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Node.js load balancer with
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| /* | |
| * Author: Zaggen | |
| * github: https://github.com/Zaggen | |
| * Free to use and modify | |
| * */ | |
| const httpProxy = require('http-proxy') | |
| const http = require('http') | |
| const proxy = httpProxy.createProxyServer({}) | |
| const Promise = require('bluebird') | |
| // REDIS | |
| const redis = require('redis') | |
| const redisConfig = require('./config/local.js').redisConfig | |
| const redisClient = redis.createClient(redisConfig) | |
| const port = 1337 // Same as the one configured on nginx | |
| Promise.promisifyAll(redis.RedisClient.prototype) | |
| // Queue system vars/consts | |
| const MAX_ATTEMPS = 5 | |
| const REGISTRY_CHECK_TIME = 60000 | |
| const MAX_QUEUE_SIZE = 20 | |
| const queue = [] | |
| let serverIndex = 0 | |
| let serversList | |
| (async function init() { | |
| serversList = await redisClient.lrangeAsync('server-registry', 0, 100) | |
| await validateRegistryAsync(serversList) | |
| let lastRegistryCheck = (new Date()).getTime() | |
| const server = http.createServer(async function(req, res) { | |
| handleRequest(req, res, MAX_ATTEMPS) | |
| }) | |
| async function handleRequest(req, res, retryAttemptsLeft) { | |
| req.retryAttemptsLeft = retryAttemptsLeft | |
| serversList = await redisClient.lrangeAsync('server-registry', 0, 100) | |
| // If 60s has passed since the last request, we validate our registry | |
| if(((new Date()).getTime() - lastRegistryCheck) > REGISTRY_CHECK_TIME){ | |
| serversList = validateRegistryAsync(serversList) | |
| lastRegistryCheck = (new Date()).getTime() | |
| } | |
| // If we have some servers, we process the request | |
| if(serversList.length > 0){ | |
| serverIndex = (serverIndex + 1) % serversList.length | |
| const target = serversList[serverIndex] | |
| // console.log('balancing request to: ', target); | |
| proxy.web(req, res, {target}) | |
| } | |
| else { | |
| queueRequest(req, res) | |
| } | |
| } | |
| function queueRequest(req, res) { | |
| const {retryAttemptsLeft} = req | |
| if(retryAttemptsLeft > 0){ | |
| if(queue.length >= MAX_QUEUE_SIZE) { | |
| const oldestRequest = queue.shift() | |
| sendBadGateWay(oldestRequest.res) | |
| } | |
| queue.push({req, res, retryAttemptsLeft: retryAttemptsLeft - 1}) | |
| const delayMultiplier = (MAX_ATTEMPS + 1) - retryAttemptsLeft | |
| scheduleRetry(queue, delayMultiplier) | |
| } | |
| else { | |
| sendBadGateWay(res) | |
| } | |
| } | |
| function sendBadGateWay(res) { | |
| res.statusCode = 502 | |
| res.statusMessage = 'Bad Gateway' | |
| res.end(` | |
| <body style="text-align: center; padding: 10px;"> | |
| <h1>502 Server Error</h1> | |
| <hr/> | |
| <p> | |
| The server encountered a temporary error and could not complete your request. | |
| Please try again later and if the problem persists then contact support and explain in detail how and when | |
| the error occurred. | |
| </p> | |
| <p>Thank you for your kind understanding.</p> | |
| </body> | |
| `) | |
| } | |
| server.on('upgrade', async function(req, socket, head) { | |
| // console.log('socket connection') | |
| serversList = await redisClient.lrangeAsync('server-registry', 0, 100) | |
| if(serversList.length > 0){ | |
| serverIndex = (serverIndex + 1) % serversList.length | |
| const target = serversList[serverIndex] | |
| // console.log('balancing request to: ', target); | |
| proxy.ws(req, socket, head, {target}); | |
| } | |
| }) | |
| proxy.on('error', function (err, req, res) { | |
| // This will force a registry check on the next request | |
| lastRegistryCheck -= REGISTRY_CHECK_TIME | |
| if(err.code === 'ECONNREFUSED' && req.retryAttemptsLeft > 0){ | |
| queueRequest(req, res) | |
| } | |
| else | |
| sendBadGateWay(res) | |
| }) | |
| function scheduleRetry(queue, delayMultiplier) { | |
| setTimeout(function() { | |
| if(queue.length > 0){ | |
| const {req, res, retryAttemptsLeft} = queue.shift() | |
| if(!res.socket.destroyed){ | |
| // console.log('retryAttemptsLeft', retryAttemptsLeft) | |
| handleRequest(req, res, retryAttemptsLeft) | |
| } | |
| else { | |
| // CONNECTION RESET BY CLIENT | |
| res.end() | |
| } | |
| } | |
| }, 200 * delayMultiplier) | |
| } | |
| async function validateRegistryAsync(serversList) { | |
| const updatedServerList = [] | |
| for (let server of serversList) { | |
| console.log('iterating') | |
| const isAlive = await testEndPoint(server) | |
| if(!isAlive) | |
| redisClient.lremAsync('server-registry', 0, server) | |
| else | |
| updatedServerList.push(server) | |
| } | |
| return updatedServerList | |
| } | |
| async function testEndPoint(url) { | |
| return new Promise((resolve)=> { | |
| try { | |
| http.get(url, ()=> { | |
| resolve(true) | |
| }).on('error', (e) => { | |
| resolve(false) | |
| }); | |
| } catch(err){ | |
| resolve(false) | |
| } | |
| }) | |
| } | |
| server.listen(port, ()=> { | |
| console.log(`Load balancer listening on port ${port}`) | |
| }) | |
| })() |
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redisClient.rpush.apply(redisClient, ['server-registry', serverUrl])(Make sure is not already there or use a set instead)redisClient.lrem('server-registry', 0, serverUrl)