Architecting with Channels

Transcript

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   Andrew Godwin Hi, I'm Django core developer Senior Software Engineer

   at Used to complain about migrations a lot
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   2010

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   WebSockets

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   WebSockets (and Eventlet)

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   2012

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   None
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   2014

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   "django-onair"

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    2015

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    Channels

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    Born from WebSockets

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    Born from WebSockets Expanded to be more

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    The "real hard problem"

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    Asynchronous coordination

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    Why?

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    WebSockets don't magically solve everything

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    Architecture is about tradeoffs

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    Bidirectional, low overhead Complex client-side, compatibility CONS PROS

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    Streaming updates Chat applications Collaborative editing Game backends

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    Broadcast

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    Server Client 1 Client 2 Client 3 Client 4

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    Server Client 1 Client 2 Client 3 Client 4 Server

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    Server Client 1 Client 2 Client 3 Client 4 Server

    The "hard problem"
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    Channels is a foundation for runnng 'async' at scale

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    WebSockets Task offloading Chat/Email integration IoT protocols

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    What makes it hard?

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    Stateful connections Internal network Bottlenecks

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    Server Server Django Script ASGI "Send to channel X" "Receive

    from channel X" "Send to group Y" "Add channel X to group Y" "Remove channel X from group Y"
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    Server Server Django Script ASGI ASGI ASGI ASGI Redis

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    Server Server Django Script ASGI ASGI ASGI ASGI Shared Memory

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    Server Server Django Script ASGI ASGI ASGI ASGI Shared Memory

    Redis Redis
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    bit.ly/asgi-spec

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    Channels wraps the low-level ASGI operations

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    Think of it as the "Django bit" of a larger

    whole.
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    Daphne HTTP/WebSocket Server Channels Django integration asgi-redis Redis backend asgi-ipc

    Local memory backend asgiref Shared code and libs
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    What does Channels provide? Routing Consumers Sessions Auth Helpers By

    channel, URL, etc. Standardised message handling Cross-network persistence on sockets Including HTTP cookies on WebSocket runserver, runworker, debugging info
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    Putting it to use Let's make a chat!

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    Consumers def on_connect(message): Group("chat").add(message.reply_channel) def on_receive(message): Group("chat").send({"text": message["text"]}) def on_disconnect(message):

    Group("chat").discard(message.reply_channel) websocket.connect websocket.receive websocket.disconnect
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    Routing from channels import route routing = [ route("websocket.connect", on_connect),

    route("websocket.receive", on_receive), route("websocket.disconnect", on_disconnect) ]
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    Class-based from channels import route_class routing = [ route_class(ChatConsumer), ]

    from channels.generic.websockets class ChatConsumer(WebsocketConsumer): def connection_groups(self): return ["chat"] def receive(self, text): self.group_send("chat", text=text) Routing
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    Full worked example github.com/andrewgodwin/channels-examples

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    Liveblog

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    Liveblog

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    Data Binding Multiplexing &

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    class IntegerValue(models.Model): name = models.CharField(max_length=100, unique=True) value = models.IntegerField(default=0) class

    IntegerValueBinding(WebsocketBinding): model = IntegerValue stream = "intval" def check_permission(self, user, action, instance): return True def group_names(self, instance, action): return ["binding.values"]
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    Demo Do I dare?

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    More in channels-examples!

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    Custom Protocols

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    Decompose into messages Email email.send, email.receive Slack slack.receive, slack.send, slack.joined,

    ... MQTT mqtt.subscribe, mqtt.unsubscribe, mqtt.send, ...
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    Write a custom server Use asyncio, Twisted, Gevent, etc Server

    takes path to ASGI channel layer instance (CLI/config file) Roll layer.send, layer.receive_many into your event loop
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    Write Django consumers Same codebase as the main project Optional

    routing/per-worker channel limiting
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    IRC Worker ASGI Worker Worker Email MQTT Scheduler HTTP/WS Custom

    Daemon
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    Channels is a tool for you to use

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    There's more to be done (and some funding for it)

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    1995 You are a desktop app 2005 You are a

    website 2015 You are a rich web/mobile app 2025 ?
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    What are the goals of a framework? Do we adapt?

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    Let's keep Django and Python a great choice for complex

    backends
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    Thanks. Andrew Godwin @andrewgodwin channels.readthedocs.io github.com/andrewgodwin/channels-examples