Deploy behind HAProxy - websockets 12.0 documentation
Description: This guide demonstrates a way to load balance connections across multiple websockets server processes running on the same machine with HAProxy. We’ll run server processes with Supervisor as describ...

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# Deploy behind HAProxy

This guide demonstrates a way to load balance connections across multiple websockets server processes running on the same machine with HAProxy.

We’ll run server processes with Supervisor as described in this guide.

## Run server processes

Save this app to `app.py`:

    #!/usr/bin/env python

    import asyncio
    import os
    import signal

    import websockets

    async def echo(websocket):
        async for message in websocket:
            await websocket.send(message)

    async def main():
        # Set the stop condition when receiving SIGTERM.
        loop = asyncio.get_running_loop()
        stop = loop.create_future()
        loop.add_signal_handler(signal.SIGTERM, stop.set_result, None)

        async with websockets.serve(
            echo,
            host="localhost",
            port=8000 + int(os.environ["SUPERVISOR_PROCESS_NAME"][-2:]),
        ):
            await stop

    if __name__ == "__main__":
        asyncio.run(main())

Each server process listens on a different port by extracting an incremental index from an environment variable set by Supervisor.

Save this configuration to `supervisord.conf`:

    [supervisord]

    [program:websockets-test]
    command = python app.py
    process_name = %(program_name)s_%(process_num)02d
    numprocs = 4
    autorestart = true

This configuration runs four instances of the app.

Install Supervisor and run it:

    $ supervisord -c supervisord.conf -n

## Configure and run HAProxy

Here’s a simple HAProxy configuration to load balance connections across four processes:

    defaults
        mode http
        timeout connect 10s
        timeout client 30s
        timeout server 30s

    frontend websocket
        bind localhost:8080
        default_backend websocket

    backend websocket
        balance leastconn
        server websockets-test_00 localhost:8000
        server websockets-test_01 localhost:8001
        server websockets-test_02 localhost:8002
        server websockets-test_03 localhost:8003

In the backend configuration, we set the load balancing method to `leastconn` in order to balance the number of active connections across servers. This is best for long running connections.

Save the configuration to `haproxy.cfg`, install HAProxy, and run it:

    $ haproxy -f haproxy.cfg

You can confirm that HAProxy proxies connections properly:

    $ PYTHONPATH=src python -m websockets ws://localhost:8080/
    Connected to ws://localhost:8080/.
    > Hello!
    < Hello!
    Connection closed: 1000 (OK).