function() {
+    stubTimeout = stub()
+    return createFakeContext()
+      .then(function(res) {
+        let provider = createProvider()
+        app = new Application(res, provider, 'testapp', { setTimeout: stubTimeout })
+        app.startForkProcess = stubFork = stub()
+      })
+  })
+
+  t.test('should do nothing if worker is not found at index', function() {
+    const assertWorkerId = 2
+    const assertWorker = { a: 1, w_id: assertWorkerId }
+    stubTimeout.throws(new Error('should not be seen'))
+    stubFork.throws(new Error('should not be seen'))
+    app.workers[1] = assertWorker
+
+    app.workerDied(assertWorker)
+  })
+
+  t.test('should mark worker as null and call setTimeout', function() {
+    const assertWorkerId = 2
+    const assertTimeoutDuration = 12421
+    const assertVersion = 'v11.22.33'
+    const assertWorker = { a: 1, w_id: assertWorkerId }
+    app.ctx.db.data.core[app.name].active = assertVersion
+    app.workers[assertWorkerId] = assertWorker
+    app.clusterWaitOnCrash = assertTimeoutDuration
+
+    app.workerDied(assertWorker)
+
+    assert.strictEqual(app.workers[assertWorkerId], null)
+    assert.ok(stubTimeout.called)
+    assert.strictEqual(typeof(stubTimeout.firstCall[0]), 'function')
+    assert.strictEqual(stubTimeout.firstCall[1], assertTimeoutDuration)
+    assert.notOk(stubFork.called)
+
+    stubTimeout.firstCall[0]()
+
+    assert.ok(stubFork.called)
+    assert.ok(stubFork.firstCall[0], assertWorkerId)
+    assert.ok(stubFork.firstCall[1], assertVersion)
+  })
+
+  t.test('setTimeout should not call startForkProcess if one was already started', function() {
+    const assertWorkerId = 2
+    const assertWorker = { a: 1, w_id: assertWorkerId }
+    app.workers[assertWorkerId] = assertWorker
+
+    app.workerDied(assertWorker)
+
+    assert.strictEqual(app.workers[assertWorkerId], null)
+
+    app.workers[assertWorkerId] = { a : 2 }
+
+    stubTimeout.firstCall[0]()
+
+    assert.notOk(stubFork.called)
+  })
+})
+
+t.describe('#update()', function() {
   let ctx
   let app
   let provider
@@ -321,6 +501,23 @@ t.timeout(250).describe('#update()', function() {
     assert.strictEqual(stubWrite.callCount, 2)
   })
 
+  t.test('should do nothing if slave but warn', async function() {
+    stubWrite.reset().resolves()
+
+    app.isSlave = true
+    app.ctx.log.warn.reset()
+    assert.notOk(app.ctx.log.warn.called)
+
+    let result = await app.update()
+
+    assert.strictEqual(result, null)
+    assert.notOk(ctx.db.data.core.teststatic)
+    assert.notOk(stubWrite.called)
+
+    assert.ok(app.ctx.log.warn.called)
+    assert.match(app.ctx.log.warn.firstCall[0], /slave/i)
+  })
+
   t.test('multiple calls should be safe', async function() {
     ctx.db.data.core.testapp.updater = ''
 
@@ -638,7 +835,7 @@ t.timeout(250).describe('#update()', function() {
     assert.notOk(stubUpdated.called)
     assert.strictEqual(app.updating, false)
     assert.strictEqual(err, assertError)
-    assert.strictEqual(stubRunCommand.firstCall[0], 'npm.cmd')
+    assert.strictEqual(stubRunCommand.firstCall[0], util.getNpmExecutable())
     assert.ok(stubRunCommand.firstCall[1])
     assert.strictEqual(stubRunCommand.firstCall[1][0], 'install')
     assert.ok(stubRunCommand.firstCall[1].includes('--production'), 'should have --production')
@@ -845,7 +1042,7 @@ t.timeout(250).describe('#update()', function() {
   })
 })
 
-t.timeout(250).describe('#registerModule()', function() {
+t.describe('#registerModule()', function() {
   const assertAppName = 'testappregister'
   let ctx
   let app
diff --git a/test/core.cluster.test.mjs b/test/core.cluster.test.mjs
new file mode 100644
index 0000000..7823c02
--- /dev/null
+++ b/test/core.cluster.test.mjs
@@ -0,0 +1,236 @@
+import { Eltro as t, assert, stub } from 'eltro'
+import fs from 'fs/promises'
+import Core from '../core/core.mjs'
+import Util from '../core/util.mjs'
+import { createFakeLog } from './helpers.mjs'
+import StaticProvider from '../core/providers/static.mjs'
+import lowdb from '../core/db.mjs'
+
+const util = new Util(import.meta.url)
+const log = createFakeLog()
+let db
+
+t.before(function() {
+  return lowdb({}, log, null).then(function(res) {
+    db = res
+  })
+})
+
+t.describe('#init()', function() {
+  const assertProviderName = 'Kyousuu Gakku Gogyou Kikan'
+  let core
+  let fakeUtil
+  let fakeProvider
+  let fakeProviderConfig
+
+  function FakeProvider(config) {
+    fakeProvider(config)
+    this.static = true
+    this.checkConfig = fakeProviderConfig
+  }
+
+  t.beforeEach(function() {
+    log.error.reset()
+    core = new Core(db, util, log)
+    core.util = fakeUtil = {
+      verifyConfig: stub(),
+      getAppNames: stub().returns([]),
+    }
+    fakeProvider = stub()
+    fakeProviderConfig = stub()
+    Core.providers.set(assertProviderName, FakeProvider)
+    core.isSlave = true
+  })
+
+  t.after(function() {
+    return Promise.all([
+      fs.rm('./log_test_1.log', { recursive: true, force: true }).catch(function() {}),
+    ])
+  })
+
+  t.test('should not call provider checkConfig if isSlave', async function() {
+    const assertAppName = 'Zetsubou'
+    const assertConfig = {
+      [assertAppName]: {
+        provider: assertProviderName,
+      }
+    }
+    db.config = assertConfig
+    process.env.CLUSTER_APP_NAME = assertAppName
+
+    const assertError = new Error('Shousou')
+    fakeProviderConfig.rejects(assertError)
+    fakeUtil.getAppNames.returns([assertAppName])
+    
+    await core.init()
+    assert.notOk(fakeProviderConfig.called)
+  })
+
+  t.test('should only create an application with the environment app name', async function() {
+    const assertAppName = 'Yasashii Ketsumatsu'
+    const assertAppSecondaryName = 'Big Time'
+    const assertTestString = 'Serozore no Omoi'
+    const assertConfig = {
+      [assertAppName]: {
+        provider: assertProviderName,
+        teststring: assertTestString,
+      },
+      [assertAppSecondaryName]: {
+        provider: assertProviderName,
+        teststring: assertTestString,
+      },
+    }
+    db.config = assertConfig
+    process.env.CLUSTER_APP_NAME = assertAppName
+
+    fakeUtil.getAppNames.returns([assertAppSecondaryName, assertAppName])
+    assert.strictEqual(core.applications.length, 0)
+
+    await core.init()
+
+    assert.strictEqual(core.applications.length, 1)
+    assert.ok(core.getApplication(assertAppName))
+    assert.notOk(core.getApplication(assertAppSecondaryName))
+    
+    let application = core.getApplication(assertAppName)
+    assert.strictEqual(core.applications[0], application)
+    assert.strictEqual(application.name, assertAppName)
+    assert.strictEqual(application.ctx.db, core.db)
+    assert.strictEqual(application.ctx.util, core.util)
+    assert.notStrictEqual(application.ctx.log, core.log)
+    assert.strictEqual(application.ctx.core, core)
+    assert.strictEqual(application.config.teststring, assertTestString)
+    assert.ok(application.fresh)
+    assert.ok(application.provider instanceof FakeProvider)
+  })
+})
+
+t.describe('#run()', function() {
+  let core
+  let testAppOneName
+  let testAppTwoName
+  let stubRunApplication
+
+  t.beforeEach(function() {
+    testAppOneName = 'Tenshi'
+    testAppTwoName = 'no CLOVER'
+    db.data.core = {
+      [testAppOneName]: {
+        versions: []
+      },
+      [testAppTwoName]: {
+        versions: []
+      },
+    }
+    core = new Core(db, util, log)
+    core.runApplication = stubRunApplication = stub().resolves()
+    core.isSlave = true
+    db.write = stub().resolves()
+    log.info.reset()
+    log.warn.reset()
+    log.error.reset()
+    for (let name of [testAppOneName, testAppTwoName]) {
+      let onOrOnce = stub()
+      let app = {
+        name: name,
+        fresh: false,
+        on: onOrOnce,
+        once: onOrOnce,
+        ctx: {
+          log: {
+            info: stub(),
+            warn: stub(),
+            error: stub(),
+            fatal: stub(),
+          },
+        },
+        runVersion: stub().resolves(),
+        update: stub().resolves(),
+        startAutoupdater: stub(),
+      }
+      core.applicationMap.set(name, app)
+      core.applications.push(app)
+    }
+    process.env.CLUSTER_APP_NAME = testAppTwoName
+  })
+
+  t.test('should not call update', async function() {
+    const assertFirstError = new Error('Manatsu')
+    const assertSecondError = new Error('no Photograph')
+    core.applicationMap.get(testAppOneName).update.rejects(assertFirstError)
+    core.applicationMap.get(testAppTwoName).update.rejects(assertSecondError)
+
+    await core.run()
+    
+    assert.notOk(core.applications[0].update.called)
+    assert.notOk(core.applications[1].update.called)
+  })
+  
+
+  t.test('app.on updated should not be hooked', async function() {
+    assert.notOk(core.applicationMap.get(testAppOneName).once.called)
+    assert.notOk(core.applicationMap.get(testAppTwoName).once.called)
+    assert.notOk(core.applicationMap.get(testAppOneName).on.called)
+    assert.notOk(core.applicationMap.get(testAppTwoName).on.called)
+
+    core.runApplication.returnWith(function(app) {
+      assert.notOk(app.once.called)
+      assert.notOk(app.on.called)
+      return Promise.resolve()
+    })
+
+    await core.run()
+
+    assert.notOk(core.applicationMap.get(testAppOneName).once.called)
+    assert.notOk(core.applicationMap.get(testAppTwoName).once.called)
+    assert.notOk(core.applicationMap.get(testAppOneName).on.called)
+    assert.notOk(core.applicationMap.get(testAppTwoName).on.called)
+  })
+
+  t.test('should not call startAutoupdater', async function() {
+    stubRunApplication.rejects(new Error('not seen'))
+    assert.notOk(core.applications[0].startAutoupdater.called)
+    assert.notOk(core.applications[1].startAutoupdater.called)
+
+    await core.run()
+    
+    assert.notOk(core.applications[0].startAutoupdater.called)
+    assert.notOk(core.applications[1].startAutoupdater.called)
+  })
+
+  t.test('should be safe to call multiple times', async function() {
+    await core.run()
+
+    assert.strictEqual(core.applicationMap.get(testAppOneName).runVersion.callCount, 0)
+    assert.strictEqual(core.applicationMap.get(testAppTwoName).runVersion.callCount, 1)
+
+    await core.run()
+    await core.run()
+    await core.run()
+    await core.run()
+
+    assert.strictEqual(core.applicationMap.get(testAppOneName).runVersion.callCount, 0)
+    assert.strictEqual(core.applicationMap.get(testAppTwoName).runVersion.callCount, 1)
+  })
+
+  t.test('should call runVersion on selected application', async function() {
+    const assertFirstError = new Error('Manatsu')
+    const assertSecondError = new Error('no Photograph')
+    const assertVersion = 'v11.22.33'
+    core.applicationMap.get(testAppOneName).runVersion.rejects(assertFirstError)
+    core.applicationMap.get(testAppTwoName).runVersion.rejects(assertSecondError)
+    
+    process.env.CLUSTER_APP_NAME = testAppTwoName
+    process.env.CLUSTER_APP_VERSION = assertVersion
+
+    let err = await assert.isRejected(core.run())
+    
+    let app = core.applicationMap.get(testAppTwoName)
+    assert.strictEqual(core.applicationMap.get(testAppOneName).runVersion.callCount, 0)
+    assert.strictEqual(app.runVersion.callCount, 1)
+    assert.strictEqual(app.runVersion.firstCall[0], assertVersion)
+    assert.strictEqual(app.ctx.log.fatal.callCount, 1)
+    assert.strictEqual(app.ctx.log.fatal.firstCall[0], assertSecondError)
+    assert.strictEqual(err, assertSecondError)
+  })
+})
diff --git a/test/core.test.integration.mjs b/test/core.test.integration.mjs
index c34a8c7..302baff 100644
--- a/test/core.test.integration.mjs
+++ b/test/core.test.integration.mjs
@@ -1,6 +1,6 @@
 import { Eltro as t, assert} from 'eltro'
 import fs from 'fs/promises'
-import http from 'http'
+import HttpServer from '../core/http.mjs'
 import Util from '../core/util.mjs'
 import { request } from '../core/client.mjs'
 import { setTimeout } from 'timers/promises'
@@ -10,438 +10,520 @@ import getLog from '../core/log.mjs'
 
 const util = new Util(import.meta.url)
 const port = 61412
+const turnDebuggingOn = false
 
-t.timeout(10000).describe('', function() {
-  let server = null
-  let prefix = `http://localhost:${port}/`
-  let files = []
-  let logs = []
-  let versions = []
-  let processor
-  let integrationLog = getLog('test.integration', [])
-  let compressorPath = util.getPathFromRoot('./7za.exe')
-  if (process.platform !== 'win32') {
-    compressorPath = util.getPathFromRoot('./7zas')
-  }
+const runners = [
+  ['runner.mjs', 'testapp'],
+  ['runner_cluster.mjs', 'testappcluster'],
+]
 
-  t.before(function(cb) {
-    server = http.createServer(function(req, res) {
-      req.on('error', function(err) {
-        integrationLog.error(err, 'error')
-      })
-      res.on('error', function(err) {
-        integrationLog.error(err, 'error')
-      })
-
-      integrationLog.info('[SERVER] got request ' + req.url)
-
-      if (req.url === '/releases') {
-        res.statusCode = 200
-        let output = versions.map(x => {
-          return {
-            name: x[0],
-            body: x[1],
-            assets: [{
-              name: x[2],
-              browser_download_url: prefix + 'files/' + x[2]
-            }]
-          }
+runners.forEach(function([runnerName, appname]) {
+  t.timeout(10000).describe(runnerName, function() {
+    let wasSuccessful = false
+    let http = null
+    let server = null
+    let prefix = `http://localhost:${port}/`
+    let files = [util.getPathFromRoot('./testappcluster')]
+    let logs = []
+    let allLogs = []
+    let versions = []
+    let processor
+    let integrationLog = getLog('test.integration', [])
+    let compressorPath = util.getPathFromRoot('./7za.exe')
+    if (process.platform !== 'win32') {
+      compressorPath = util.getPathFromRoot('./7zas')
+    }
+  
+    t.before(function() {
+      http = new HttpServer()
+  
+      server = http.createServer(function(req, res) {
+        req.on('error', function(err) {
+          integrationLog.error(err, 'error')
         })
-        res.end(JSON.stringify(output));
-        return
-      } else if (req.url.startsWith('/files')) {
-        let filename =  req.url.substring(req.url.lastIndexOf('/') + 1)
-        return fs.open(util.getPathFromRoot('./' + filename))
-        .then(function(file) {
-          pipeline(file.createReadStream(), res, function(err) {
-            if (err) {
-              console.log(err)        
-              res.statusCode = 404
-              res.end(JSON.stringify({ error: 'unknown url' }))
+        res.on('error', function(err) {
+          integrationLog.error(err, 'error')
+        })
+  
+        integrationLog.info('[SERVER] got request ' + req.url)
+  
+        if (req.url === '/releases') {
+          res.statusCode = 200
+          let output = versions.map(x => {
+            return {
+              name: x[0],
+              body: x[1],
+              assets: [{
+                name: x[2],
+                browser_download_url: prefix + 'files/' + x[2]
+              }]
             }
           })
-        }).catch(function(err) {
-          console.log(err)        
-          res.statusCode = 404
-          res.end(JSON.stringify({ error: 'unknown url' }))
-        })
+          res.end(JSON.stringify(output));
+          return
+        } else if (req.url.startsWith('/files')) {
+          let filename =  req.url.substring(req.url.lastIndexOf('/') + 1)
+          return fs.open(util.getPathFromRoot('./' + filename))
+          .then(function(file) {
+            pipeline(file.createReadStream(), res, function(err) {
+              if (err) {
+                console.log(err)        
+                res.statusCode = 404
+                res.end(JSON.stringify({ error: 'unknown url' }))
+              }
+            })
+          }).catch(function(err) {
+            console.log(err)        
+            res.statusCode = 404
+            res.end(JSON.stringify({ error: 'unknown url' }))
+          })
+        }
+        
+        res.statusCode = 404
+        res.end(JSON.stringify({ error: 'unknown url' }))
+      })
+  
+      return fs.rm(util.getPathFromRoot('./db.json'), { force: true })
+      .then(function() {
+        return server.listenAsync(port)
+      })
+    })
+  
+    t.after(function() {
+      if (!turnDebuggingOn && !wasSuccessful) {
+        for (let i = 0; i < allLogs.length; i++) {
+          prettyPrintMessage(allLogs[i])
+        }
       }
+
+      return Promise.all(files.map(function(file) {
+        return fs.rm(file, { force: true, recursive: true })
+      }))
+      .then(function() {
+        if (processor && !processor.exitCode) {
+          processor.kill()
       
-      res.statusCode = 404
-      res.end(JSON.stringify({ error: 'unknown url' }))
-    })
-
-    fs.rm(util.getPathFromRoot('./db.json'), { force: true }).then(function() {
-      server.listen(port, cb)
-    }, cb)
-  })
-
-  t.after(function() {
-    return Promise.all(files.map(function(file) {
-      return fs.rm(file, { force: true, recursive: true })
-    }))
-    .then(function() {
-      if (processor && !processor.exitCode) {
-        processor.kill()
-      }
-    })
-  })
-
-  const version_1_stable = `
-  export function start(http, port, ctx) {
-    const server = http.createServer(function (req, res) {
-      res.writeHead(200);
-      res.end(JSON.stringify({ version: 'v1' }))
-    })
-
-    return server.listenAsync(port, '0.0.0.0')
-      .then(() => {
-        ctx.log.info({ port: port, listening: true }, \`Server is listening on \${port} serving v1\`)
+          return waitUntilClosed()
+        }
+      }).then(function() {
+        return http.closeServer()
       })
-  }
-  `
-
-  const version_2_nolisten = `
-  export function start(http, port, ctx) {
-  }
-  `
-
-  const version_3_crashing = `
-  export function start(http, port, ctx) {
-    process.exit(1)
-  }
-  `
-
-  const version_4_stable = `
-  export function start(http, port, ctx) {
-    const server = http.createServer(function (req, res) {
-      res.writeHead(200);
-      res.end(JSON.stringify({ version: 'v4' }))
     })
-
-    return server.listenAsync(port, '0.0.0.0')
-      .then(() => {
-        ctx.log.info({ port: port, listening: true }, \`Server is listening on \${port} serving v4\`)
+  
+    const version_1_stable = `
+    export function start(http, port, ctx) {
+      const server = http.createServer(function (req, res) {
+        res.writeHead(200);
+        res.end(JSON.stringify({ version: 'v1' }))
       })
-  }
-  `
-
-  function file(relative) {
-    let file = util.getPathFromRoot(relative)
-    files.push(file)
-    return file
-  }
-
-  function log(message) {
-    let lines = message.split('\n')
-    for (let line of lines) {
-      if (!line.trim()) continue
-      logs.push(line)
+  
+      return server.listenAsync(port, '0.0.0.0')
+        .then(() => {
+          ctx.log.info({ port: port, listening: true }, \`Server is listening on \${port} serving v1\`)
+        })
     }
-  }
-
-  function parseLine(line) {
-    if (line[0] === '{') {
-      return JSON.parse(line)
+    `
+  
+    const version_2_nolisten = `
+    export function start(http, port, ctx) {
     }
-    return {
-      msg: line
+    `
+  
+    const version_3_crashing = `
+    export function start(http, port, ctx) {
+      process.exit(1)
     }
-  }
-
-
-  let logIndex = 0
-  function catchupLog(ms = 0) {
-    if (logs.length > logIndex) {
-      for (; logIndex < logs.length; logIndex++) {
-        prettyPrintMessage(logs[logIndex])
+    `
+  
+    const version_4_stable = `
+    export function start(http, port, ctx) {
+      const server = http.createServer(function (req, res) {
+        res.writeHead(200);
+        res.end(JSON.stringify({ version: 'v4' }))
+      })
+  
+      return server.listenAsync(port, '0.0.0.0')
+        .then(() => {
+          ctx.log.info({ port: port, listening: true }, \`Server is listening on \${port} serving v4\`)
+        })
+    }
+    `
+  
+    function file(relative) {
+      let file = util.getPathFromRoot(relative)
+      files.push(file)
+      return file
+    }
+  
+    function log(message) {
+      let lines = message.split('\n')
+      for (let line of lines) {
+        if (!line.trim()) continue
+        logs.push(line)
+        allLogs.push(line)
       }
     }
-    if (ms > 0) {
-      return setTimeout(ms)
+  
+    function parseLine(line) {
+      if (line[0] === '{') {
+        return JSON.parse(line)
+      }
+      return {
+        msg: line
+      }
     }
-  }
-
-  integrationLog.on('newlog', function(record) {
-    prettyPrintMessage(JSON.stringify(record))
-  })
-
-  let logWaitIndex = 0
-  function hasLogLine(regMatch) {
-    if (logs.length > logWaitIndex) {
-      for (; logWaitIndex < logs.length; logWaitIndex++) {
+  
+  
+    let logIndex = 0
+    function catchupLog(ms = 0) {
+      if (logs.length > logIndex) {
+        for (; logIndex < logs.length; logIndex++) {
+          if (turnDebuggingOn) {
+            prettyPrintMessage(logs[logIndex])
+          }
+        }
+      }
+      if (ms > 0) {
+        return setTimeout(ms)
+      }
+    }
+  
+    integrationLog.on('newlog', function(record) {
+      if (turnDebuggingOn) {
+        prettyPrintMessage(JSON.stringify(record))
+      }
+    })
+  
+    let logWaitIndex = 0
+    function hasLogLine(regMatch) {
+      if (logs.length > logWaitIndex) {
+        for (; logWaitIndex < logs.length; logWaitIndex++) {
+          if (typeof(regMatch) === 'function') {
+            let res = regMatch(parseLine(logs[logWaitIndex]))
+            if (res) return true
+          }
+          else if (logs[logWaitIndex].match(regMatch)) {
+            return true
+          }
+        }
+      }
+      return false
+    }
+    
+    function findInLogs(regMatch) {
+      for (let i = 0; i < logs.length; i++) {
         if (typeof(regMatch) === 'function') {
-          let res = regMatch(parseLine(logs[logWaitIndex]))
+          let res = regMatch(parseLine(logs[i]))
           if (res) return true
         }
-        else if (logs[logWaitIndex].match(regMatch)) {
+        else if (logs[i].match(regMatch)) {
           return true
         }
       }
     }
-    return false
-  }
   
-  function findInLogs(regMatch) {
-    for (let i = 0; i < logs.length; i++) {
-      if (typeof(regMatch) === 'function') {
-        let res = regMatch(parseLine(logs[i]))
-        if (res) return true
+    async function waitUntilListening() {
+      let listeningLine = null
+      while (processor.exitCode == null
+          && !hasLogLine((rec) => { listeningLine = rec; return rec.listening && rec.port })) {
+        await catchupLog(10)
       }
-      else if (logs[i].match(regMatch)) {
-        return true
-      }
-    }
-  }
-
-  async function waitUntilListening() {
-    let listeningLine = null
-    while (processor.exitCode == null
-        && !hasLogLine((rec) => { listeningLine = rec; return rec.listening && rec.port })) {
-      await catchupLog(10)
-    }
-    catchupLog()
-    if (listeningLine.listening && listeningLine.port) {
-      return listeningLine 
-    } else {
-      return null
-    }
-  }
-
-  async function waitUntilClosed(listening) {
-    while (true) {
       catchupLog()
-      try {
-        await request({}, `http://localhost:${listening.port}/`)
-      } catch (err) {
-        break
+      if (listeningLine.listening && listeningLine.port) {
+        return listeningLine 
+      } else {
+        return null
       }
-      await setTimeout(25)
-    }
-    catchupLog()
-
-    logs.splice(0, logs.length); logIndex = 0; logWaitIndex = 0; console.log('\n-------\n')
-  }
-
-  function startRunner() {
-    return util.runCommandBackground('node', ['runner.mjs'], util.getPathFromRoot('./'), log)
-  }
-
-  t.test('should be fully operational', async function() {
-    console.log()
-
-    let index = file('./index.mjs')
-    await fs.writeFile(index, version_1_stable)
-    await util.runCommand(compressorPath, ['a', file('./v1-sc.7z'), index], util.getPathFromRoot('./testapp'))
-
-    processor = startRunner()
-
-
-    while (processor.exitCode == null) {
-      await catchupLog(10)
     }
 
-    catchupLog()
-
-    let secondLast = parseLine(logs[logs.length - 2])
-    let last = parseLine(logs[logs.length - 1])
-    assert.match(secondLast.msg, /creating/i)
-    assert.match(secondLast.msg, /application/i)
-    assert.match(secondLast.msg, /testapp/i)
-    assert.match(secondLast.msg, /0 releases/i)
-    assert.match(last.err.message, /none/i)
-    assert.match(last.err.message, /successful/i)
-
-    // Reset our log
-    logs.splice(0, logs.length); logIndex = 0; logWaitIndex = 0; console.log('\n-------\n')
-
-    const assertNameVersion1 = 'v1_ok'
-
-    file(`./testapp/${assertNameVersion1}`)
-
-    versions.splice(0, 0, [assertNameVersion1, 'ok version', 'v1-sc.7z'])
-    processor = startRunner()
-
-    let listening = await waitUntilListening()
-
-    let checkListening = await request({}, `http://localhost:${listening.port}/`)
-    assert.strictEqual(checkListening.body.version, 'v1')
-
-    while (!hasLogLine(/core is running/)) {
-      await catchupLog(10)
+    async function sendRequestToApplication(listening) {
+      let lastErr = null
+      for (let i = 0; i < 3; i++) {
+        try {
+          let checkListening = await request({}, `http://localhost:${listening.port}/`)
+          return checkListening
+        } catch (err) {
+          lastErr = err
+          await setTimeout(150)
+        }
+      }
+      log('-- core.test.integration.mjs crash here --')
+      log(lastErr.toString())
+      throw lastErr
     }
-
-    catchupLog()
-
-    let db = JSON.parse(await fs.readFile(util.getPathFromRoot('./db.json')))
-    assert.strictEqual(db.core.testapp.active, assertNameVersion1)
-    assert.strictEqual(db.core.testapp.versions.length, 1)
-    assert.strictEqual(db.core.testapp.versions[0].stable, 1)
-    assert.strictEqual(db.core.testapp.versions[0].installed, true)
-
-    // Create our second version
-    await fs.writeFile(index, version_2_nolisten)
-    await util.runCommand(compressorPath, ['a', file('./v2-sc.7z'), index], util.getPathFromRoot('./testapp'))
-    
-    const assertNameVersion2 = 'v2_nolisten'
-    file(`./testapp/${assertNameVersion2}`)
-    versions.splice(0, 0, [assertNameVersion2, 'no listen version', 'v2-sc.7z'])
-
-    // wait a second for it to trigger an update
-
-    await setTimeout(500)
-
-    while (!hasLogLine(/Error starting v2_nolisten/)) {
-      await catchupLog(10)
+  
+    async function waitUntilClosed(listening) {
+      while (true) {
+        catchupLog()
+        try {
+          await request({}, `http://localhost:${listening.port}/`)
+        } catch (err) {
+          break
+        }
+        await setTimeout(25)
+      }
+      catchupLog()
+  
+      logs.splice(0, logs.length); logIndex = 0; logWaitIndex = 0;
+      if (turnDebuggingOn) { console.log('\n-------\n') }
     }
-    while (!hasLogLine(/restart request.*v2_nolisten.*dirty/)) {
-      await catchupLog(10)
+  
+    function startRunner() {
+      return util.runCommandBackground('node', [runnerName], util.getPathFromRoot('./'), log)
     }
-    while (processor.exitCode == null) {
-      await catchupLog(10)
-    }
-    catchupLog()
+  
+    t.test('should be fully operational', async function() {
+      console.log()
+      if (!turnDebuggingOn) { console.log('Running empty test') }
 
-    db = JSON.parse(await fs.readFile(util.getPathFromRoot('./db.json')))
-    assert.strictEqual(db.core.testapp.active, assertNameVersion2)
-    assert.strictEqual(db.core.testapp.versions.length, 2)
-    assert.strictEqual(db.core.testapp.versions[0].stable, -1)
-    assert.strictEqual(db.core.testapp.versions[0].installed, true)
-    assert.strictEqual(db.core.testapp.versions[1].stable, 1)
-    assert.strictEqual(db.core.testapp.versions[1].installed, true)
+      let index = file('./index.mjs')
+      await fs.writeFile(index, version_1_stable)
+      await util.runCommand(compressorPath, ['a', file('./v1-sc.7z'), index], util.getPathFromRoot('./testapp'))
 
-    // Since application was in dirty state, on next attempt should attempt to
-    // run v2 again and then falling back to v1
+      processor = startRunner()
 
-    await waitUntilClosed()
-    processor = startRunner()
-    await catchupLog(10)
 
-    while (!hasLogLine(/Attempting to run version v2_nolisten/)) {
-      await catchupLog(10)
-    }
-    while (!hasLogLine(/Attempting to run version v1_ok/)) {
-      await catchupLog(10)
-    }
-    
-    listening = await waitUntilListening()
-    assert.ok(listening)
-    checkListening = await request({}, `http://localhost:${listening.port}/`)
-    assert.strictEqual(checkListening.body.version, 'v1')
-    
-    while (!hasLogLine(/core is running/)) {
+      while (processor.exitCode == null) {
+        await catchupLog(10)
+      }
+
+      catchupLog()
+
+      let secondLast = parseLine(logs[logs.length - 2])
+      let last = parseLine(logs[logs.length - 1])
+      assert.match(secondLast.msg, /creating/i)
+      assert.match(secondLast.msg, /application/i)
+      assert.match(secondLast.msg, /testapp/i)
+      assert.match(secondLast.msg, /0 releases/i)
+      assert.match(last.err.message, /none/i)
+      assert.match(last.err.message, /successful/i)
+
+      // Reset our log
+      logs.splice(0, logs.length); logIndex = 0; logWaitIndex = 0;
+      if (turnDebuggingOn) { console.log('\n-------\n') }
+
+      const assertNameVersion1 = 'v1_ok'
+
+      if (!turnDebuggingOn) { console.log(`Running update ${assertNameVersion1} test`) }
+
+      file(`./testapp/${assertNameVersion1}`)
+
+      versions.splice(0, 0, [assertNameVersion1, 'ok version', 'v1-sc.7z'])
+      processor = startRunner()
+
+      let listening = await waitUntilListening()
+
+      let checkListening = await sendRequestToApplication(listening)
+      assert.strictEqual(checkListening.body.version, 'v1')
+
+      while (!hasLogLine(/core is running/)) {
+        await catchupLog(10)
+        if (processor.exitCode !== null) {
+          throw new Error('Process exited with ' + processor.exitCode)
+        }
+      }
+
+      catchupLog()
+
+      let db = JSON.parse(await fs.readFile(util.getPathFromRoot('./db.json')))
+      assert.strictEqual(db.core[appname].active, assertNameVersion1)
+      assert.strictEqual(db.core[appname].versions.length, 1)
+      assert.strictEqual(db.core[appname].versions[0].stable, 1)
+      assert.strictEqual(db.core[appname].versions[0].installed, true)
+
+      // Create our second version
+      await fs.writeFile(index, version_2_nolisten)
+      await util.runCommand(compressorPath, ['a', file('./v2-sc.7z'), index], util.getPathFromRoot('./testapp'))
+      
+      const assertNameVersion2 = 'v2_nolisten'
+      if (!turnDebuggingOn) { console.log(`Running update ${assertNameVersion2} test`) }
+      file(`./testapp/${assertNameVersion2}`)
+      versions.splice(0, 0, [assertNameVersion2, 'no listen version', 'v2-sc.7z'])
+
+      // wait a second for it to trigger an update
+
+      await setTimeout(500)
+
+      while (!hasLogLine(/Error starting v2_nolisten/)) {
+        await catchupLog(10)
+      }
+
+      if (appname !== 'testappcluster') {
+        while (!hasLogLine(/restart request.*v2_nolisten.*dirty/)) {
+          await catchupLog(10)
+        }
+
+        while (processor.exitCode == null) {
+          await catchupLog(10)
+        }
+        catchupLog()
+
+        db = JSON.parse(await fs.readFile(util.getPathFromRoot('./db.json')))
+        assert.strictEqual(db.core[appname].active, assertNameVersion2)
+        assert.strictEqual(db.core[appname].versions.length, 2)
+        assert.strictEqual(db.core[appname].versions[0].stable, -1)
+        assert.strictEqual(db.core[appname].versions[0].installed, true)
+        assert.strictEqual(db.core[appname].versions[1].stable, 1)
+        assert.strictEqual(db.core[appname].versions[1].installed, true)
+
+        // Since application was in dirty state, on next attempt should attempt to
+        // run v2 again and then falling back to v1
+
+        await waitUntilClosed()
+        
+        if (!turnDebuggingOn) { console.log(`Running fresh ${assertNameVersion2} test`) }
+        processor = startRunner()
+        await catchupLog(10)
+
+        while (!hasLogLine(/Attempting to run version v2_nolisten/)) {
+          await catchupLog(10)
+        }
+      }
+
+      while (!hasLogLine(/Attempting to run version v1_ok/)) {
+        await catchupLog(10)
+      }
+      
+      listening = await waitUntilListening()
+      assert.ok(listening)
+      checkListening = await sendRequestToApplication(listening)
+      assert.strictEqual(checkListening.body.version, 'v1')
+      
+      while (!hasLogLine(/is up and running/)) {
+        await setTimeout(10)
+      }
+
+      db = JSON.parse(await fs.readFile(util.getPathFromRoot('./db.json')))
+      assert.strictEqual(db.core[appname].active, assertNameVersion1)
+      assert.strictEqual(db.core[appname].versions.length, 2)
+      assert.strictEqual(db.core[appname].versions[0].stable, -2)
+      assert.strictEqual(db.core[appname].versions[1].stable, 1)
+
+      assert.ok(findInLogs(/Attempting to run version v2_nolisten/))
+      assert.ok(findInLogs(/Error starting v2_nolisten/))
+
+      processor.kill()
+
+      if (!turnDebuggingOn) { console.log(`Running version stability check test`) }
+
+      await waitUntilClosed()
+      processor = startRunner()
+
+      listening = await waitUntilListening()
+
+      assert.ok(listening)
+
+      checkListening = await sendRequestToApplication(listening)
+      assert.strictEqual(checkListening.body.version, 'v1')
+      
+      while (!hasLogLine(/is up and running/)) {
+        await setTimeout(10)
+      }
+
+      db = JSON.parse(await fs.readFile(util.getPathFromRoot('./db.json')))
+      assert.strictEqual(db.core[appname].active, assertNameVersion1)
+      assert.strictEqual(db.core[appname].versions.length, 2)
+      assert.strictEqual(db.core[appname].versions[0].stable, -2)
+      assert.strictEqual(db.core[appname].versions[1].stable, 1)
+
+      assert.notOk(findInLogs(/Attempting to run version v2_nolisten/))
+      assert.notOk(findInLogs(/Error starting v2_nolisten/))
+      
+      // Create our third version
+      await fs.writeFile(index, version_3_crashing)
+      await util.runCommand(compressorPath, ['a', file('./v3-sc.7z'), index], util.getPathFromRoot('./testapp'))
+      
+      const assertNameVersion3 = 'v3_crash'
+      if (!turnDebuggingOn) { console.log(`Running update ${assertNameVersion3} test`) }
+      file(`./testapp/${assertNameVersion3}`)
+      versions.splice(0, 0, [assertNameVersion3, 'crash version', 'v3-sc.7z'])
+
+      // wait a second for it to trigger an update
+
+      await setTimeout(500)
+
+      while (!hasLogLine(/Attempting to run version v3_crash/)) {
+        await catchupLog(10)
+      }
+      
+      if (appname !== 'testappcluster') {
+        while (processor.exitCode == null) {
+          await catchupLog(10)
+        }
+
+        db = JSON.parse(await fs.readFile(util.getPathFromRoot('./db.json')))
+        assert.strictEqual(db.core[appname].active, assertNameVersion3)
+        assert.strictEqual(db.core[appname].versions.length, 3)
+        assert.strictEqual(db.core[appname].versions[0].stable, -2)
+        assert.strictEqual(db.core[appname].versions[1].stable, -2)
+        assert.strictEqual(db.core[appname].versions[2].stable, 1)
+
+        catchupLog()
+
+        // Should recover afterwards
+        await waitUntilClosed()
+        processor = startRunner()
+
+        listening = await waitUntilListening()
+
+        assert.ok(listening)
+
+        checkListening = await sendRequestToApplication(listening)
+        assert.strictEqual(checkListening.body.version, 'v1')
+        
+        while (!hasLogLine(/core is running/)) {
+          await setTimeout(10)
+        }
+      } else {
+        while (!hasLogLine(/Attempting to run version v1_ok/)) {
+          await catchupLog(10)
+        }
+        while (!hasLogLine(/is up and running/)) {
+          await setTimeout(10)
+        }
+        
+        db = JSON.parse(await fs.readFile(util.getPathFromRoot('./db.json')))
+        assert.strictEqual(db.core[appname].active, assertNameVersion1)
+        assert.strictEqual(db.core[appname].versions.length, 3)
+        assert.strictEqual(db.core[appname].versions[0].stable, -2)
+        assert.strictEqual(db.core[appname].versions[1].stable, -2)
+        assert.strictEqual(db.core[appname].versions[2].stable, 1)
+      }
+
+      // Create our fourth version
+      await fs.writeFile(index, version_4_stable)
+      await util.runCommand(compressorPath, ['a', file('./v4-sc.7z'), index], util.getPathFromRoot('./testapp'))
+      
+      const assertNameVersion4 = 'v4_stable'
+      if (!turnDebuggingOn) { console.log(`Running update ${assertNameVersion4} test`) }
+      file(`./testapp/${assertNameVersion4}`)
+      versions.splice(0, 0, [assertNameVersion4, 'no listen version', 'v4-sc.7z'])
+
+      // wait a second for it to trigger an update
+
+      await setTimeout(500)
+
+      while (!hasLogLine(/Attempting to run version v4_stable/)) {
+        await catchupLog(10)
+      }
+
+      while (!hasLogLine(/Server is listening on 31313 serving v4/)) {
+        await catchupLog(10)
+      }
+
+      catchupLog()
+
+      checkListening = await sendRequestToApplication(listening)
+      assert.strictEqual(checkListening.body.version, 'v4')
+
       await setTimeout(10)
-    }
-
-    db = JSON.parse(await fs.readFile(util.getPathFromRoot('./db.json')))
-    assert.strictEqual(db.core.testapp.active, assertNameVersion1)
-    assert.strictEqual(db.core.testapp.versions.length, 2)
-    assert.strictEqual(db.core.testapp.versions[0].stable, -2)
-    assert.strictEqual(db.core.testapp.versions[1].stable, 1)
-
-    assert.ok(findInLogs(/Attempting to run version v2_nolisten/))
-    assert.ok(findInLogs(/Error starting v2_nolisten/))
-
-    processor.kill()
-
-    await waitUntilClosed()
-    processor = startRunner()
-
-    listening = await waitUntilListening()
-
-    assert.ok(listening)
-
-    checkListening = await request({}, `http://localhost:${listening.port}/`)
-    assert.strictEqual(checkListening.body.version, 'v1')
-    
-    while (!hasLogLine(/core is running/)) {
-      await setTimeout(10)
-    }
-
-    db = JSON.parse(await fs.readFile(util.getPathFromRoot('./db.json')))
-    assert.strictEqual(db.core.testapp.active, assertNameVersion1)
-    assert.strictEqual(db.core.testapp.versions.length, 2)
-    assert.strictEqual(db.core.testapp.versions[0].stable, -2)
-    assert.strictEqual(db.core.testapp.versions[1].stable, 1)
-
-    assert.notOk(findInLogs(/Attempting to run version v2_nolisten/))
-    assert.notOk(findInLogs(/Error starting v2_nolisten/))
-    
-    // Create our third version
-    await fs.writeFile(index, version_3_crashing)
-    await util.runCommand(compressorPath, ['a', file('./v3-sc.7z'), index], util.getPathFromRoot('./testapp'))
-    
-    const assertNameVersion3 = 'v3_crash'
-    file(`./testapp/${assertNameVersion3}`)
-    versions.splice(0, 0, [assertNameVersion3, 'crash version', 'v3-sc.7z'])
-
-    // wait a second for it to trigger an update
-
-    await setTimeout(500)
-
-    while (!hasLogLine(/Attempting to run version v3_crash/)) {
-      await catchupLog(10)
-    }
-    
-    while (processor.exitCode == null) {
-      await catchupLog(10)
-    }
-
-    db = JSON.parse(await fs.readFile(util.getPathFromRoot('./db.json')))
-    assert.strictEqual(db.core.testapp.active, assertNameVersion3)
-    assert.strictEqual(db.core.testapp.versions.length, 3)
-    assert.strictEqual(db.core.testapp.versions[0].stable, -2)
-    assert.strictEqual(db.core.testapp.versions[1].stable, -2)
-    assert.strictEqual(db.core.testapp.versions[2].stable, 1)
-
-    catchupLog()
-
-    // Should recover afterwards
-    await waitUntilClosed()
-    processor = startRunner()
-
-    listening = await waitUntilListening()
-
-    assert.ok(listening)
-
-    checkListening = await request({}, `http://localhost:${listening.port}/`)
-    assert.strictEqual(checkListening.body.version, 'v1')
-    
-    while (!hasLogLine(/core is running/)) {
-      await setTimeout(10)
-    }
-
-    // Create our fourth version
-    await fs.writeFile(index, version_4_stable)
-    await util.runCommand(compressorPath, ['a', file('./v4-sc.7z'), index], util.getPathFromRoot('./testapp'))
-    
-    const assertNameVersion4 = 'v4_stable'
-    file(`./testapp/${assertNameVersion4}`)
-    versions.splice(0, 0, [assertNameVersion4, 'no listen version', 'v4-sc.7z'])
-
-    // wait a second for it to trigger an update
-
-    await setTimeout(500)
-
-    while (!hasLogLine(/Attempting to run version v4_stable/)) {
-      await catchupLog(10)
-    }
-
-    while (!hasLogLine(/Server is listening on 31313 serving v4/)) {
-      await catchupLog(10)
-    }
-
-    catchupLog()
-
-    checkListening = await request({}, `http://localhost:${listening.port}/`)
-    assert.strictEqual(checkListening.body.version, 'v4')
-
-    await setTimeout(10)
-    
-    db = JSON.parse(await fs.readFile(util.getPathFromRoot('./db.json')))
-    assert.strictEqual(db.core.testapp.active, assertNameVersion4)
-    assert.strictEqual(db.core.testapp.versions.length, 4)
-    assert.strictEqual(db.core.testapp.versions[0].stable, 1)
-    assert.strictEqual(db.core.testapp.versions[1].stable, -2)
+      
+      db = JSON.parse(await fs.readFile(util.getPathFromRoot('./db.json')))
+      assert.strictEqual(db.core[appname].active, assertNameVersion4)
+      assert.strictEqual(db.core[appname].versions.length, 4)
+      assert.strictEqual(db.core[appname].versions[0].stable, 1)
+      assert.strictEqual(db.core[appname].versions[1].stable, -2)
+      wasSuccessful = true
+    })
   })
 })
diff --git a/test/core.test.mjs b/test/core.test.mjs
index 71b6536..0c8a1be 100644
--- a/test/core.test.mjs
+++ b/test/core.test.mjs
@@ -239,6 +239,7 @@ t.describe('#constructor()', function() {
     assert.strictEqual(core.restart, assertRestarter)
     assert.deepStrictEqual(core.applications, [])
     assert.ok(core.applicationMap)
+    assert.strictEqual(core.isSlave, false)
   })
 })
 
@@ -965,7 +966,6 @@ t.describe('#runApplication()', function() {
     assert.notStrictEqual(err, assertError)
     assert.match(err.message, /found/)
   })
-  
 
   t.test('should throw if no version are found', async function() {
     const assertError = new Error('Daikichi to Rin')
@@ -1016,7 +1016,6 @@ t.describe('#runApplication()', function() {
     assert.ok(stubWrite.called)
   })
   
-  
   t.test('should succeed if running a minus one on fresh', async function() {
     const assertError = new Error('Daikichi to Rin')
     let count = 0
diff --git a/test/helpers.mjs b/test/helpers.mjs
index 233b7d0..5f6b608 100644
--- a/test/helpers.mjs
+++ b/test/helpers.mjs
@@ -77,7 +77,7 @@ export function prettyPrintMessage(line) {
   if (line[0] === '{') {
     try {
       let rec = JSON.parse(line)
-      console.log(`[${rec.time.substr(11).replace('Z', '')}] ${style(levels[rec.level], levelcolor[rec.level])}: ${rec.name}: ${style(rec.msg, 'cyan')}`)
+      console.log(`[${rec.time.substr(11).replace('Z', '')}] ${style(levels[rec.level], levelcolor[rec.level])}: ${rec.name} ${style('(pid: ' + rec.pid + ')', 'grey')}: ${style(rec.msg, 'cyan')}`)
       if (rec.err && rec.err.message && rec.err.stack) {
         let err = new Error(rec.err.message)
         err.stack = rec.err.stack
diff --git a/test/runner_cluster.mjs b/test/runner_cluster.mjs
new file mode 100644
index 0000000..c8a501c
--- /dev/null
+++ b/test/runner_cluster.mjs
@@ -0,0 +1,36 @@
+import fs from 'fs'
+import cluster from 'cluster'
+import { runner } from '../core/runner.mjs'
+
+if (cluster.isPrimary) {
+  try {
+    fs.rmSync(util.getPathFromRoot('./db.json'))
+  } catch {}
+}
+
+runner(import.meta.url, {
+  name: 'test-runner-cluster',
+  testappcluster: {
+    cluster: 2,
+    port: 31313,
+    provider: 'git',
+    url: 'http://localhost:61412/releases',
+    updateEvery: 0.014,
+    heartbeatTimeout: 100,
+    heartbeatAttempts: 3,
+    heartbeatAttemptsWait: 100,
+    log: [{
+      stream: 'process.stdout',
+      level: 'info',
+    }],
+  }
+}, 'db.json')
+.then(
+  function(core) {
+    core.log.info('core is running')
+  },
+  function(err) {
+    runner.log.error(err, 'Error starting runner')
+    process.exit(1)
+  }
+)
diff --git a/test/util.test.mjs b/test/util.test.mjs
index 09db98b..e31ceea 100644
--- a/test/util.test.mjs
+++ b/test/util.test.mjs
@@ -195,6 +195,35 @@ t.describe('#getApplications()', function() {
     assert.deepStrictEqual(util.getAppNames(getBase({ heartbeatAttemptsWait: {} })), [])
   })
 
+  t.test('should fail to find if clusterWaitOnCrash is defined but not a valid number', function() {
+    assert.deepStrictEqual(util.getAppNames(getBase()), ['app'])
+    assert.deepStrictEqual(util.getAppNames(getBase({ clusterWaitOnCrash: null })), ['app'])
+    assert.deepStrictEqual(util.getAppNames(getBase({ clusterWaitOnCrash: 5 })), [])
+    assert.deepStrictEqual(util.getAppNames(getBase({ clusterWaitOnCrash: 15 })), ['app'])
+    assert.deepStrictEqual(util.getAppNames(getBase({ clusterWaitOnCrash: 1000 })), ['app'])
+    assert.deepStrictEqual(util.getAppNames(getBase({ clusterWaitOnCrash: 'asdf' })), [])
+    assert.deepStrictEqual(util.getAppNames(getBase({ clusterWaitOnCrash: '1234' })), [])
+    assert.deepStrictEqual(util.getAppNames(getBase({ clusterWaitOnCrash: 0 })), [])
+    assert.deepStrictEqual(util.getAppNames(getBase({ clusterWaitOnCrash: -5 })), [])
+    assert.deepStrictEqual(util.getAppNames(getBase({ clusterWaitOnCrash: [] })), [])
+    assert.deepStrictEqual(util.getAppNames(getBase({ clusterWaitOnCrash: {} })), [])
+  })
+
+  t.test('should fail to find if cluster is defined but not a valid number', function() {
+    assert.deepStrictEqual(util.getAppNames(getBase()), ['app'])
+    assert.deepStrictEqual(util.getAppNames(getBase({ cluster: null })), ['app'])
+    assert.deepStrictEqual(util.getAppNames(getBase({ cluster: 1 })), ['app'])
+    assert.deepStrictEqual(util.getAppNames(getBase({ cluster: 5 })), ['app'])
+    assert.deepStrictEqual(util.getAppNames(getBase({ cluster: 15 })), ['app'])
+    assert.deepStrictEqual(util.getAppNames(getBase({ cluster: 1000 })), [])
+    assert.deepStrictEqual(util.getAppNames(getBase({ cluster: 'asdf' })), [])
+    assert.deepStrictEqual(util.getAppNames(getBase({ cluster: '1234' })), [])
+    assert.deepStrictEqual(util.getAppNames(getBase({ cluster: 0 })), ['app'])
+    assert.deepStrictEqual(util.getAppNames(getBase({ cluster: -5 })), [])
+    assert.deepStrictEqual(util.getAppNames(getBase({ cluster: [] })), [])
+    assert.deepStrictEqual(util.getAppNames(getBase({ cluster: {} })), [])
+  })
+
   t.test('should fail to find if heartbeatPath is defined but not a valid string', function() {
     assert.deepStrictEqual(util.getAppNames(getBase()), ['app'])
     assert.deepStrictEqual(util.getAppNames(getBase({ heartbeatPath: null })), ['app'])