mirror of
https://github.com/django/daphne.git
synced 2025-04-25 03:03:47 +03:00
100 lines
4.0 KiB
ReStructuredText
100 lines
4.0 KiB
ReStructuredText
Channel Layer Types
|
|
===================
|
|
|
|
Multiple choices of backend are available, to fill different tradeoffs of
|
|
complexity, throughput and scalability. You can also write your own backend if
|
|
you wish; the spec they confirm to is called :doc:`ASGI <asgi>`. Any
|
|
ASGI-compliant channel layer can be used.
|
|
|
|
Redis
|
|
-----
|
|
|
|
The Redis layer is the recommended backend to run Channels with, as it
|
|
supports both high throughput on a single Redis server as well as the ability
|
|
to run against a set of Redis servers in a sharded mode.
|
|
|
|
To use the Redis layer, simply install it from PyPI (it lives in a separate
|
|
package, as we didn't want to force a dependency on the redis-py for the main
|
|
install):
|
|
|
|
pip install -U asgi_redis
|
|
|
|
By default, it will attempt to connect to a Redis server on ``localhost:6379``,
|
|
but you can override this with the ``hosts`` key in its config::
|
|
|
|
CHANNEL_LAYERS = {
|
|
"default": {
|
|
"BACKEND": "asgi_redis.RedisChannelLayer",
|
|
"ROUTING": "???",
|
|
"CONFIG": {
|
|
"hosts": [("redis-channel-1", 6379), ("redis-channel-2", 6379)],
|
|
},
|
|
},
|
|
}
|
|
|
|
Sharding
|
|
~~~~~~~~
|
|
|
|
The sharding model is based on consistent hashing - in particular,
|
|
:ref:`response channels <channel-types>` are hashed and used to pick a single
|
|
Redis server that both the interface server and the worker will use.
|
|
|
|
For normal channels, since any worker can service any channel request, messages
|
|
are simply distributed randomly among all possible servers, and workers will
|
|
pick a single server to listen to. Note that if you run more Redis servers than
|
|
workers, it's very likely that some servers will not have workers listening to
|
|
them; we recommend you always have at least ten workers for each Redis server
|
|
to ensure good distribution. Workers will, however, change server periodically
|
|
(every five seconds or so) so queued messages should eventually get a response.
|
|
|
|
Note that if you change the set of sharding servers you will need to restart
|
|
all interface servers and workers with the new set before anything works,
|
|
and any in-flight messages will be lost (even with persistence, some will);
|
|
the consistent hashing model relies on all running clients having the same
|
|
settings. Any misconfigured interface server or worker will drop some or all
|
|
messages.
|
|
|
|
|
|
Database
|
|
--------
|
|
|
|
The database layer is intended as a short-term solution for people who can't
|
|
use a more production-ready layer (for example, Redis), but still want something
|
|
that will work cross-process. It has poor performance, and is only
|
|
recommended for development or extremely small deployments.
|
|
|
|
This layer is included with Channels; just set your ``BACKEND`` to
|
|
``channels.database_layer.DatabaseChannelLayer``, and it will use the
|
|
default Django database alias to store messages. You can change the alias
|
|
by setting ``CONFIG`` to ``{'alias': 'aliasname'}``.
|
|
|
|
.. warning::
|
|
The database channel layer is NOT fast, and performs especially poorly at
|
|
latency and throughput. We recommend its use only as a last resort, and only
|
|
on a database with good transaction support (e.g. Postgres), or you may
|
|
get errors with multiple message delivery.
|
|
|
|
|
|
In-memory
|
|
---------
|
|
|
|
The in-memory layer is only useful when running the protocol server and the
|
|
worker server in a single process; the most common case of this
|
|
is ``runserver``, where a server thread, this channel layer, and worker thread all
|
|
co-exist inside the same python process.
|
|
|
|
Its path is ``asgiref.inmemory.ChannelLayer``. If you try and use this channel
|
|
layer with ``runworker``, it will exit, as it does not support cross-process
|
|
communication.
|
|
|
|
|
|
Writing Custom Channel Layers
|
|
-----------------------------
|
|
|
|
The interface channel layers present to Django and other software that
|
|
communicates over them is codified in a specification called :doc:`ASGI <asgi>`.
|
|
|
|
Any channel layer that conforms to the :doc:`ASGI spec <asgi>` can be used
|
|
by Django; just set ``BACKEND`` to the class to instantiate and ``CONFIG`` to
|
|
a dict of keyword arguments to initialize the class with.
|