Deploy with Supervisor#
This guide proposes a simple way to deploy a websockets server directly on a Linux or BSD operating system.
We’ll configure Supervisor to run several server processes and to restart them if needed.
We’ll bind all servers to the same port. The OS will take care of balancing connections.
Create and activate a virtualenv:
$ python -m venv supervisor-websockets $ . supervisor-websockets/bin/activate
Install websockets and Supervisor:
$ pip install websockets $ pip install supervisor
Save this app to a file called
#!/usr/bin/env python import asyncio 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="", port=8080, reuse_port=True, ): await stop if __name__ == "__main__": asyncio.run(main())
This is an echo server with two features added for the purpose of this guide:
It shuts down gracefully when receiving a
It enables the
create_server(), which in turns sets
SO_REUSEPORTon the accept socket.
Save this Supervisor configuration to
[supervisord] [program:websockets-test] command = python app.py process_name = %(program_name)s_%(process_num)02d numprocs = 4 autorestart = true
This is the minimal configuration required to keep four instances of the app running, restarting them if they exit.
Now start Supervisor in the foreground:
$ supervisord -c supervisord.conf -n INFO Increased RLIMIT_NOFILE limit to 1024 INFO supervisord started with pid 43596 INFO spawned: 'websockets-test_00' with pid 43597 INFO spawned: 'websockets-test_01' with pid 43598 INFO spawned: 'websockets-test_02' with pid 43599 INFO spawned: 'websockets-test_03' with pid 43600 INFO success: websockets-test_00 entered RUNNING state, process has stayed up for > than 1 seconds (startsecs) INFO success: websockets-test_01 entered RUNNING state, process has stayed up for > than 1 seconds (startsecs) INFO success: websockets-test_02 entered RUNNING state, process has stayed up for > than 1 seconds (startsecs) INFO success: websockets-test_03 entered RUNNING state, process has stayed up for > than 1 seconds (startsecs)
In another shell, after activating the virtualenv, we can connect to the app — press Ctrl-D to exit:
$ python -m websockets ws://localhost:8080/ Connected to ws://localhost:8080/. > Hello! < Hello! Connection closed: 1000 (OK).
Look at the pid of an instance of the app in the logs and terminate it:
$ kill -TERM 43597
The logs show that Supervisor restarted this instance:
INFO exited: websockets-test_00 (exit status 0; expected) INFO spawned: 'websockets-test_00' with pid 43629 INFO success: websockets-test_00 entered RUNNING state, process has stayed up for > than 1 seconds (startsecs)
Now let’s check what happens when we shut down Supervisor, but first let’s establish a connection and leave it open:
$ python -m websockets ws://localhost:8080/ Connected to ws://localhost:8080/. >
Look at the pid of supervisord itself in the logs and terminate it:
$ kill -TERM 43596
The logs show that Supervisor terminated all instances of the app before exiting:
WARN received SIGTERM indicating exit request INFO waiting for websockets-test_00, websockets-test_01, websockets-test_02, websockets-test_03 to die INFO stopped: websockets-test_02 (exit status 0) INFO stopped: websockets-test_03 (exit status 0) INFO stopped: websockets-test_01 (exit status 0) INFO stopped: websockets-test_00 (exit status 0)
And you can see that the connection to the app was closed gracefully:
$ python -m websockets ws://localhost:8080/ Connected to ws://localhost:8080/. Connection closed: 1001 (going away).
In this example, we’ve been sharing the same virtualenv for supervisor and websockets.
In a real deployment, you would likely:
Install Supervisor with the package manager of the OS.
Create a virtualenv dedicated to your application.
environment=PATH="path/to/your/virtualenv/bin"in the Supervisor configuration. Then
python app.pyruns in that virtualenv.