Load balance WebSocket connections to Tornado app using HAProxy?

haproxy, nginx, proxy, tornado, websocket

Solution

it's not difficult to implement WebSocket in haproxy, though I admit it's not yet easy to find doc on this (hopefully this response will make one example). If you're using haproxy 1.4 (which I suppose you are) then it works just like any other HTTP request without having to do anything, as the HTTP Upgrade is recognized by haproxy.

If you want to direct the WebSocket traffic to a different farm than the rest of HTTP, then you should use content switching rules, in short :

 frontend pub-srv
    bind :80
    use_backend websocket if { hdr(Upgrade) -i WebSocket }
    default_backend http

 backend websocket
    timeout server 600s
    server node1 1.1.1.1:8080 check
    server node2 2.2.2.2:8080 check

 backend http
    timeout server 30s
    server www1 1.1.1.1:80 check
    server www2 2.2.2.2:80 check

If you're using 1.5-dev, you can even specify "timeout tunnel" to have a larger timeout for WS connections than for normal HTTP connections, which saves you from using overly long timeouts on the client side.

You can also combine Upgrade: WebSocket + a specific URL :

 frontend pub-srv
    bind :80
    acl is_websocket hdr(Upgrade) -i WebSocket
    acl is_ws_url path /something1 /something2 /something3
    use_backend websocket if is_websocket is_ws_url
    default_backend http

Last, please don't use the stupid 24h idle timeouts we sometimes see, it makes absolutely no sense to wait for a client for 24h with an established session right now. The web is much more mobile than in the 80s and connection are very ephemeral. You'd end up with many FIN_WAIT sockets for nothing. 10 minutes is already quite long for the current internet.

Hoping this helps!

Problem

I am working on a Tornado app that uses websocket handlers. I'm running multiple instances of the app using Supervisord, but I have trouble load balancing websocket connections. I know nginx does not support dealing with websockets out of the box, but I followed the instructions here http://www.letseehere.com/reverse-proxy-web-sockets to use the nginx tcp_proxy module to reverse proxy websocket connections. However, this did not work since the module can't route websocket urls (ex: ws://localhost:80/something). So it would not work with the URL routes I have defined in my Tornado app. From my research around the web, it seems that HAProxy is the way to go to load balance my websocket connections. However, I'm having trouble finding any decent guidance to setup HAProxy to load balance websocket connections and also be able to handle websocket URL routes. I would really appreciate some detailed directions on how to get this going. I am also fully open to other solutions as well.

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