initial commit

14 files changed, 1868 insertions, 0 deletions

diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..7a1537b
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,2 @@
+.idea
+node_modules
diff --git a/README.md b/README.md
new file mode 100644
index 0000000..7354f91
--- /dev/null
+++ b/README.md
@@ -0,0 +1,44 @@
+# jobd
+
+**jobd** is a simple job queue daemon written in Node.JS. It uses MySQL
+table as a storage.
+
+
+## Installation
+
+To be written
+
+
+## Usage
+
+To be written
+
+
+## MySQL setup
+
+Table scheme. You can add additional fields if you need.
+
+```
+CREATE TABLE `jobs` (
+  `id` int(10) UNSIGNED NOT NULL AUTO_INCREMENT,
+  `target` char(16) NOT NULL,
+  `slot` char(16) DEFAULT NULL,
+  `time_created` int(10) UNSIGNED NOT NULL,
+  `time_started` int(10) UNSIGNED NOT NULL DEFAULT 0,
+  `time_finished` int(10) UNSIGNED NOT NULL DEFAULT 0,
+  `status` enum('waiting','manual','accepted','running','done','ignored') NOT NULL DEFAULT 'waiting',
+  `result` enum('ok','fail') DEFAULT NULL,
+  `return_code` tinyint(3) UNSIGNED DEFAULT NULL,
+  `sig` char(10) DEFAULT NULL,
+  `stdout` mediumtext DEFAULT NULL,
+  `stderr` mediumtext DEFAULT NULL,
+  PRIMARY KEY (`id`),
+  KEY `status_target_idx` (`status`, `target`, `id`)
+) ENGINE=InnoDB DEFAULT CHARSET=utf8;
+```
+
+You can turn `target` and `slot` to `ENUM`, for optimization.
+
+## License
+
+BSD-2c
\ No newline at end of file
diff --git a/jobd-master.conf.example b/jobd-master.conf.example
new file mode 100644
index 0000000..48819d8
--- /dev/null
+++ b/jobd-master.conf.example
@@ -0,0 +1,12 @@
+; server settings
+host = 0.0.0.0
+port = 13597
+;password =
+
+ping_interval = 30 ; seconds
+poke_throttle_interval = 0.5 ; seconds
+
+; logging
+log_file = /tmp/jobd-master.log
+log_level_file = info
+log_level_console = debug
diff --git a/jobd.conf.example b/jobd.conf.example
new file mode 100644
index 0000000..0659018
--- /dev/null
+++ b/jobd.conf.example
@@ -0,0 +1,38 @@
+; server settings
+host = 0.0.0.0
+port = 13596
+;password =
+
+master_host = 127.0.0.1
+master_port = 13597
+master_reconnect_timeout = 10
+
+; log
+log_file = /tmp/jobd.log
+log_level_file = info
+log_level_console = debug
+
+; mysql settings
+mysql_host = 10.211.55.6
+mysql_port = 3306
+mysql_user = jobd
+mysql_password = password
+mysql_database = jobd
+mysql_table = jobs
+mysql_fetch_limit = 10
+
+; launcher command template
+launcher = php /Users/ch1p/jobd-launcher.php --id {id}
+max_output_buffer = 16777216
+
+;
+; targets
+;
+
+[server1]
+low = 5
+normal = 5
+high = 5
+
+[global]
+normal = 3
\ No newline at end of file
diff --git a/package.json b/package.json
new file mode 100644
index 0000000..a1b4220
--- /dev/null
+++ b/package.json
@@ -0,0 +1,34 @@
+{
+  "name": "jobd",
+  "version": "1.0.0",
+  "description": "job queue daemon",
+  "main": "src/jobd",
+  "homepage": "https://github.com/gch1p/jobd#readme",
+  "bugs": {
+    "url" : "https://github.com/gch1p/jobd/issues",
+    "email": "me@ch1p.io"
+  },
+  "scripts": {
+    "test": "echo \"Error: no test specified\" && exit 1"
+  },
+  "bin": {
+    "jobd": "./src/jobd.js",
+    "jobd-master": "./src/jobd-master.js"
+  },
+  "keywords": [],
+  "author": "Evgeny Zinoviev",
+  "license": "BSD-2-Clause",
+  "os": [
+    "darwin",
+    "linux"
+  ],
+  "dependencies": {
+    "ini": "^2.0.0",
+    "lodash": "^4.17.21",
+    "log4js": "^6.3.0",
+    "minimist": "^1.2.5",
+    "mysql": "^2.18.1",
+    "promise-mysql": "^5.0.2",
+    "queue": "^6.0.2"
+  }
+}
diff --git a/src/config.js b/src/config.js
new file mode 100644
index 0000000..9ee6338
--- /dev/null
+++ b/src/config.js
@@ -0,0 +1,119 @@
+const fs = require('fs')
+const ini = require('ini')
+const {isNumeric} = require('./util')
+
+let workerConfig = {
+    targets: {},
+}
+let masterConfig = {}
+
+function readFile(file) {
+    if (!fs.existsSync(file))
+        throw new Error(`file ${file} not found`)
+
+    return ini.parse(fs.readFileSync(file, 'utf-8'))
+}
+
+function processScheme(source, scheme) {
+    const result = {}
+    
+    for (let key in scheme) {
+        let opts = scheme[key]
+        let ne = !(key in source) || !source[key]
+        if (opts.required === true && ne)
+            throw new Error(`'${key}' is not defined`)
+
+        let value = source[key] ?? opts.default ?? null
+
+        switch (opts.type) {
+            case 'int':
+                if (!isNumeric(value))
+                    throw new Error(`'${key}' must be an integer`)
+                value = parseInt(value, 10)
+                break
+
+            case 'float':
+                if (!isNumeric(value))
+                    throw new Error(`'${key}' must be a float`)
+                value = parseFloat(value)
+                break
+        }
+
+        result[key] = value
+    }
+    
+    return result
+}
+
+function parseWorkerConfig(file) {
+    const raw = readFile(file)
+
+    const scheme = {
+        host:     {required: true},
+        port:     {required: true, type: 'int'},
+        password: {},
+
+        master_host: {},
+        master_port: {type: 'int', default: 0},
+        master_reconnect_timeout: {type: 'int', default: 10},
+
+        log_file:          {},
+        log_level_file:    {default: 'warn'},
+        log_level_console: {default: 'warn'},
+
+        mysql_host:        {required: true},
+        mysql_port:        {required: true, type: 'int'},
+        mysql_user:        {required: true},
+        mysql_password:    {required: true},
+        mysql_database:    {required: true},
+        mysql_table:       {required: true, default: 'jobs'},
+        mysql_fetch_limit: {default: 100, type: 'int'},
+
+        launcher:          {required: true},
+        max_output_buffer: {default: 1024*1024, type: 'int'},
+    }
+    Object.assign(workerConfig, processScheme(raw, scheme))
+
+    // targets
+    for (let target in raw) {
+        if (target === 'null')
+            throw new Error('word \'null\' is reserved, please don\'t use it as a target name')
+
+        if (typeof raw[target] !== 'object')
+            continue
+
+        workerConfig.targets[target] = {slots: {}}
+        for (let slotName in raw[target]) {
+            let slotLimit = parseInt(raw[target][slotName], 10)
+            if (slotLimit < 1)
+                throw new Error(`${target}: slot ${slotName} has invalid limit`)
+            workerConfig.targets[target].slots[slotName] = slotLimit
+        }
+    }
+}
+
+function parseMasterConfig(file) {
+    const raw = readFile(file)
+
+    const scheme = {
+        host:     {required: true},
+        port:     {required: true, type: 'int'},
+        password: {},
+
+        ping_interval:          {default: 30, type: 'int'},
+        poke_throttle_interval: {default: 0.5, type: 'float'},
+
+        log_file:          {},
+        log_level_file:    {default: 'warn'},
+        log_level_console: {default: 'warn'},
+    }
+    Object.assign(masterConfig, processScheme(raw, scheme))
+}
+
+module.exports = {
+    parseWorkerConfig,
+    parseMasterConfig,
+
+    workerConfig,
+    masterConfig
+}
\ No newline at end of file
diff --git a/src/db.js b/src/db.js
new file mode 100644
index 0000000..0ffba84
--- /dev/null
+++ b/src/db.js
@@ -0,0 +1,49 @@
+const {workerConfig} = require('./config')
+const {getLogger} = require('./logger')
+const mysql = require('promise-mysql')
+
+let link
+const logger = getLogger('db')
+
+async function init() {
+    link = await mysql.createConnection({
+        host: workerConfig.mysql_host,
+        user: workerConfig.mysql_user,
+        password: workerConfig.mysql_password,
+        database: workerConfig.mysql_database
+    })
+}
+
+function wrap(method, isAsync = true, log = true) {
+    return isAsync ? async function(...args) {
+        if (log)
+            logger.trace(`${method}: `, args)
+
+        try {
+            return await link[method](...args)
+        } catch (error) {
+            logger.error(`db.${method}:`, error, link)
+
+            if (       error.code === 'PROTOCOL_ENQUEUE_AFTER_FATAL_ERROR'
+                    || error.code === 'PROTOCOL_CONNECTION_LOST'
+                    || error.fatal === true) {
+                // try to reconnect and call it again, once
+                await init()
+                return await link[method](...args)
+            }
+        }
+    } : function(...args) {
+        if (log)
+            logger.trace(`${method}: `, args)
+
+        return link[method](...args)
+    }
+}
+
+module.exports = {
+    init,
+    query: wrap('query'),
+    beginTransaction: wrap('beginTransaction'),
+    commit: wrap('commit'),
+    escape: wrap('escape', false, false)
+}
\ No newline at end of file
diff --git a/src/jobd-master.js b/src/jobd-master.js
new file mode 100755
index 0000000..0c33942
--- /dev/null
+++ b/src/jobd-master.js
@@ -0,0 +1,153 @@
+#!/usr/bin/env node
+const minimist = require('minimist')
+const loggerModule = require('./logger')
+const configModule = require('./config')
+const {Server, ResponseMessage, RequestMessage} = require('./server')
+const WorkersList = require('./workers-list')
+const {masterConfig} = configModule
+
+
+/**
+ * @type {Logger}
+ */
+let logger
+
+/**
+ * @type {Server}
+ */
+let server
+
+/**
+ * @type WorkersList
+ */
+let workers
+
+
+main().catch(e => {
+    console.error(e)
+    process.exit(1)
+})
+
+
+async function main() {
+    if (process.argv.length < 3) {
+        usage()
+        process.exit(0)
+    }
+
+    process.on('SIGINT', term)
+    process.on('SIGTERM', term)
+
+    const argv = minimist(process.argv.slice(2))
+    if (!argv.config)
+        throw new Error('--config option is required')
+
+    // read config
+    try {
+        configModule.parseMasterConfig(argv.config)
+    } catch (e) {
+        console.error(`config parsing error: ${e.message}`)
+        process.exit(1)
+    }
+
+    await loggerModule.init({
+        file: masterConfig.log_file,
+        levelFile: masterConfig.log_level_file,
+        levelConsole: masterConfig.log_level_console,
+    })
+    logger = loggerModule.getLogger('jobd-master')
+
+    // console.log(masterConfig)
+
+    workers = new WorkersList()
+
+    // start server
+    server = new Server()
+    server.on('message', onMessage)
+    server.start(masterConfig.port, masterConfig.host)
+    logger.info('server started')
+}
+
+/**
+ * @param {RequestMessage|ResponseMessage} message
+ * @param {Connection} connection
+ * @return {Promise<*>}
+ */
+async function onMessage({message, connection}) {
+    try {
+        if (!(message instanceof RequestMessage)) {
+            logger.debug('ignoring message', message)
+            return
+        }
+
+        if (message.requestType !== 'ping')
+            logger.info('onMessage:', message)
+
+        if (masterConfig.password && message.password !== masterConfig.password) {
+            connection.send(new ResponseMessage().setError('invalid password'))
+            return connection.close()
+        }
+
+        switch (message.requestType) {
+            case 'ping':
+                connection.send(new ResponseMessage().setError('pong'))
+                break
+
+            case 'register-worker': {
+                const targets = message.requestData?.targets || []
+                if (!targets.length) {
+                    connection.send(new ResponseMessage().setError(`targets are empty`))
+                    break
+                }
+
+                workers.add(connection, targets)
+                connection.send(new ResponseMessage().setData('ok'))
+                break
+            }
+
+            case 'poke': {
+                const targets = message.requestData?.targets || []
+                if (!targets.length) {
+                    connection.send(new ResponseMessage().setError(`targets are empty`))
+                    break
+                }
+
+                workers.poke(targets)
+                connection.send(new ResponseMessage().setData('ok'))
+                break
+            }
+
+            case 'status':
+                const info = workers.getInfo()
+                connection.send(new ResponseMessage().setData({
+                    workers: info,
+                    memoryUsage: process.memoryUsage()
+                }))
+                break
+
+            default:
+                connection.send(new ResponseMessage().setError(`unknown request type: '${message.requestType}'`))
+                break
+        }
+    } catch (error) {
+        logger.error(`error while handling message:`, message, error)
+        connection.send(new ResponseMessage().setError('server error: ' + error?.message))
+    }
+}
+
+function usage() {
+    let s = `${process.argv[1]} OPTIONS
+
+Options:
+    --config <path>`
+    console.log(s)
+}
+
+function term() {
+    if (logger)
+        logger.info('shutdown')
+
+    loggerModule.shutdown(function() {
+        process.exit()
+    })
+}
diff --git a/src/jobd.js b/src/jobd.js
new file mode 100755
index 0000000..6567d06
--- /dev/null
+++ b/src/jobd.js
@@ -0,0 +1,244 @@
+#!/usr/bin/env node
+const minimist = require('minimist')
+const loggerModule = require('./logger')
+const configModule = require('./config')
+const db = require('./db')
+const {Server, Connection, RequestMessage, ResponseMessage} = require('./server')
+const {Worker, STATUS_MANUAL} = require('./worker')
+
+const {workerConfig} = configModule
+
+
+/**
+ * @type {Worker}
+ */
+let worker
+
+/**
+ * @type {Logger}
+ */
+let logger
+
+/**
+ * @type {Server}
+ */
+let server
+
+/**
+ * @type {object.<string, Connection>}
+ */
+let jobDoneAwaiters = {}
+
+
+main().catch(e => {
+    console.error(e)
+    process.exit(1)
+})
+
+
+async function main() {
+    if (process.argv.length < 3) {
+        usage()
+        process.exit(0)
+    }
+
+    process.on('SIGINT', term)
+    process.on('SIGTERM', term)
+
+    const argv = minimist(process.argv.slice(2))
+    if (!argv.config)
+        throw new Error('--config option is required')
+
+    // read config
+    try {
+        configModule.parseWorkerConfig(argv.config)
+    } catch (e) {
+        console.error(`config parsing error: ${e.message}`)
+        process.exit(1)
+    }
+
+    await loggerModule.init({
+        file: workerConfig.log_file,
+        levelFile: workerConfig.log_level_file,
+        levelConsole: workerConfig.log_level_console,
+    })
+    logger = loggerModule.getLogger('jobd')
+
+    // console.log(workerConfig)
+
+    // init database
+    try {
+        await db.init()
+    } catch (error) {
+        logger.error('failed to connect to MySQL', error)
+        process.exit(1)
+    }
+    logger.info('db initialized')
+
+    // init queue
+    worker = new Worker()
+    for (let targetName in workerConfig.targets) {
+        let slots = workerConfig.targets[targetName].slots
+        // let target = new Target({name: targetName})
+        // queue.addTarget(target)
+
+        for (let slotName in slots) {
+            let slotLimit = slots[slotName]
+            worker.addSlot(targetName, slotName, slotLimit)
+        }
+    }
+    worker.on('job-done', (data) => {
+        if (jobDoneAwaiters[data.id] !== undefined) {
+            jobDoneAwaiters[data.id].send(new ResponseMessage().setData(data))
+            jobDoneAwaiters[data.id].close()
+            delete jobDoneAwaiters[data.id]
+        }
+    })
+    logger.info('queue initialized')
+
+    // start server
+    server = new Server()
+    server.on('message', onMessage)
+    server.start(workerConfig.port, workerConfig.host)
+    logger.info('server started')
+
+    // connect to master
+    if (workerConfig.master_port && workerConfig.master_host)
+        connectToMaster()
+}
+
+
+/**
+ * @param {RequestMessage|ResponseMessage} message
+ * @param {Connection} connection
+ * @return {Promise<*>}
+ */
+async function onMessage({message, connection}) {
+    try {
+        if (!(message instanceof RequestMessage)) {
+            logger.debug('ignoring message', message)
+            return
+        }
+
+        if (message.requestType !== 'ping')
+            logger.info('onMessage:', message)
+
+        if (workerConfig.password && message.password !== workerConfig.password) {
+            connection.send(new ResponseMessage().setError('invalid password'))
+            return connection.close()
+        }
+
+        switch (message.requestType) {
+            case 'ping':
+                connection.send(new ResponseMessage().setData('pong'))
+                break
+
+            case 'poll':
+                const targets = message.requestData?.targets || []
+                if (!targets.length) {
+                    connection.send(new ResponseMessage().setError('empty targets'))
+                    break
+                }
+
+                for (const t of targets) {
+                    if (!worker.hasTarget(t)) {
+                        connection.send(new ResponseMessage().setError(`invalid target '${t}'`))
+                        break
+                    }
+                }
+
+                worker.setPollTargets(targets)
+                worker.poll()
+
+                connection.send(new ResponseMessage().setData('ok'));
+                break
+
+            case 'status':
+                const qs = worker.getStatus()
+                connection.send(
+                    new ResponseMessage().setData({
+                        queue: qs,
+                        jobDoneAwaitersCount: Object.keys(jobDoneAwaiters).length,
+                        memoryUsage: process.memoryUsage()
+                    })
+                )
+                break
+
+            case 'run-manual':
+                const {id} = message.requestData
+                if (id in jobDoneAwaiters) {
+                    connection.send(new ResponseMessage().setError('another client is already waiting this job'))
+                    break
+                }
+
+                jobDoneAwaiters[id] = connection
+
+                const {accepted} = await worker.getTasks(null, STATUS_MANUAL, {id})
+                if (!accepted) {
+                    delete jobDoneAwaiters[id]
+                    connection.send(new ResponseMessage().setError('failed to run task')) // would be nice to provide some error...
+                }
+
+                break
+
+            default:
+                connection.send(new ResponseMessage().setError(`unknown request type: '${message.requestType}'`))
+                break
+        }
+    } catch (error) {
+        logger.error(`error while handling message:`, message, error)
+        connection.send(new ResponseMessage().setError('server error: ' + error?.message))
+    }
+}
+
+
+function connectToMaster() {
+    const connection = new Connection()
+    connection.connect(workerConfig.master_host, workerConfig.master_port)
+
+    connection.on('connect', function() {
+        connection.send(
+            new RequestMessage('register-worker', {
+                targets: worker.getTargets()
+            })
+        )
+    })
+
+    connection.on('close', () => {
+        logger.warn(`connectToMaster: connection closed`)
+        setTimeout(() => {
+            connectToMaster()
+        }, workerConfig.master_reconnect_timeout * 1000)
+    })
+
+    connection.on('message', (message) => {
+        if (!(message instanceof RequestMessage)) {
+            logger.debug('message from master is not a request, hmm... skipping', message)
+            return
+        }
+
+        onMessage({message, connection})
+            .catch((error) => {
+                logger.error('connectToMaster: onMessage:', error)
+            })
+    })
+}
+
+
+function usage() {
+    let s = `${process.argv[1]} OPTIONS
+
+Options:
+    --config <path>`
+    console.log(s)
+}
+
+
+function term() {
+    if (logger)
+        logger.info('shutdown')
+
+    loggerModule.shutdown(function() {
+        process.exit()
+    })
+}
\ No newline at end of file
diff --git a/src/logger.js b/src/logger.js
new file mode 100644
index 0000000..22dd679
--- /dev/null
+++ b/src/logger.js
@@ -0,0 +1,97 @@
+const log4js = require('log4js')
+const fs = require('fs/promises')
+const fsConstants = require('fs').constants
+const util = require('util')
+
+module.exports = {
+    /**
+     * @param {string} file
+     * @param {string} levelFile
+     * @param {string} levelConsole
+     */
+    async init({file, levelFile, levelConsole}) {
+        const categories = {
+            default: {
+                appenders: ['stdout-filter'],
+                level: 'trace'
+            }
+        }
+
+        const appenders = {
+            stdout: {
+                type: 'stdout',
+                level: 'trace'
+            },
+            'stdout-filter': {
+                type: 'logLevelFilter',
+                appender: 'stdout',
+                level: levelConsole
+            }
+        }
+
+        if (file) {
+            let exists
+            try {
+                await fs.stat(file)
+                exists = true
+            } catch (error) {
+                exists = false
+            }
+
+            // if file exists
+            if (exists) {
+                // see if it's writable
+                try {
+                    // this promise fullfills with undefined upon success
+                    await fs.access(file, fsConstants.W_OK)
+                } catch (error) {
+                    throw new Error(`file '${file}' is not writable:` + error.message)
+                }
+            } else {
+                // try to create an empty file
+                let fd
+                try {
+                    fd = await fs.open(file, 'wx')
+                } catch (error) {
+                    throw new Error(`failed to create file '${file}': ` + error.message)
+                } finally {
+                    await fd?.close()
+                }
+            }
+
+            categories.default.appenders.push('file-filter')
+            appenders.file = {
+                type: 'file',
+                filename: file,
+                maxLogSize: 1024 * 1024 * 50,
+                debug: 'debug'
+            }
+            appenders['file-filter'] = {
+                type: 'logLevelFilter',
+                appender: 'file',
+                level: levelFile
+            }
+        }
+
+        log4js.configure({
+            appenders,
+            categories
+        })
+    },
+
+    /**
+     * @return {Logger}
+     */
+    getLogger(...args) {
+        return log4js.getLogger(...args)
+    },
+
+    /**
+     * @param cb
+     */
+    shutdown(cb) {
+        log4js.shutdown(cb)
+    },
+
+    Logger: log4js.Logger,
+}
diff --git a/src/server.js b/src/server.js
new file mode 100644
index 0000000..b5eca9a
--- /dev/null
+++ b/src/server.js
@@ -0,0 +1,450 @@
+const net = require('net')
+const EventEmitter = require('events')
+const {getLogger} = require('./logger')
+const isObject = require('lodash/isObject')
+
+const EOT = 0x04
+
+class Message {
+
+    static REQUEST = 0
+    static RESPONSE = 1
+
+    /**
+     * @param {number} type
+     */
+    constructor(type) {
+        /**
+         * @type {number}
+         */
+        this.type = type
+    }
+
+    getAsObject() {
+        return [this.type]
+    }
+
+}
+
+class ResponseMessage extends Message {
+    constructor() {
+        super(Message.RESPONSE)
+
+        this.error = null
+        this.data = null
+    }
+
+    setError(error) {
+        this.error = error
+        return this
+    }
+
+    setData(data) {
+        this.data = data
+        return this
+    }
+
+    getAsObject() {
+        return [
+            ...super.getAsObject(),
+            [
+                this.error,
+                this.data
+            ]
+        ]
+    }
+}
+
+class RequestMessage extends Message {
+    /**
+     * @param {string} type
+     * @param {any} data
+     */
+    constructor(type, data = null) {
+        super(Message.REQUEST)
+
+        /**
+         * @type string
+         */
+        this.requestType = type
+
+        /**
+         * @type any
+         */
+        this.requestData = data
+
+        /**
+         * @type {null|string}
+         */
+        this.password = null
+    }
+
+    getAsObject() {
+        let request = {
+            type: this.requestType
+        }
+
+        if (this.requestData)
+            request.data = this.requestData
+
+        return [
+            ...super.getAsObject(),
+            request
+        ]
+    }
+
+    /**
+     * @param {string} password
+     */
+    setPassword(password) {
+        this.password = password
+    }
+}
+
+class Server extends EventEmitter {
+
+    constructor() {
+        super()
+
+        /**
+         * @type {null|module:net.Server}
+         */
+        this.server = null
+
+        /**
+         * @type {Logger}
+         */
+        this.logger = getLogger('server')
+    }
+
+    /**
+     * @param {number} port
+     * @param {string} host
+     */
+    start(port, host) {
+        this.server = net.createServer()
+
+        this.server.on('connection', this.onConnection)
+        this.server.on('error', this.onError)
+        this.server.on('listening', this.onListening)
+
+        this.server.listen(port, host)
+    }
+
+    /**
+     * @param {module:net.Socket} socket
+     */
+    onConnection = (socket) => {
+        let connection = new Connection()
+        connection.setSocket(socket)
+        connection.on('message', (message) => {
+            this.emit('message', {
+                message,
+                connection
+            })
+        })
+
+        this.logger.info(`new connection from ${socket.remoteAddress}:${socket.remotePort}`)
+    }
+
+    onListening = () => {
+        let addr = this.server.address()
+        this.logger.info(`server is listening on ${addr.address}:${addr.port}`)
+    }
+
+    onError = (error) => {
+        this.logger.error('error: ', error)
+    }
+
+}
+
+class Connection extends EventEmitter {
+
+    constructor() {
+        super()
+
+        /**
+         * @type {null|module:net.Socket}
+         */
+        this.socket = null
+
+        /**
+         * @type {Buffer}
+         */
+        this.data = Buffer.from([])
+
+        /**
+         * @type {boolean}
+         * @private
+         */
+        this._closeEmitted = false
+
+        /**
+         * @type {null|string}
+         */
+        this.remoteAddress = null
+
+        /**
+         * @type {null|number}
+         */
+        this.remotePort = null
+
+        /**
+         * @type {null|number}
+         */
+        this.id = null
+
+        this._setLogger()
+    }
+
+    /**
+     * @param {string} host
+     * @param {number} port
+     */
+    connect(host, port) {
+        if (this.socket !== null)
+            throw new Error(`this Connection already has a socket`)
+
+        this.socket = new net.Socket()
+        this.socket.connect({host, port})
+
+        this.remoteAddress = host
+        this.remotePort = port
+
+        this._setId()
+        this._setLogger()
+        this._setSocketEvents()
+    }
+
+    /**
+     * @param {module:net.Socket} socket
+     */
+    setSocket(socket) {
+        this.socket = socket
+
+        this.remoteAddress = socket.remoteAddress
+        this.remotePort = socket.remotePort
+
+        this._setId()
+        this._setLogger()
+        this._setSocketEvents()
+    }
+
+    /**
+     * @private
+     */
+    _setLogger() {
+        let addr = this.socket ? this.remoteAddr() : '?'
+        this.logger = getLogger(`<Connection ${this.id} ${addr}>`)
+    }
+
+    /**
+     * @private
+     */
+    _setId() {
+        this.id = Math.floor(Math.random() * 10000)
+    }
+
+    /**
+     * @private
+     */
+    _setSocketEvents() {
+        this.socket.on('connect', this.onConnect)
+        this.socket.on('data', this.onData)
+        this.socket.on('end', this.onEnd)
+        this.socket.on('close', this.onClose)
+        this.socket.on('error', this.onError)
+    }
+
+    /**
+     * @param {Buffer} data
+     * @private
+     */
+    _appendToBuffer(data) {
+        this.data = Buffer.concat([this.data, data])
+    }
+
+    /**
+     * @return {string}
+     */
+    remoteAddr() {
+        return this.remoteAddress + ':' + this.remotePort
+    }
+
+    /**
+     * @private
+     */
+    _processChunks() {
+        if (!this.data.length)
+            return
+
+        this.logger.trace(`processChunks (start):`, this.data)
+
+        /**
+         * @type {Buffer[]}
+         */
+        let messages = []
+        let offset = 0
+        let eotPos
+        do {
+            eotPos = this.data.indexOf(EOT, offset)
+            if (eotPos !== -1) {
+                let message = this.data.slice(offset, eotPos)
+                messages.push(message)
+
+                this.logger.debug(`processChunks: found new message (${offset}, ${eotPos})`)
+                offset = eotPos + 1
+            }
+        } while (eotPos !== -1 && offset < this.data.length-1)
+
+        if (offset !== 0) {
+            this.data = this.data.slice(offset)
+            this.logger.trace(`processChunks: slicing data from ${offset}`)
+        }
+
+        this.logger.trace(`processChunks (after parsing):`, this.data)
+
+        for (let message of messages) {
+            try {
+                let buf = message.toString('utf-8')
+                this.logger.debug(buf)
+
+                let json = JSON.parse(buf)
+                this._emitMessage(json)
+            } catch (error) {
+                this.logger.error('failed to parse data as JSON')
+                this.logger.debug(message)
+            }
+        }
+    }
+
+    /**
+     * @param {object} json
+     * @private
+     */
+    _emitMessage(json) {
+        if (!Array.isArray(json)) {
+            this.logger.error('malformed message, JSON array expected', json)
+            return
+        }
+
+        let type = json.shift()
+        let message
+        switch (type) {
+            case Message.REQUEST: {
+                let data = json.shift()
+                if (!data || !isObject(data)) {
+                    this.logger.error('malformed REQUEST message')
+                    return
+                }
+
+                message = new RequestMessage(data.type, data.data || null)
+                if (data.password)
+                    message.setPassword(data.password)
+                break
+            }
+
+            case Message.RESPONSE: {
+                let data = json.shift()
+                if (!data || !Array.isArray(data) || data.length < 2) {
+                    this.logger.error('malformed RESPONSE message')
+                    return
+                }
+
+                message = new ResponseMessage()
+                message.setError(data[0]).setData(data[1])
+
+                break
+            }
+
+            default:
+                this.logger.error(`malformed message, unexpected type ${type}`)
+                return
+        }
+
+        this.emit('message', message)
+    }
+
+    /**
+     * @type {Message} data
+     * @param message
+     */
+    send(message) {
+        if (!(message instanceof Message))
+            throw new Error('send expects Message, got', message)
+
+        let json = JSON.stringify(message.getAsObject())
+        let buf = Buffer.concat([
+            Buffer.from(json),
+            Buffer.from([EOT])
+        ])
+
+        this.logger.debug('send:', json)
+        this.logger.trace('send:', buf)
+
+        try {
+            this.socket.write(buf)
+        } catch (error) {
+            this.logger.error(`processChunks: failed to write response ${JSON.stringify(message)} to a socket`, error)
+        }
+    }
+
+    /**
+     */
+    close() {
+        try {
+            this.socket.end()
+            this.socket.destroy()
+            this._emitClose()
+        } catch (error) {
+            this.logger.error('close:', error)
+        }
+    }
+
+    /**
+     * @private
+     */
+    _emitClose() {
+        if (this._closeEmitted)
+            return
+
+        this._closeEmitted = true
+        this.emit('close')
+    }
+
+    onConnect = () => {
+        this.logger.debug('connection established')
+        this.emit('connect')
+    }
+
+    onData = (data) => {
+        this.logger.trace('onData', data)
+        this._appendToBuffer(data)
+        this._processChunks()
+    }
+
+    onEnd = (data) => {
+        if (data)
+            this._appendToBuffer(data)
+
+        this._processChunks()
+    }
+
+    onClose = (hadError) => {
+        this._emitClose()
+        this.logger.debug(`socket closed` + (hadError ? ` with error` : ''))
+    }
+
+    onError = (error) => {
+        this._emitClose()
+        this.logger.warn(`socket error:`, error)
+    }
+    
+}
+
+module.exports = {
+    Server,
+    Connection,
+    RequestMessage,
+    ResponseMessage
+}
\ No newline at end of file
diff --git a/src/util.js b/src/util.js
new file mode 100644
index 0000000..6de07e5
--- /dev/null
+++ b/src/util.js
@@ -0,0 +1,9 @@
+module.exports = {
+    timestamp() {
+        return parseInt(+(new Date())/1000)
+    },
+
+    isNumeric(n) {
+        return !isNaN(parseFloat(n)) && isFinite(n)
+    }
+}
\ No newline at end of file
diff --git a/src/worker.js b/src/worker.js
new file mode 100644
index 0000000..3151b40
--- /dev/null
+++ b/src/worker.js
@@ -0,0 +1,472 @@
+const Queue = require('queue')
+const child_process = require('child_process')
+const db = require('./db')
+const {timestamp} = require('./util')
+const {getLogger} = require('./logger')
+const EventEmitter = require('events')
+const {workerConfig} = require('./config')
+
+const STATUS_WAITING = 'waiting'
+const STATUS_MANUAL = 'manual'
+const STATUS_ACCEPTED = 'accepted'
+const STATUS_IGNORED = 'ignored'
+const STATUS_RUNNING = 'running'
+const STATUS_DONE = 'done'
+
+const RESULT_OK = 'ok'
+const RESULT_FAIL = 'fail'
+
+class Worker extends EventEmitter {
+
+    constructor() {
+        super()
+
+        /**
+         * @type {object.<string, {slots: object.<string, {limit: number, queue: Queue}>}>}
+         */
+        this.targets = {}
+
+        /**
+         * @type {boolean}
+         */
+        this.polling = false
+
+        /**
+         * @type {boolean}
+         */
+        this.nextpoll = {}
+
+        /**
+         * @type {Logger}
+         */
+        this.logger = getLogger('Worker')
+    }
+
+    /**
+     * @param {string} target
+     * @param {string} slot
+     * @param {number} limit
+     */
+    addSlot(target, slot, limit) {
+        this.logger.debug(`addSlot: adding slot '${slot}' for target' ${target}' (limit: ${limit})`)
+
+        if (this.targets[target] === undefined)
+            this.targets[target] = {slots: {}}
+
+        if (this.targets[target].slots[slot] !== undefined)
+            throw new Error(`slot ${slot} for target ${target} has already been added`)
+
+        let queue = Queue({
+            concurrency: limit,
+            autostart: true
+        })
+        queue.on('success', this.onJobFinished.bind(this, target, slot))
+        queue.on('error', this.onJobFinished.bind(this, target, slot))
+        queue.start()
+
+        this.targets[target].slots[slot] = {limit, queue}
+    }
+
+    /**
+     * @param {string} target
+     * @returns {boolean}
+     */
+    hasTarget(target) {
+        return (target in this.targets)
+    }
+
+    /**
+     * Returns status of all queues.
+     *
+     * @return {object}
+     */
+    getStatus() {
+        let status = {targets: {}}
+        for (const targetName in this.targets) {
+            let target = this.targets[targetName]
+            status.targets[targetName] = {}
+            for (const slotName in target.slots) {
+                const {queue, limit} = target.slots[slotName]
+                status.targets[targetName][slotName] = {
+                    concurrency: queue.concurrency,
+                    limit,
+                    length: queue.length,
+                }
+            }
+        }
+        return status
+    }
+
+    /**
+     * @return {string[]}
+     */
+    getTargets() {
+        return Object.keys(this.targets)
+    }
+
+    /**
+     *
+     */
+    poll() {
+        const LOGPREFIX = `poll():`
+
+        let targets = this.getPollTargets()
+        if (!targets.length) {
+            this.poller.warn(`${LOGPREFIX} no targets`)
+            return
+        }
+
+        // skip and postpone the poll, if we're in the middle on another poll
+        // it will be called again from the last .then() at the end of this method
+        if (this.polling) {
+            this.logger.debug(`${LOGPREFIX} already polling`)
+            return
+        }
+
+        // skip and postpone the poll, if no free slots
+        // it will be called again from onJobFinished()
+        if (!this.hasFreeSlots(targets)) {
+            this.logger.debug(`${LOGPREFIX} no free slots`)
+            return
+        }
+
+        // set polling flag
+        this.polling = true
+
+        // clear postponed polls target list
+        this.setPollTargets()
+
+        this.logger.debug(`${LOGPREFIX} calling getTasks(${JSON.stringify(targets)})`)
+        this.getTasks(targets)
+            .then(({rows}) => {
+                let message = `${LOGPREFIX} ${rows} processed`
+                if (workerConfig.mysql_fetch_limit && rows >= workerConfig.mysql_fetch_limit) {
+                    // it seems, there are more, so we'll need to perform another query
+                    this.setPollTargets(targets)
+                    message += `, scheduling more polls (targets: ${JSON.stringify(this.getPollTargets())})`
+                }
+                this.logger.debug(message)
+            })
+            .catch((error) => {
+                this.logger.error(`${LOGPREFIX}`, error)
+                //this.setPollTargets(targets)
+            })
+            .then(() => {
+                // unset polling flag
+                this.polling = false
+
+                // perform another poll, if needed
+                if (this.getPollTargets().length > 0) {
+                    this.logger.debug(`${LOGPREFIX} next poll scheduled, calling poll() again`)
+                    this.poll()
+                }
+            })
+    }
+
+    /**
+     * @param {string|string[]|null} target
+     */
+    setPollTargets(target) {
+        // when called without parameter, remove all targets
+        if (target === undefined) {
+            this.nextpoll = {}
+            return
+        }
+
+        // just a fix
+        if (target === 'null')
+            target = null
+
+        if (Array.isArray(target)) {
+            target.forEach(t => {
+                this.nextpoll[t] = true
+            })
+        } else {
+            if (target === null)
+                this.nextpoll = {}
+            this.nextpoll[target] = true
+        }
+    }
+
+    /**
+     * @return {string[]}
+     */
+    getPollTargets() {
+        if (null in this.nextpoll)
+            return Object.keys(this.targets)
+
+        return Object.keys(this.nextpoll)
+    }
+
+    /**
+     * @param {string} target
+     * @return {boolean}
+     */
+    hasPollTarget(target) {
+        return target in this.nextpoll || null in this.nextpoll
+    }
+
+    /**
+     * @param {string|null|string[]} target
+     * @param {string} reqstatus
+     * @param {object} data
+     * @returns {Promise<{ignored: number, accepted: number, rows: number}>}
+     */
+    async getTasks(target = null, reqstatus = STATUS_WAITING, data = {}) {
+        const LOGPREFIX = `getTasks(${JSON.stringify(target)}, '${reqstatus}', ${JSON.stringify(data)}):`
+        
+        // get new jobs in transaction
+        await db.beginTransaction()
+
+        let sqlFields = `id, status, target, slot`
+        let sql
+        if (data.id) {
+            sql = `SELECT ${sqlFields} FROM ${workerConfig.mysql_table} WHERE id=${db.escape(data.id)} FOR UPDATE`
+        } else {
+            let targets
+            if (target === null) {
+                targets = Object.keys(this.targets)
+            } else if (!Array.isArray(target)) {
+                targets = [target]
+            }  else {
+                targets = target
+            }
+            let sqlLimit = workerConfig.mysql_fetch_limit !== 0 ? ` LIMIT 0, ${workerConfig.mysql_fetch_limit}` : ''
+            let sqlWhere = `status=${db.escape(reqstatus)} AND target IN (`+targets.map(db.escape).join(',')+`)`
+            sql = `SELECT ${sqlFields} FROM ${workerConfig.mysql_table} WHERE ${sqlWhere} ORDER BY id ${sqlLimit} FOR UPDATE`
+        }
+
+        /** @type {object[]} results */
+        let results = await db.query(sql)
+        this.logger.trace(`${LOGPREFIX} query result:`, results)
+
+        /**
+         * @type {{target: string, slot: string, id: number}[]}
+         */
+        let accepted = []
+
+        /**
+         * @type {number[]}
+         */
+        let ignored = []
+
+        for (let result of results) {
+            let {id, slot, target, status} = result
+            id = parseInt(id)
+
+            if (status !== reqstatus) {
+                this.logger.warn(`${LOGPREFIX} status = ${status} != ${reqstatus}`)
+                ignored.push(id)
+                continue
+            }
+
+            if (!target || this.targets[target] === undefined) {
+                this.logger.error(`${LOGPREFIX} target '${target}' not found (job id=${id})`)
+                ignored.push(id)
+                continue
+            }
+
+            if (!slot || this.targets[target].slots[slot] === undefined) {
+                this.logger.error(`${LOGPREFIX} slot '${slot}' of target '${target}' not found (job id=${id})`)
+                ignored.push(id)
+                continue
+            }
+
+            this.logger.debug(`${LOGPREFIX} accepted target='${target}', slot='${slot}', id=${id}`)
+            accepted.push({target, slot, id})
+        }
+
+        if (accepted.length)
+            await db.query(`UPDATE ${workerConfig.mysql_table} SET status='accepted' WHERE id IN (`+accepted.map(j => j.id).join(',')+`)`)
+
+        if (ignored.length)
+            await db.query(`UPDATE ${workerConfig.mysql_table} SET status='ignored' WHERE id IN (`+ignored.join(',')+`)`)
+
+        await db.commit()
+
+        accepted.forEach(({id, target, slot}) => {
+            let q = this.targets[target].slots[slot].queue
+            q.push(async (cb) => {
+                let data = {
+                    code: null,
+                    signal: null,
+                    stdout: '',
+                    stderr: ''
+                }
+                let result = RESULT_OK
+
+                try {
+                    await this.setJobStatus(id, STATUS_RUNNING)
+
+                    Object.assign(data, (await this.run(id)))
+                    if (data.code !== 0)
+                        result = RESULT_FAIL
+                } catch (error) {
+                    this.logger.error(`${LOGPREFIX} job ${id}: error while run():`, error)
+                    result = RESULT_FAIL
+                    data.stderr = (error instanceof Error) ? (error.message + '\n' + error.stack) : (error + '')
+                } finally {
+                    this.emit('job-done', {
+                        id,
+                        result,
+                        ...data
+                    })
+
+                    try {
+                        await this.setJobStatus(id, STATUS_DONE, result, data)
+                    } catch (error) {
+                        this.logger.error(`${LOGPREFIX} setJobStatus(${id})`, error)
+                    }
+                    
+                    cb()
+                }
+            })
+        })
+
+        return {
+            rows: results.length,
+            accepted: accepted.length,
+            ignored: ignored.length,
+        }
+    }
+
+    /**
+     * @param {number} id
+     */
+    async run(id) {
+        let command = workerConfig.launcher.replace(/\{id\}/g, id)
+        let args = command.split(/ +/)
+        return new Promise((resolve, reject) => {
+            this.logger.info(`run(${id}): launching`, args)
+
+            let process = child_process.spawn(args[0], args.slice(1), {
+                maxBuffer: workerConfig.max_output_buffer
+            })
+            
+            let stdoutChunks = []
+            let stderrChunks = []
+
+            process.on('exit',
+                /**
+                 * @param {null|number} code
+                 * @param {null|string} signal
+                 */
+                (code, signal) => {
+                    let stdout = stdoutChunks.join('')
+                    let stderr = stderrChunks.join('')
+
+                    stdoutChunks = undefined
+                    stderrChunks = undefined
+
+                    resolve({
+                        code,
+                        signal,
+                        stdout,
+                        stderr
+                    })
+                })
+
+            process.on('error', (error) => {
+                reject(error)
+            })
+
+            process.stdout.on('data', (data) => {
+                if (data instanceof Buffer)
+                    data = data.toString('utf-8')
+                stdoutChunks.push(data)
+            })
+
+            process.stderr.on('data', (data) => {
+                if (data instanceof Buffer)
+                    data = data.toString('utf-8')
+                stderrChunks.push(data)
+            })
+        })
+    }
+
+    /**
+     * @param {number} id
+     * @param {string} status
+     * @param {string} result
+     * @param {object} data
+     * @return {Promise<void>}
+     */
+    async setJobStatus(id, status, result = RESULT_OK, data = {}) {
+        let update = {
+            status,
+            result
+        }
+        switch (status) {
+            case STATUS_RUNNING:
+            case STATUS_DONE:
+                update[status === STATUS_RUNNING ? 'time_started' : 'time_finished'] = timestamp()
+                break
+        }
+        if (data.code !== undefined)
+            update.return_code = data.code
+        if (data.signal !== undefined)
+            update.sig = data.signal
+        if (data.stderr !== undefined)
+            update.stderr = data.stderr
+        if (data.stdout !== undefined)
+            update.stdout = data.stdout
+
+        let list = []
+        for (let field in update) {
+            let val = update[field]
+            if (val !== null)
+                val = db.escape(val)
+            list.push(`${field}=${val}`)
+        }
+
+        await db.query(`UPDATE ${workerConfig.mysql_table} SET ${list.join(', ')} WHERE id=?`, [id])
+    }
+
+    /**
+     * @param {string[]} inTargets
+     * @returns {boolean}
+     */
+    hasFreeSlots(inTargets = []) {
+        const LOGPREFIX = `hasFreeSlots(${JSON.stringify(inTargets)}):`
+
+        this.logger.debug(`${LOGPREFIX} entered`)
+
+        for (const target in this.targets) {
+            if (!inTargets.includes(target))
+                continue
+
+            for (const slot in this.targets[target].slots) {
+                const {limit, queue} = this.targets[target].slots[slot]
+                this.logger.debug(LOGPREFIX, limit, queue.length)
+                if (queue.length < limit)
+                    return true
+            }
+        }
+
+        return false
+    }
+
+    /**
+     * @param {string} target
+     * @param {string} slot
+     */
+    onJobFinished = (target, slot) => {
+        this.logger.debug(`onJobFinished: target=${target}, slot=${slot}`)
+        const {queue, limit} = this.targets[target].slots[slot]
+        if (queue.length < limit && this.hasPollTarget(target)) {
+            this.logger.debug(`onJobFinished: ${queue.length} < ${limit}, calling poll(${target})`)
+            this.poll()
+        }
+    }
+
+}
+
+module.exports = {
+    Worker,
+    STATUS_WAITING,
+    STATUS_MANUAL,
+    STATUS_ACCEPTED,
+    STATUS_IGNORED,
+    STATUS_RUNNING,
+    STATUS_DONE,
+}
\ No newline at end of file
diff --git a/src/workers-list.js b/src/workers-list.js
new file mode 100644
index 0000000..96a127a
--- /dev/null
+++ b/src/workers-list.js
@@ -0,0 +1,145 @@
+const intersection = require('lodash/intersection')
+const {masterConfig} = require('./config')
+const {getLogger} = require('./logger')
+const {RequestMessage} = require('./server')
+const throttle = require('lodash/throttle')
+
+class WorkersList {
+
+    constructor() {
+        /**
+         * @type {{connection: Connection, targets: string[]}[]}
+         */
+        this.workers = []
+
+        /**
+         * @type {object.<string, boolean>}
+         */
+        this.targetsToPoke = {}
+
+        /**
+         * @type {object.<string, boolean>}
+         */
+        this.targetsWaitingToPoke = {}
+
+        /**
+         * @type {NodeJS.Timeout}
+         */
+        this.pingInterval = setInterval(this.sendPings, masterConfig.ping_interval * 1000)
+
+        /**
+         * @type {Logger}
+         */
+        this.logger = getLogger('WorkersList')
+    }
+
+    /**
+     * @param {Connection} connection
+     * @param {string[]} targets
+     */
+    add(connection, targets) {
+        this.logger.info(`add: connection from ${connection.remoteAddr()}, targets ${JSON.stringify(targets)}`)
+
+        this.workers.push({connection, targets})
+        connection.on('close', () => {
+            this.logger.info(`connection from ${connection.remoteAddr()} closed, removing worker`)
+            this.workers = this.workers.filter(worker => {
+                return worker.connection !== connection
+            })
+        })
+
+        let waiting = Object.keys(this.targetsWaitingToPoke)
+        if (!waiting.length)
+            return
+
+        let intrs = intersection(waiting, targets)
+        if (intrs.length) {
+            this.logger.info('add: found intersection with waiting targets:', intrs, 'going to poke new worker')
+            this._pokeWorkerConnection(connection, intrs)
+            for (let target of intrs)
+                delete this.targetsWaitingToPoke[target]
+            this.logger.trace(`add: this.targetsWaitingToPoke:`, this.targetsWaitingToPoke)
+        }
+    }
+
+    /**
+     * @param {string[]} targets
+     */
+    poke(targets) {
+        this.logger.debug('poke:', targets)
+        if (!Array.isArray(targets))
+            throw new Error('targets must be Array')
+
+        for (let t of targets)
+            this.targetsToPoke[t] = true
+
+        this._pokeWorkers()
+    }
+
+    /**
+     * @private
+     */
+    _pokeWorkers = throttle(() => {
+        const targets = Object.keys(this.targetsToPoke)
+        this.targetsToPoke = {}
+
+        const found = {}
+        for (const worker of this.workers) {
+            const intrs = intersection(worker.targets, targets)
+            intrs.forEach(t => {
+                found[t] = true
+            })
+            if (intrs.length > 0)
+                this._pokeWorkerConnection(worker.connection, targets)
+        }
+
+        for (let target of targets) {
+            if (!(target in found)) {
+                this.logger.debug(`_pokeWorkers: worker responsible for ${target} not found. we'll remember it`)
+                this.targetsWaitingToPoke[target] = true
+            }
+            this.logger.trace('_pokeWorkers: this.targetsWaitingToPoke:', this.targetsWaitingToPoke)
+        }
+    }, masterConfig.poke_throttle_interval * 1000, {leading: true})
+
+    /**
+     * @param {Connection} connection
+     * @param {string[]} targets
+     * @private
+     */
+    _pokeWorkerConnection(connection, targets) {
+        this.logger.debug('_pokeWorkerConnection:', connection.remoteAddr(), targets)
+        connection.send(
+            new RequestMessage('poll', {
+                targets
+            })
+        )
+    }
+
+    /**
+     * @return {{targets: string[], remoteAddr: string, remotePort: number}[]}
+     */
+    getInfo() {
+        return this.workers.map(worker => {
+            return {
+                remoteAddr: worker.connection.socket?.remoteAddress,
+                remotePort: worker.connection.socket?.remotePort,
+                targets: worker.targets
+            }
+        })
+    }
+
+    /**
+     * @private
+     */
+    sendPings = () => {
+        this.workers
+            .forEach(w => {
+                this.logger.trace(`sending ping to ${w.connection.remoteAddr()}`)
+                w.connection.send(new RequestMessage('ping'))
+            })
+    }
+
+}
+
+module.exports = WorkersList
\ No newline at end of file