Architecting with Channels

Transcript

1. None

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

   at Used to complain about migrations a lot

3. 2010

4. WebSockets

5. WebSockets (and Eventlet)

6. 2012

7. None

8. 2014

9. "django-onair"

10. 2015

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