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I have an Elastic Beanstalk application which was initially configured to use a Classic Load Balancer. I found that this caused errors when connecting via WebSocket. Because of this, I configured the application to use an Application Load Balancer instead, because I was told that ALBs support WebSockets. However, it seems that they do not: I get exactly the same error when attempting to connect to my ALB via WebSocket.

Do ALBs actually support WebSocket? The AWS documentation is contradictory on this. This page says it only supports HTTP and HTTPS. There are no guides to setting up an ALB to support WebSocket.

I am using Node/Hapi/Socket.io for my server (running on instance derived from Amazon Linux AMI). Basic setup is:

const hapi = require('hapi');
const websocket = require('./WebSocket');
var server = new hapi.Server();
server.connection(config.Application);
websocket.Initialize(server.listener);
where WebSocket.js is
var io = null;
module.exports = {
    Initialize: function (http) {
        io = require('socket.io')(http);
        io.on('connection', function (socket) {
            console.log('Websocket ' + socket.id + ' connected.');
            socket.on('disconnect', function () {
                console.log('Websocket ' + socket.id + ' disconnected.');
I am using Angular 1.5x for my client, with socket.io-client.  It is important to configure the WebSocket client options as follows, or you will not be able to connect.
(function () {
    'use strict';
    angular
        .module('XXXXX', [])
        .run(runHandler);
    runHandler.$inject = ['WebSocketService'];
    function runHandler(WebSocketService) {
       WebSocketService.Initialize();
})();
The WebSocket service:
(function () {
    'use strict';
    angular
        .module('XXXXX')
        .factory('WebSocketService', WebSocketService);
    WebSocketService.$inject = [];
    function WebSocketService() {
        var socket = null;
        function initialize() {
            var url = 'http://' + ALB_URL + ':5800';
            socket = io(url, {transports: ['websocket'], upgrade: false});
            socket.on('connect', function () {
                console.log('Socket connected');
            socket.on('disconnect', function () {
                console.log('Socket disconnected');
        return {
            Initialize: initialize
})();
                What is your health check config? Does socket.io or your application code have a special health check endpoint? In my case, requesting / results in an HTTP 426 response, which ALB doesn't consider healthy.
– dskrvk
                Nov 24, 2016 at 20:20
                I have two VMs behind the ALB.  Each hosts a Node web service.  I have a REST endpoint at http:<server>:5800/v1/monitor/ping that returns the current server date/time as a string with HTTP 200 OK.  I configure this information in my API (non web socket) Target Group->Health Checks.
– programmerj
                Nov 28, 2016 at 17:38
                @programmerj So what would your ALB_URL be? "xxx.us-east-1.elasticbeanstalk.com/socket.io:5800"? Is it required the path be exactly "socket.io" or is it arbitrary? Flask-socketio exposes websocket via port 5000, so would I use port 5000?
– Alpenglow
                Apr 11, 2017 at 15:24
                Hello @Alpenglow.   Going from memory because I no longer use this stack, but the ALB_URL will be the generated URL of the application load balancer, or in my case, a URL created in Route53 that points to the application load balancer.  I don't think the path has to be 'socket.io', as long as the client matches.  I believe you would use 5000 in your case.
– programmerj
                Apr 12, 2017 at 17:22
                Thanks for this post. However has anyone had the problem where the socket disconnects and then it retries? It seems that it stays connected for awhile then looses the connection intermittently. And I noticed it gives "Error during WebSocket handshake: Unexpected response code: 502" - any ideas?
– Aaron
                Dec 26, 2017 at 15:15
Application load balancer supports websocket. But No support for websocket health check till 23 Feb 2017. They may add an option later. You need to set up a HTTP or HTTPS health check for your target group when you want to use a websocket behind Application Load Balancer.
From AWS document:
"Note that health checks do not support WebSockets."  
Reference: http://docs.aws.amazon.com/elasticloadbalancing/latest/application/target-group-health-checks.html
                Just a heads up, we're in 2018, near 2019, and AWS still does not support WSS Health Checks :'( docs.aws.amazon.com/elasticloadbalancing/latest/application/… still sayd
– Cyril Duchon-Doris
                Oct 2, 2018 at 23:37
                Just a heads up, we're in 2022, and AWS still does not support WebSocket Health Checks :'( docs.aws.amazon.com/elasticloadbalancing/latest/application/…
– jenovachild
                May 26, 2022 at 1:41
ALB (Application load balancer) supports websockets. you can check here
also ALB close the connection depending upon idle time out configured.
SnapShot from the above blog
                @coolboyjules why not? It is a link to a blog announcement ALB in which it explicitly mentions it supports websockets, giving a direct answer to the OP question.
– J. Doe
                Dec 8, 2022 at 14:58
In terms of nodejs 
When we use socket io on the client-side and call socket.js library

like this 
const socket = io('domain.com');
what I observed is when I specified Http as protocol then it redirected the call to ws://domain.com but when I specified https then it redirected to wss://domain.com and I was getting this error failed: Error during WebSocket handshake: Unexpected response code: 400
what I did is I specified 
const socket = io(window.location.origin, {reconnect: true,transports: ['websocket']});
which indeed solved my problem
        
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