Sockjs/socketio disconnect delay behind apache proxy - node.js

Question

I need to handle users disconnecting from my sockjs application running in xhr-polling mode. When I connect to localhost, everything works as expected. When I put apache between nodejs and browser, I get ~20 sec delay between closed browser and disconnect event inside nodejs. My apache proxy config is following:
<Location />
ProxyPass http://127.0.0.1:8080/
ProxyPassReverse http://127.0.0.1:8080/
</Location>
The rest of the file is default, you can see it here. I tried playing with ttl=2 and timeout=2 options, but either nothing changes, or I get reconnected each 2 seconds without closing browser. How can I reduce additional disconnect timeout, introduced, but apache, somewhere in its defaults?

Answer 1

It's possible that your Apache server is configured to use HTTP Keep Alive which will keep a persistent connection open. In that case I would try disabling KeepAlive, or lowering the KeepAliveTimeout setting in your Apache configuration to see if this solves the problem.
If that doesn't work, I would also take a look at netstat and see what is the status of each socket and start a root cause analysis. This chart gives is the TCP state machine and can tell you where each connection is. Wireshark can also give you some information on what is going on.

Answer 2

In long polling the connection happens like below
<client> ---> apache ---> <node.js>
When client breaks the connection
<client> -X-> apache ---> <node.js>
Apache still keeps the connection open. Now there are two workaround to this
ProxyTimeout
You can add below to your apache config
ProxyTimeout 10
This will break the connection after 10 seconds, but then this break every long polling connection after 10 seconds, which you don't want
Ping
Next option is to ping the client
pingTimeout (Number): how many ms without a pong packet to consider the connection closed (60000)
pingInterval (Number): how many ms before sending a new ping packet (25000).
var io = require('socket.io')(server, { 'transports': ['polling'], pingTimeout: 5000, pingInterval: 2500});
Above will make sure the client is disconnected within 5 seconds of going off, you can lower it again further but then this may impact the usual loading scenarios
But reading through all the posts, threads and sites, I don't think you can replicate the behavior you get when connect to socket.io directly, because the connection break then can be detected easily by socket.io

Answer 3

The 20 sec delay not in the apache proxy. I got the same issue, delay not happening in the local URL, but delay happening in global URL.
The issue was solved in the NodeJs itself. Need to send one time data from server to client to make sure it's initialized. This problem not in the documentation and issues blog at the WebSocket plugin.
Send a dummy message after request accepted in the server, like below.
let connection = request.accept(null, request.origin);
connection.on('message', function (evt) {
console.log(evt);
});
connection.on('close', function (evt) {
console.log(evt);
});
connection.send("Success"); //dummy message to the client from server