Django and the Real-time Web

Transcript

1. Django and the Real-Time Web Zachary Voase DjangoCon Europe 2012

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2. WWW: A Changelog IE Chrome 0% 35.0% 70.0% Jul 2008

   Apr 2009 Jan 2010 Oct 2010 Jul 2011 Apr 2012 gs.statcounter.com WebSocket Backbone #NewTwitter Google Instant Basecamp Next NodeJS pjax Google Wave Facebook socket.io Chrome Nitro JägerMonkey Trello

3. “Now, here, you see, it takes all the running you

   can do, to keep in the same place. If you want to get somewhere else, you must run at least twice as fast as that!”

4. • UI before technology • Proactive, not reactive • Synchronized

   with the ‘real world’ What I Talk About When I Talk About Real-Time

5. Three Stories

6. MVC

7. MVC • Trygve Reenskaug et al. @ PARC, ’78/79 •

   Originally a part of Smalltalk-80 • Now the dominant UI design pattern

8. MVC Controller View Model

9. Multi-MVC C V M C V M C V M

10. MVC • Start application • Within event loop: • Receive

    user and network events • Dispatch to controller • Read/write to models • Render views to display • Shut down application

11. MVC on the Web Controller View Model Server Browser

12. MVC on the Web • Listen for requests: • Load

    session state for this user: • Process forms & user input • Read/write to/from database • Render views (HTML, XML, JSON) • Return response • Persist session state, clean up objects

13. REST

14. REST • REpresentational State Transfer • Roy T. Fielding, 2000

    (§5) • Descriptive, not prescriptive

15. REST / /login /about-us /home Invalid Valid Click Click

16. REST • Client-server • Stateless • Cacheable • Layered •

    Code-on-demand (optional) • Uniform

17. WebSocket(s) • Real TCP connection • ‘Magic’ HTTP request to

    port 80 • Reduces latency • Enables real-time push

18. REST & WebSockets • Full-duplex communication: client-server • Long-running connections:

    stateless • Direct TCP connection: layered, cacheable • Ad hoc protocols over WS: uniform

19. FYI: #! belongs in 1 place:

20. #!/bin/sh

21. Version Control

22. Centralised VCS Server Alice Bob

23. Distributed VCS Carol Alice Bob

24. Synthesis

25. Controller View Model Server Browser

26. Controller Alice Model Bob Carol Server

27. C V M C V M C V M Server

    Bob Alice

28. IMAP SMTP

29. IMAP SMTP

30. C V M C V M C V M Server

    Bob Alice PUT /polls/123 PUT /polls/123

31. C V M C V M C V M Server

    Bob Alice PUT /polls/123 PUT /polls/123

32. C V M C V M C V M Server

    Bob Alice PUT /polls/123 PUT /polls/123

33. { "method": "PUT", "resource": "/polls/123", "content": { "name": "Favourite Beer",

    "created": "2012-06-04T10:50:00" } }

34. • Read RFC 2616 • Seriously. • Etags • Cache-Control

    Caching

35. Conflict Resolution

36. (uri, etag, dirty?) Conflict Resolution

37. Conflict Resolution if not uri: CREATE elif is_dirty: # I've

    made local changes if local_etag == remote_etag: OK else: CONFLICT else: if local_etag == remote_etag: NOOP else: REDOWNLOAD

38. Implications • Assumption of orthogonality • Lossless representations • Authn

    & authz • Pub/sub • Resource-oriented client

39. Pub/sub • AMQP • ØMQ • Django signals

40. Barriers • Django ORM • Content negotiation • JavaScript •

    Proxies & middleware

41. Questions? @zacharyvoase