Keep getting and posting /socket.io/?EIO=3&transport=polling&t=

My backend in ExpressJS and NodeJS used to work well. I just realized that logs exploded the disk (the backend is still functional), because when the backend is on, it keeps trying:

kpi.js GET /socket.io/?EIO=3&transport=polling&t=NBiaEK6
index.js GET /socket.io/?EIO=3&transport=polling&t=NBiaEK6
index.js router.get *
kpi.js POST /socket.io/?EIO=3&transport=polling&t=NBiaER6
index.js POST /socket.io/?EIO=3&transport=polling&t=NBiaER6
Error: Not Found
    at /opt/funfun/app.js:99:13
    at Layer.handle [as handle_request] (/opt/funfun/node_modules/express/lib/router/layer.js:95:5)
    at trim_prefix (/opt/funfun/node_modules/express/lib/router/index.js:317:13)
    at /opt/funfun/node_modules/express/lib/router/index.js:284:7
    at Function.process_params (/opt/funfun/node_modules/express/lib/router/index.js:335:12)
    at next (/opt/funfun/node_modules/express/lib/router/index.js:275:10)
    at /opt/funfun/node_modules/express/lib/router/index.js:635:15
    at next (/opt/funfun/node_modules/express/lib/router/index.js:260:14)
    at /opt/funfun/routes/index.js:18:2
    at Layer.handle [as handle_request] (/opt/funfun/node_modules/express/lib/router/layer.js:95:5)
    at trim_prefix (/opt/funfun/node_modules/express/lib/router/index.js:317:13)
    at /opt/funfun/node_modules/express/lib/router/index.js:284:7
    at Function.process_params (/opt/funfun/node_modules/express/lib/router/index.js:335:12)
    at next (/opt/funfun/node_modules/express/lib/router/index.js:275:10)
    at Function.handle (/opt/funfun/node_modules/express/lib/router/index.js:174:3)
    at router (/opt/funfun/node_modules/express/lib/router/index.js:47:12)
    at Layer.handle [as handle_request] (/opt/funfun/node_modules/express/lib/router/layer.js:95:5)
    at trim_prefix (/opt/funfun/node_modules/express/lib/router/index.js:317:13)
    at /opt/funfun/node_modules/express/lib/router/index.js:284:7
    at Function.process_params (/opt/funfun/node_modules/express/lib/router/index.js:335:12)
    at next (/opt/funfun/node_modules/express/lib/router/index.js:275:10)
    at /opt/funfun/node_modules/express/lib/router/index.js:635:15
kpi.js GET /socket.io/?EIO=3&transport=polling&t=NBiaF8A
index.js GET /socket.io/?EIO=3&transport=polling&t=NBiaF8A
index.js router.get *
kpi.js POST /socket.io/?EIO=3&transport=polling&t=NBiaFFz
index.js POST /socket.io/?EIO=3&transport=polling&t=NBiaFFz
Error: Not Found
    at /opt/funfun/app.js:99:13
    at Layer.handle [as handle_request] (/opt/funfun/node_modules/express/lib/router/layer.js:95:5)
    at trim_prefix (/opt/funfun/node_modules/express/lib/router/index.js:317:13)
    at /opt/funfun/node_modules/express/lib/router/index.js:284:7
    at Function.process_params (/opt/funfun/node_modules/express/lib/router/index.js:335:12)
    at next (/opt/funfun/node_modules/express/lib/router/index.js:275:10)
    at /opt/funfun/node_modules/express/lib/router/index.js:635:15
    at next (/opt/funfun/node_modules/express/lib/router/index.js:260:14)
    at /opt/funfun/routes/index.js:18:2
    at Layer.handle [as handle_request] (/opt/funfun/node_modules/express/lib/router/layer.js:95:5)
    at trim_prefix (/opt/funfun/node_modules/express/lib/router/index.js:317:13)
    at /opt/funfun/node_modules/express/lib/router/index.js:284:7
    at Function.process_params (/opt/funfun/node_modules/express/lib/router/index.js:335:12)
    at next (/opt/funfun/node_modules/express/lib/router/index.js:275:10)
    at Function.handle (/opt/funfun/node_modules/express/lib/router/index.js:174:3)
    at router (/opt/funfun/node_modules/express/lib/router/index.js:47:12)
    at Layer.handle [as handle_request] (/opt/funfun/node_modules/express/lib/router/layer.js:95:5)
    at trim_prefix (/opt/funfun/node_modules/express/lib/router/index.js:317:13)
    at /opt/funfun/node_modules/express/lib/router/index.js:284:7
    at Function.process_params (/opt/funfun/node_modules/express/lib/router/index.js:335:12)
    at next (/opt/funfun/node_modules/express/lib/router/index.js:275:10)
    at /opt/funfun/node_modules/express/lib/router/index.js:635:15

kpi.js GET ... and index.js GET ... are what I print. Here is the code of opt/funfun/app.js:

// catch 404 and forward to error handler
app.use(function (req, res, next) {
  var err = new Error('Not Found');  // line 99
  err.status = 404;
  next(err);
});

Does anyone know what may be the reason?

[darrachequesne]

@AvalancheAccessories this is the configuration for NginX, used as a reverse proxy in front of your Socket.IO server(s)

Reference: https://socket.io/docs/v4/reverse-proxy/#nginx

Regarding the initial issue, the multiple requests might be due to a v2 client which tries to connect.

For v3 and above, you need to enable backward compatible mode on the server side:

import { Server } from "socket.io";

const io = new Server({
  allowEIO3: true
});

Reference: https://socket.io/docs/v4/server-options/#alloweio3

You can check those specific errors by listening to the connection_error event:

io.engine.on("connection_error", (err) => {
  if (err.code === 5) {
    // Unsupported protocol version
  }
});

Reference: https://socket.io/docs/v4/server-api/#event-connection_error

[ven]

Hi,

Try this:

server {
    listen 80;
    server_name YOURDOMAIN.COM;
    client_max_body_size 100M;
    location /socket.io/ {
        proxy_http_version 1.1;
        proxy_set_header Upgrade $http_upgrade;
        proxy_set_header Connection "Upgrade";
        proxy_set_header Host $host;
        proxy_pass http://localhost:PORTNUMBER/socket.io/;
    }
}