Suddenly my client will not get a connection from server.

I have an app (client && server on separate HEROKU servers)… Its been working perfectly for years. Now all the sudden the connection is intermittent. in v4 the error is 400 in v2 the error is cors… Ive tried almost every cors configuration i can think of.

It looks like the client connect and disconnects several times. sometimes the connection sticks but most of the time it disconnects before the frontend can join a room

It works perfectly with almost any configuration on localhost at all times

Client ==> “socket.io-client”: “^4.4.1”,

this.socket = io(environment.backend, {
      withCredentials: true,
      extraHeaders: { dash: "abcd" },
    });

Server ==> “socket.io”: “^4.4.1”,

this.io = new Server(server, {cors: { 
          origin: env.frontend_url, 
          allowedHeaders: ["dash"],
          credentials: true
        }});

often after a confirmed connection there is the following error

websocket.js:54 WebSocket connection to ‘wss://fornida-api.herokuapp.com/socket.io/?EIO=4&transport=websocket&sid=j64x9KB6m87VHUM4AAAJ’ failed:

[darrachequesne]

@ohabash for the Heroku platform, you can check: https://devcenter.heroku.com/articles/session-affinity

[darrachequesne]

If it’s an HTTP 400 error, it sounds like a “Session ID unknown” error, when some requests reach a different Socket.IO server in a multiple servers setup. Are sticky sessions enabled?

See also: https://socket.io/docs/v4/troubleshooting-connection-issues/