Implementing real time web applications with Django

Implementing real time web
applications with Django
Kristian Øllegaard

1
onsdag den 6. juni 12

About me

• Software Developer/System Administrator at Divio

• Django since 0.96

• Danish, lived in Zurich 1,5 year

@oellegaard
github.com/KristianOellegaard
2

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
3

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
4

The tools you want

Node.js + Socket.io

@oellegaard
5

The tools you want

Node.js + Socket.io
(well, we don’t want this, but socket.io needs it)

@oellegaard
5

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
6

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
7

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
8

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
9

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
10

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
11

Sample usage from Python

import redis
import json
redis_subscribe = redis.StrictRedis()
redis_subscribe.publish("socketio_news", json.dumps({
'title': 'Djangocon 2012',
}))

@oellegaard
12

Short demo

@oellegaard
13

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
14

Can I use this today?

• Yes

• But, please don’t

@oellegaard
15

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
16

Notes

• Concept should work with any language/framework

• E.g. communicating between ruby and python

@oellegaard
17

Questions?

http://kristian.io
@oellegaard

@oellegaard
18

Implementing real time web applications with Django

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