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Architecting with Channels
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Andrew Godwin
July 19, 2016
Programming
2
1.1k
Architecting with Channels
My keynote from DjangoCon US 2016.
Andrew Godwin
July 19, 2016
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Transcript
None
Andrew Godwin Hi, I'm Django core developer Senior Software Engineer
at Used to complain about migrations a lot
2010
WebSockets
WebSockets (and Eventlet)
2012
None
2014
"django-onair"
2015
Channels
Born from WebSockets
Born from WebSockets Expanded to be more
The "real hard problem"
Asynchronous coordination
Why?
WebSockets don't magically solve everything
Architecture is about tradeoffs
Bidirectional, low overhead Complex client-side, compatibility CONS PROS
Streaming updates Chat applications Collaborative editing Game backends
Broadcast
Server Client 1 Client 2 Client 3 Client 4
Server Client 1 Client 2 Client 3 Client 4 Server
Server Client 1 Client 2 Client 3 Client 4 Server
The "hard problem"
Channels is a foundation for runnng 'async' at scale
WebSockets Task offloading Chat/Email integration IoT protocols
What makes it hard?
Stateful connections Internal network Bottlenecks
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"
Server Server Django Script ASGI ASGI ASGI ASGI Redis
Server Server Django Script ASGI ASGI ASGI ASGI Shared Memory
Server Server Django Script ASGI ASGI ASGI ASGI Shared Memory
Redis Redis
bit.ly/asgi-spec
Channels wraps the low-level ASGI operations
Think of it as the "Django bit" of a larger
whole.
Daphne HTTP/WebSocket Server Channels Django integration asgi-redis Redis backend asgi-ipc
Local memory backend asgiref Shared code and libs
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
Putting it to use Let's make a chat!
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
Routing from channels import route routing = [ route("websocket.connect", on_connect),
route("websocket.receive", on_receive), route("websocket.disconnect", on_disconnect) ]
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
Full worked example github.com/andrewgodwin/channels-examples
Liveblog
Liveblog
Data Binding Multiplexing &
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"]
Demo Do I dare?
More in channels-examples!
Custom Protocols
Decompose into messages Email email.send, email.receive Slack slack.receive, slack.send, slack.joined,
... MQTT mqtt.subscribe, mqtt.unsubscribe, mqtt.send, ...
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
Write Django consumers Same codebase as the main project Optional
routing/per-worker channel limiting
IRC Worker ASGI Worker Worker Email MQTT Scheduler HTTP/WS Custom
Daemon
Channels is a tool for you to use
There's more to be done (and some funding for it)
1995 You are a desktop app 2005 You are a
website 2015 You are a rich web/mobile app 2025 ?
What are the goals of a framework? Do we adapt?
Let's keep Django and Python a great choice for complex
backends
Thanks. Andrew Godwin @andrewgodwin channels.readthedocs.io github.com/andrewgodwin/channels-examples