Deploying

Channels 2 (ASGI) applications deploy similarly to WSGI applications - you load them into a server, like Daphne, and you can scale the number of server processes up and down.

The one optional extra requirement for a Channels project is to provision a channel layer. Both steps are covered below.

Configuring the ASGI application

The one setting that Channels needs to run is ASGI_APPLICATION, which tells Channels what the root application of your project is. As discussed in Routing, this is almost certainly going to be your top-level (Protocol Type) router.

It should be a dotted path to the instance of the router; this is generally going to be in a file like myproject/routing.py:

ASGI_APPLICATION = "myproject.routing.application"

Setting up a channel backend

Note

This step is optional. If you aren’t using the channel layer, skip this section.

Typically a channel backend will connect to one or more central servers that serve as the communication layer - for example, the Redis backend connects to a Redis server. All this goes into the CHANNEL_LAYERS setting; here’s an example for a remote Redis server:

CHANNEL_LAYERS = {
    "default": {
        "BACKEND": "channels_redis.core.RedisChannelLayer",
        "CONFIG": {
            "hosts": [("redis-server-name", 6379)],
        },
    },
}

To use the Redis backend you have to install it:

pip install -U channels_redis

Run protocol servers

In order to talk to the outside world, your Channels/ASGI application needs to be loaded into a protocol server. These can be like WSGI servers and run your application in a HTTP mode, but they can also bridge to any number of other protocols (chat protocols, IoT protocols, even radio networks).

All these servers have their own configuration options, but they all have one thing in common - they will want you to pass them an ASGI application to run. Because Django needs to run setup for things like models when it loads in, you can’t just pass in the same variable as you configured in ASGI_APPLICATION above; you need a bit more code to get Django ready.

In your project directory, you’ll already have a file called wsgi.py that does this to present Django as a WSGI application. Make a new file alongside it called asgi.py and put this in it:

"""
ASGI entrypoint. Configures Django and then runs the application
defined in the ASGI_APPLICATION setting.
"""

import os
import django
from channels.routing import get_default_application

os.environ.setdefault("DJANGO_SETTINGS_MODULE", "myproject.settings")
django.setup()
application = get_default_application()

If you have any customizations in your wsgi.py to do additional things on application start, or different ways of loading settings, you can do those in here as well.

Now you have this file, all you need to do is pass the application object inside it to your protocol server as the application it should run:

daphne -p 8001 myproject.asgi:application

HTTP and WebSocket

While ASGI is a general protocol and we can’t cover all possible servers here, it’s very likely you will want to deploy a Channels project to work over HTTP and potentially WebSocket, so we’ll cover that in some more detail.

The Channels project maintains an official ASGI HTTP/WebSocket server, Daphne, and it’s this that we’ll talk about configuring. Other HTTP/WebSocket ASGI servers are possible and will work just as well provided they follow the spec, but will have different configuration.

You can choose to either use Daphne for all requests - HTTP and WebSocket - or if you are conservative about stability, keep running standard HTTP requests through a WSGI server and use Daphne only for things WSGI cannot do, like HTTP long-polling and WebSockets. If you do split, you’ll need to put something in front of Daphne and your WSGI server to work out what requests to send to each (using HTTP path or domain) - that’s not covered here, just know you can do it.

If you use Daphne for all traffic, it auto-negotiates between HTTP and WebSocket, so there’s no need to have your WebSockets on a separate domain or path (and they’ll be able to share cookies with your normal view code, which isn’t possible if you separate by domain rather than path).

To run Daphne, it just needs to be supplied with an application, much like a WSGI server would need to be. Make sure you have an asgi.py file as outlined above.

Then, you can run Daphne and supply the channel layer as the argument:

daphne myproject.asgi:application

You should run Daphne inside either a process supervisor (systemd, supervisord) or a container orchestration system (kubernetes, nomad) to ensure that it gets restarted if needed and to allow you to scale the number of processes.

If you want to bind multiple Daphne instances to the same port on a machine, use a process supervisor that can listen on ports and pass the file descriptors to launched processes, and then pass the file descriptor with --fd NUM.

You can also specify the port and IP that Daphne binds to:

daphne -b 0.0.0.0 -p 8001 myproject.asgi:application

You can see more about Daphne and its options on GitHub.

Alternative Web Servers

There are also alternative ASGI servers that you can use for serving Channels.

To some degree ASGI web servers should be interchangeable, they should all have the same basic functionality in terms of serving HTTP and WebSocket requests.

Aspects where servers may differ are in their configuration and defaults, performance characteristics, support for resource limiting, differing protocol and socket support, and approaches to process management.

You can see more alternative servers, such as Uvicorn, in the ASGI implementations documentation.

Example Setups

These are examples of possible setups - they are not guaranteed to work out of the box, and should be taken more as a guide than a direct tutorial.

Nginx/Supervisor (Ubuntu)

This example sets up a Django site on an Ubuntu server, using Nginx as the main webserver and supervisord to run and manage Daphne.

First, install Nginx and Supervisor:

$ sudo apt install nginx supervisor

Now, you will need to create the supervisor configuration file (often located in /etc/supervisor/conf.d/ - here, we’re making Supervisor listen on the TCP port and then handing that socket off to the child processes so they can all share the same bound port:

[fcgi-program:asgi]
# TCP socket used by Nginx backend upstream
socket=tcp://localhost:8000

# Directory where your site's project files are located
directory=/my/app/path

# Each process needs to have a separate socket file, so we use process_num
# Make sure to update "mysite.asgi" to match your project name
command=daphne -u /run/daphne/daphne%(process_num)d.sock --fd 0 --access-log - --proxy-headers mysite.asgi:application

# Number of processes to startup, roughly the number of CPUs you have
numprocs=4

# Give each process a unique name so they can be told apart
process_name=asgi%(process_num)d

# Automatically start and recover processes
autostart=true
autorestart=true

# Choose where you want your log to go
stdout_logfile=/your/log/asgi.log
redirect_stderr=true

Have supervisor reread and update its jobs:

$ sudo supervisorctl reread
$ sudo supervisorctl update

Next, Nginx has to be told to proxy traffic to the running Daphne instances. Setup your nginx upstream conf file for your project:

upstream channels-backend {
    server localhost:8000;
}
...
server {
    ...
    location / {
        try_files $uri @proxy_to_app;
    }
    ...
    location @proxy_to_app {
        proxy_pass http://channels-backend;

        proxy_http_version 1.1;
        proxy_set_header Upgrade $http_upgrade;
        proxy_set_header Connection "upgrade";

        proxy_redirect off;
        proxy_set_header Host $host;
        proxy_set_header X-Real-IP $remote_addr;
        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
        proxy_set_header X-Forwarded-Host $server_name;
    }
    ...
}

Reload nginx to apply the changes:

$ sudo service nginx reload