Deploying¶

Configuring the ASGI application¶

As discussed in Installation and Routing, you will have a file like myproject/asgi.py that will define your root application. This is almost certainly going to be your top-level (Protocol Type) router.

Here’s an example of what that asgi.py might look like:

import os

from django.conf.urls import url
from django.core.asgi import get_asgi_application

# Fetch Django ASGI application early to ensure AppRegistry is populated
# before importing consumers and AuthMiddlewareStack that may import ORM
# models.
os.environ.setdefault("DJANGO_SETTINGS_MODULE", "mysite.settings")
django_asgi_app = get_asgi_application()

from channels.auth import AuthMiddlewareStack
from channels.routing import ProtocolTypeRouter, URLRouter

from chat.consumers import AdminChatConsumer, PublicChatConsumer

application = ProtocolTypeRouter({
    # Django's ASGI application to handle traditional HTTP requests
    "http": django_asgi_app,

    # WebSocket chat handler
    "websocket": AuthMiddlewareStack(
        URLRouter([
            url(r"^chat/admin/$", AdminChatConsumer.as_asgi()),
            url(r"^chat/$", PublicChatConsumer.as_asgi()),
        ])
    ),
})

Setting up a channel backend¶

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. All you need to do is pass the application object inside your project’s asgi.py file 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 ASGI application 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.

$ sudo apt install nginx supervisor

[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

$ sudo mkdir /run/daphne/

$ sudo chown <user>.<group> /run/daphne/

$ d /run/daphne 0755 <user> <group>

$ sudo supervisorctl reread
$ sudo supervisorctl update

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;
    }
    ...
}

$ sudo service nginx reload