Kristian Øllegaard presented an approach for implementing real-time web applications using Django. He discussed using Node.js with Socket.io for the real-time capabilities and Redis for cross-language communication between the Node.js and Django applications. He demonstrated publishing messages from Django to a Redis queue that the Node.js application subscribed to and then emitted to the browser via Socket.io, providing real-time updates. While the approach can be used today, he cautioned against doing so without further work on aspects like client authentication.

1. Implementing real time web
applications with Django
Kristian Øllegaard
1
onsdag den 6. juni 12

2. About me
• Software Developer/System Administrator at Divio
• Django since 0.96
• Danish, lived in Zurich 1,5 year
@oellegaard
github.com/KristianOellegaard
2
onsdag den 6. juni 12

3. Why real time?
• Better user experience
• More options in front end
• Make the web feel like native apps
• Showing live data.
• Collaboration is much easier.
@oellegaard
github.com/KristianOellegaard
3
onsdag den 6. juni 12

4. Finding the right tool
• Criteria's
• Use websockets, but have fallbacks
• Good browser support (incl. old IE)
• Should be usable from python
• Does not require extensive changes in frontend
• “As fast as it can be”
@oellegaard
github.com/KristianOellegaard
4
onsdag den 6. juni 12

5. The tools you want
Node.js + Socket.io
@oellegaard
github.com/KristianOellegaard
5
onsdag den 6. juni 12

6. The tools you want
Node.js + Socket.io
(well, we don’t want this, but socket.io needs it)
@oellegaard
github.com/KristianOellegaard
5
onsdag den 6. juni 12

7. The tools you want
• Node.js
• Built on Chrome's JavaScript runtime
• Uses an event-driven, non-blocking I/O model
• Socket.io
• One interface for all transport methods (sockets, polling, etc.)
• Compatible with almost everything
@oellegaard
github.com/KristianOellegaard
6
onsdag den 6. juni 12

8. Why not implement it in Python?
• Already active community
• Can be used from python without too much trouble
• Most people know very basic javascript
• More importantly, frontend engineers, knows javascript and can
therefore contribute to the different browser-specific
implementations.
@oellegaard
github.com/KristianOellegaard
7
onsdag den 6. juni 12

9. Using redis for cross-language
communication
• Support for many datatypes
• Can be used both as storage and as a queue
• Implemented in many different languages
• For the usage in this talk, any other queue could have been used as
well.
@oellegaard
github.com/KristianOellegaard
8
onsdag den 6. juni 12

10. Basic concept
• Something happens, the user
Redis
must be notified in real time publish publish
•
subscribe
From e.g. django we insert the
E.g.
new value into the queue Django Node.js
Celery
• Node.js listens on the queue subscribe
and emits any content directly Browser
to the browser via socket.io
• This is btw. very fast!
@oellegaard
github.com/KristianOellegaard
9
onsdag den 6. juni 12

11. Sample node.js app
var io = require('socket.io').listen(8001);
var redis = require('redis').createClient();
redis.psubscribe("socketio_*"); // Could be any pattern
io.sockets.on('connection', function (socket) {
redis.on('pmessage', function(pattern, channel, key){
socket.emit(channel, key);
});
});
@oellegaard
github.com/KristianOellegaard
10
onsdag den 6. juni 12

12. Sample HTML/JS
<script src="http://localhost:8001/socket.io/socket.io.js"></script>
<script>
var socket = io.connect('http://localhost:8001/');
socket.on('socketio_news', function (data) {
console.log(data);
});
</script>
@oellegaard
github.com/KristianOellegaard
11
onsdag den 6. juni 12

13. Sample usage from Python
import redis
import json
redis_subscribe = redis.StrictRedis()
redis_subscribe.publish("socketio_news", json.dumps({
'title': 'Djangocon 2012',
}))
@oellegaard
github.com/KristianOellegaard
12
onsdag den 6. juni 12

14. Short demo
@oellegaard
github.com/KristianOellegaard
13
onsdag den 6. juni 12

15. Hosting socket.io
• Nginx does not support websockets!
• Needs its own app, if hosted on an application cloud (e.g. heroku)
• Recommended to expose the node server directly
• But hey, it’s node.js, it scales!
@oellegaard
github.com/KristianOellegaard
14
onsdag den 6. juni 12

16. Can I use this today?
• Yes
• But, please don’t
@oellegaard
github.com/KristianOellegaard
15
onsdag den 6. juni 12

17. Client Authentication
• Socket.io handles authentication from node -> client
• Currently no authentication between django and node.
• Could possibly be solved by storing your sessions in redis and
checking them on connection.
@oellegaard
github.com/KristianOellegaard
16
onsdag den 6. juni 12

18. Notes
• Concept should work with any language/framework
• E.g. communicating between ruby and python
@oellegaard
github.com/KristianOellegaard
17
onsdag den 6. juni 12

19. Questions?
http://kristian.io
@oellegaard
@oellegaard
github.com/KristianOellegaard
18
onsdag den 6. juni 12