django/channels_redis

channels_redis

.. image:: https://github.com/django/channels_redis/workflows/Tests/badge.svg :target: https://github.com/django/channels_redis/actions?query=workflow%3ATests

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Provides Django Channels channel layers that use Redis as a backing store.

There are two available implementations:

• RedisChannelLayer is the original layer, and implements channel and group handling itself.
• RedisPubSubChannelLayer is newer and leverages Redis Pub/Sub for message dispatch. This layer is currently at Beta status, meaning it may be subject to breaking changes whilst it matures.

Both layers support a single-server and sharded configurations.

channels_redis is tested against Python 3.9 to 3.13. We test with the latest redis-py version, as well as the older 5.x branch and main development branch, using the latest stable Python and Channels versions. We test the Channels development branch, using the latest stable Python and the latest redis-py release.

Installation

.. code-block::

pip install channels-redis

Note: Prior versions of this package were called asgi_redis and are still available under PyPI as that name if you need them for Channels 1.x projects. This package is for Channels 2 projects only.

Usage

Set up the channel layer in your Django settings file like so:

.. code-block:: python

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

Or, you can use the alternate implementation which uses Redis Pub/Sub:

.. code-block:: python

CHANNEL_LAYERS = {
    "default": {
        "BACKEND": "channels_redis.pubsub.RedisPubSubChannelLayer",
        "CONFIG": {
            "hosts": [("localhost", 6379)],
        },
    },
}

Possible options for CONFIG are listed below.

hosts

The server(s) to connect to, as either URIs, ``(host, port)`` tuples, or dicts conforming to `redis Connection <https://redis.readthedocs.io/en/stable/connections.html#async-client>`_.
Defaults to ``redis://localhost:6379``. Pass multiple hosts to enable sharding,
but note that changing the host list will lose some sharded data.

SSL connections that are self-signed (ex: Heroku):

.. code-block:: python

    "default": {
        "BACKEND": "channels_redis.pubsub.RedisPubSubChannelLayer",
        "CONFIG": {
            "hosts":[{
                "address": "rediss://user@host:port",  # "REDIS_TLS_URL"
                "ssl_cert_reqs": None,
            }]
        }
    }

Sentinel connections require dicts conforming to:

.. code-block::

    {
        "sentinels": [
            ("localhost", 26379),
        ],
        "master_name": SENTINEL_MASTER_SET,
        **kwargs
    }

note the additional ``master_name`` key specifying the Sentinel master set and any additional connection kwargs can also be passed. Plain Redis and Sentinel connections can be mixed and matched if
sharding.

If your server is listening on a UNIX domain socket, you can also use that to connect: ``["unix:///path/to/redis.sock"]``.
This should be slightly faster than a loopback TCP connection.

``prefix``

Prefix to add to all Redis keys. Defaults to asgi. If you're running two or more entirely separate channel layers through the same Redis instance, make sure they have different prefixes. All servers talking to the same layer should have the same prefix, though.

expiry

Message expiry in seconds. Defaults to ``60``. You generally shouldn't need
to change this, but you may want to turn it down if you have peaky traffic you
wish to drop, or up if you have peaky traffic you want to backlog until you
get to it.

``group_expiry``

Group expiry in seconds. Defaults to 86400. Channels will be removed from the group after this amount of time; it's recommended you reduce it for a healthier system that encourages disconnections. This value should not be lower than the relevant timeouts in the interface server (e.g. the --websocket_timeout to daphne <https://github.com/django/daphne>_).

capacity

Default channel capacity. Defaults to ``100``. Once a channel is at capacity,
it will refuse more messages. How this affects different parts of the system
varies; a HTTP server will refuse connections, for example, while Django
sending a response will just wait until there's space.

``channel_capacity``

Per-channel capacity configuration. This lets you tweak the channel capacity based on the channel name, and supports both globbing and regular expressions.

It should be a dict mapping channel name pattern to desired capacity; if the dict key is a string, it's intepreted as a glob, while if it's a compiled re object, it's treated as a regular expression.

This example sets http.request to 200, all http.response! channels to 10, and all websocket.send! channels to 20:

.. code-block:: python

CHANNEL_LAYERS = {
    "default": {
        "BACKEND": "channels_redis.core.RedisChannelLayer",
        "CONFIG": {
            "hosts": [("localhost", 6379)],
            "channel_capacity": {
                "http.request": 200,
                "http.response!*": 10,
                re.compile(r"^websocket.send\!.+"): 20,
            },
        },
    },
}

If you want to enforce a matching order, use an OrderedDict as the argument; channels will then be matched in the order the dict provides them.

.. _encryption:

symmetric_encryption_keys

Pass this to enable the optional symmetric encryption mode of the backend. To
use it, make sure you have the ``cryptography`` package installed, or specify
the ``cryptography`` extra when you install ``channels-redis``::

    pip install channels-redis[cryptography]

``symmetric_encryption_keys`` should be a list of strings, with each string
being an encryption key. The first key is always used for encryption; all are
considered for decryption, so you can rotate keys without downtime - just add
a new key at the start and move the old one down, then remove the old one
after the message expiry time has passed.

Data is encrypted both on the wire and at rest in Redis, though we advise
you also route your Redis connections over TLS for higher security; the Redis
protocol is still unencrypted, and the channel and group key names could
potentially contain metadata patterns of use to attackers.

Keys **should have at least 32 bytes of entropy** - they are passed through
the SHA256 hash function before being used as an encryption key. Any string
will work, but the shorter the string, the easier the encryption is to break.

If you're using Django, you may also wish to set this to your site's
``SECRET_KEY`` setting via the ``CHANNEL_LAYERS`` setting:

.. code-block:: python

    CHANNEL_LAYERS = {
        "default": {
            "BACKEND": "channels_redis.core.RedisChannelLayer",
            "CONFIG": {
                "hosts": ["redis://:[email protected]:6379/0"],
                "symmetric_encryption_keys": [SECRET_KEY],
            },
        },
    }

``on_disconnect`` / ``on_reconnect``

The PubSub layer, which maintains long-running connections to Redis, can drop messages in the event of a network partition. To handle such situations the PubSub layer accepts optional arguments which will notify consumers of Redis disconnect/reconnect events. A common use-case is for consumers to ensure that they perform a full state re-sync to ensure that no messages have been missed.

.. code-block:: python

CHANNEL_LAYERS = {
    "default": {
        "BACKEND": "channels_redis.pubsub.RedisPubSubChannelLayer",
        "CONFIG": {
            "hosts": [...],
            "on_disconnect": "redis.disconnect",
        },
    },
}

And then in your channels consumer, you can implement the handler:

.. code-block:: python

async def redis_disconnect(self, *args):
    # Handle disconnect

serializer_format

By default every message sent to redis is encoded using `msgpack <https://msgpack.org/>`_ (_currently ``msgpack`` is a mandatory dependency of this package, it may become optional in a future release).
It is also possible to switch to `JSON <http://www.json.org/>`_:

.. code-block:: python

    CHANNEL_LAYERS = {
        "default": {
            "BACKEND": "channels_redis.core.RedisChannelLayer",
            "CONFIG": {
                "hosts": ["redis://:[email protected]:6379/0"],
                "serializer_format": "json",
            },
        },
    }


Custom serializers can be defined by:

- extending ``channels_redis.serializers.BaseMessageSerializer``, implementing ``as_bytes `` and ``from_bytes`` methods
- using any class which accepts generic keyword arguments and provides ``serialize``/``deserialize`` methods

Then it may be registered (or can be overriden) by using ``channels_redis.serializers.registry``:

.. code-block:: python

    from channels_redis.serializers import registry

    class MyFormatSerializer:
        def serialize(self, message):
            ...
        def deserialize(self, message):
            ...

    registry.register_serializer('myformat', MyFormatSerializer)

**NOTE**: the registry allows you to override the serializer class used for a specific format without any check nor constraint. Thus it is recommended that to pay particular attention to the order-of-imports when using third-party serializers which may override a built-in format.


Serializers are also responsible for encryption using *symmetric_encryption_keys*. When extending  ``channels_redis.serializers.BaseMessageSerializer`` encryption is already configured in the base class, unless you override the ``serialize``/``deserialize`` methods: in this case you should call ``self.crypter.encrypt`` in serialization and ``self.crypter.decrypt`` in deserialization process. When using a fully custom serializer, expect an optional sequence of keys to be passed via ``symmetric_encryption_keys``.


Dependencies
------------

Redis server >= 5.0 is required for `channels-redis`. Python 3.8 or higher is required.


Used commands
~~~~~~~~~~~~~

Your Redis server must support the following commands:

* ``RedisChannelLayer`` uses ``BZPOPMIN``, ``DEL``, ``EVAL``, ``EXPIRE``,
  ``KEYS``, ``PIPELINE``, ``ZADD``, ``ZCOUNT``, ``ZPOPMIN``, ``ZRANGE``,
  ``ZREM``, ``ZREMRANGEBYSCORE``

* ``RedisPubSubChannelLayer`` uses ``PUBLISH``, ``SUBSCRIBE``, ``UNSUBSCRIBE``

Local Development
-----------------

You can run the necessary Redis instances in Docker with the following commands:

.. code-block:: shell

    $ docker network create redis-network
    $ docker run --rm \
        --network=redis-network \
        --name=redis-server \
        -p 6379:6379 \
        redis
    $ docker run --rm \
        --network redis-network \
        --name redis-sentinel \
        -e REDIS_MASTER_HOST=redis-server \
        -e REDIS_MASTER_SET=sentinel \
        -e REDIS_SENTINEL_QUORUM=1 \
        -p 26379:26379 \
        bitnami/redis-sentinel

Contributing
------------

Please refer to the
`main Channels contributing docs <https://github.com/django/channels/blob/master/CONTRIBUTING.rst>`_.
That also contains advice on how to set up the development environment and run the tests.

Maintenance and Security
------------------------

To report security issues, please contact [email protected]. For GPG
signatures and more security process information, see
https://docs.djangoproject.com/en/dev/internals/security/.

To report bugs or request new features, please open a new GitHub issue.

This repository is part of the Channels project. For the shepherd and maintenance team, please see the
`main Channels readme <https://github.com/django/channels/blob/master/README.rst>`_.