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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.
.. _Supervisor: http://supervisord.org/
We'll bind all servers to the same port. The OS will take care of balancing
connections.
Create and activate a virtualenv:
.. code-block:: console
$ python -m venv supervisor-websockets
$ . supervisor-websockets/bin/activate
Install websockets and Supervisor:
.. code-block:: console
$ pip install websockets
$ pip install supervisor
Save this app to a file called ``app.py``:
.. literalinclude:: ../../example/deployment/supervisor/app.py
This is an echo server with two features added for the purpose of this guide:
* It shuts down gracefully when receiving a ``SIGTERM`` signal;
* It enables the ``reuse_port`` option of :meth:`~asyncio.loop.create_server`,
which in turns sets ``SO_REUSEPORT`` on the accept socket.
Save this Supervisor configuration to ``supervisord.conf``:
.. literalinclude:: ../../example/deployment/supervisor/supervisord.conf
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:
.. code-block:: console
$ 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:
.. code-block:: console
$ 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:
.. code-block:: console
$ kill -TERM 43597
The logs show that Supervisor restarted this instance:
.. code-block:: console
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:
.. code-block:: console
$ python -m websockets ws://localhost:8080/
Connected to ws://localhost:8080/.
>
Look at the pid of supervisord itself in the logs and terminate it:
.. code-block:: console
$ kill -TERM 43596
The logs show that Supervisor terminated all instances of the app before
exiting:
.. code-block:: console
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:
.. code-block:: console
$ 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.
* Add ``environment=PATH="path/to/your/virtualenv/bin"`` in the Supervisor
configuration. Then ``python app.py`` runs in that virtualenv.
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