Architecting with Channels

My keynote from DjangoCon US 2016.

2. Andrew Godwin Hi, I'm Django core developer Senior Software Engineer at Used to complain about migrations a lot
4. WebSockets
5. WebSockets (and Eventlet)
9. "django-onair"
11. Channels
12. Born from WebSockets
13. Born from WebSockets Expanded to be more
14. The "real hard problem"
15. Asynchronous coordination
16. Why?
17. WebSockets don't magically solve everything
18. Architecture is about tradeoffs
19. Bidirectional, low overhead Complex client-side, compatibility CONS PROS
20. Streaming updates Chat applications Collaborative editing Game backends
21. Broadcast
22. Server Client 1 Client 2 Client 3 Client 4
23. Server Client 1 Client 2 Client 3 Client 4 Server
24. Server Client 1 Client 2 Client 3 Client 4 Server The "hard problem"
25. Channels is a foundation for runnng 'async' at scale
26. WebSockets Task offloading Chat/Email integration IoT protocols
27. What makes it hard?
28. Stateful connections Internal network Bottlenecks
29. 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"
30. Server Server Django Script ASGI ASGI ASGI ASGI Redis
31. Server Server Django Script ASGI ASGI ASGI ASGI Shared Memory
32. Server Server Django Script ASGI ASGI ASGI ASGI Shared Memory Redis Redis
33. bit.ly/asgi-spec
34. Channels wraps the low-level ASGI operations
35. Think of it as the "Django bit" of a larger whole.
36. Daphne HTTP/WebSocket Server Channels Django integration asgi-redis Redis backend asgi-ipc Local memory backend asgiref Shared code and libs
37. 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
38. Putting it to use Let's make a chat!
39. 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
40. Routing from channels import route routing = [ route("websocket.connect", on_connect), route("websocket.receive", on_receive), route("websocket.disconnect", on_disconnect) ]
41. 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
42. Full worked example github.com/andrewgodwin/channels-examples
43. Liveblog
44. Liveblog
45. Data Binding Multiplexing &
46. 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"]
47. Demo Do I dare?
48. More in channels-examples!
49. Custom Protocols
50. Decompose into messages Email email.send, email.receive Slack slack.receive, slack.send, slack.joined, ... MQTT mqtt.subscribe, mqtt.unsubscribe, mqtt.send, ...
51. 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
52. Write Django consumers Same codebase as the main project Optional routing/per-worker channel limiting
53. IRC Worker ASGI Worker Worker Email MQTT Scheduler HTTP/WS Custom Daemon
54. Channels is a tool for you to use
55. There's more to be done (and some funding for it)
56. 1995 You are a desktop app 2005 You are a website 2015 You are a rich web/mobile app 2025 ?
57. What are the goals of a framework? Do we adapt?
58. Let's keep Django and Python a great choice for complex backends
59. Thanks. Andrew Godwin @andrewgodwin channels.readthedocs.io github.com/andrewgodwin/channels-examples