Overview of DJANGO Channels

1. DJANGO CHANNELS
by Chew Kok Hoor kokhoor@solutionx.com.

2. About Me
 Also Director of Third Life Sdn. Bhd. – co-
developer of Mobile Marketing app for Businesses:
channels.io
 Web Applications - Django
 Mobile Apps backend - Django
 Point-of-Sales system (POS) - Django
 POS Device Connectors - Tornado.

3. Objective
 General overview of Channels
 Simple Example
 Scaling

4. What is Django Channels
“Channels is a project to make Django able to
handle more than just plain HTTP requests,
including WebSockets and HTTP2, as well as the
ability to run code after a response has been sent for
things like thumbnailing or background calculation.”
- http://channels.readthedocs.io/

5. Web Applications Activities /
Tasks
 Respond to request (GET, POST, …)
 Batch activities – slower tasks such as sending
email etc.
 Web Sockets

6. Python Frameworks / Libraries
 Respond to request (GET, POST, …)
 DJANGO
 Batch processing
 Celery, RQ, Gearman
 Web Sockets
 Flask, Tornado, Twisted

7. Vanilla Django
 Built around
Requests and
Responses
 Incompatible with
WebSockets.
Source:
https://blog.heroku.com/in_deep_with_django_channels_the_future_of_real_time_apps_in_django

8. Django Channels
 Addition of Async Interface
Server and Channels Layer
(Asynchronous Server
Gateway Interface)
 Worker Processes able to
handle Request / Response,
WebSocket and Background
Processes
 Existing concepts of views still
applies to Request &
Response
Source:
https://blog.heroku.com/in_deep_with_django_channels_the_future_of_real_time_apps_in_django

9. Side-by-Side
Vanilla Django Django
Daphne
In-Memory /
IPC / Redis

10. Why Django Channels?
 Pros
 Consolidate and centralize configuration and program code
 Easier re-use
 Asynchronous in nature but you still write synchronous code
– no yields, monkey-patching etc.
 In one big package, so improvements and directions can be
aligned.
 Cons
 Celery more complete compared to what Channels has to
offer
 Channels Layer choices still limited (IPC, Redis)
 Stuck in an Opinionated Framework

11. Example app for Django
Channels
 Borrowed code from
https://github.com/jacobian/chann
els-example/
 Covers:
 Traditional Request Response
(TemplateViews)
 Batch (fake email sending)
 WebSockets

12. Getting Started
 pip install channels
 pip install asgi_redis
 settings.py
CHANNEL_LAYERS = {
"default": {
"BACKEND": "asgi_redis.RedisChannelLayer",
"CONFIG": {
"hosts": [‘redis://localhost:6379’],
},
"ROUTING": "main.routing.default_routing",
}
}

13. Routing
routing.py
from channels.routing import route
from . import consumers
from . import batch
channel_routing = [
route('send-invite', batch.send_invite),
]
chat_routing = [
route('websocket.connect', consumers.ws_connect),
route('websocket.receive', consumers.ws_receive),
route('websocket.disconnect', consumers.ws_disconnect),
]
default_routing = channel_routing + chat_routing

14. asgi.py
import os
import channels.asgi
os.environ.setdefault("DJANGO_SETTINGS_MODULE",
"channels_test.settings")
channel_layer = channels.asgi.get_channel_layer()

15. Excerpt of views.py
class InviteView(TemplateView):
template_name = "invite.html"
def post(self, request, *args, **kwargs):
context = self.get_context_data()
REQUEST_DATA = request.POST
email = REQUEST_DATA.get('email')
if not email:
context['error'] = "Email field not provided"
return super(TemplateView, self).render_to_response(context)
data = {
'email': email,
'message': u"Hi, %s, you're invited!! Check us out at http://www.solutionx.com.my for more
info!" % email
}
Channel('send-invite', alias=settings.BATCH_CHANNEL_LAYER).send(data)
context['message'] = "We're sending the invite for you!"
return super(TemplateView, self).render_to_response(context)

16. batch.py
import logging
import time
logger = logging.getLogger('email')
def send_invite(message):
logger.info("We receive a request to send email to: " +
message.get('email'))
logger.info("Message: " + message.get('message'))
time.sleep(10)
logger.info("Email sent successfully!")

17. Running the processes
1. redis-server
2. daphne main.asgi:channel_layer
3. python manage.py runworker

18. Scaling
1. Add more workers
1. Redis sharding (seems to still require further
testing)
2. Multiple Channel Layers

19. Scaling
1. Add more workers
- python manage.py runworker

20. Scaling (2)
1. Redis sharding (still requires further testing)

21. Redis Sharding
CHANNEL_LAYERS = {
"default": {
"BACKEND": "asgi_redis.RedisChannelLayer",
"CONFIG": {
"hosts": ['redis://localhost:6379',
'redis://localhost:7777'],
},
"ROUTING": "main.routing.default_routing",
}
}

22. Running the processes
(Sharding)
1. redis-server
2. redis-server --port 7777
3. daphne main.asgi_sharding:channel_layer
4. python manage.py runworker --settings
channels_test.settings_sharding
5. python manage.py runworker --settings
channels_test.settings_sharding

23. Scaling (3)
1. Multiple Channel Layers

24. Multiple Channel Layers
CHANNEL_LAYERS = {
"test": {
"BACKEND": "asgi_redis.RedisChannelLayer",
"CONFIG": {
"hosts": [‘redis://localhost:6379’],
},
"ROUTING": "main.routing.channel_routing",
},
"chat": {
"BACKEND": "asgi_redis.RedisChannelLayer",
"CONFIG": {
"hosts": [`redis://localhost:7777’],
},
"ROUTING": "main.routing.chat_routing",
},
}

25. Running the processes (Multiple
Channel Layers)
1. redis-server
2. redis-server --port 7777
3. daphne -b 0.0.0.0 -p 8000 main.asgi_test:channel_layer
4. python manage.py runworker --settings
channels_test.settings_prod --layer test --only-channels
http.request
5. python manage.py runworker --settings
channels_test.settings_prod --layer test --only-channels
send-invite
6. daphne -b 0.0.0.0 -p 8080 main.asgi_chat:channel_layer
7. python manage.py runworker --settings
channels_test.settings_prod --layer chat

26. Wrapping Up
 New but promising
 Hopefully makes writing complex web apps
easier
 References:
 https://blog.heroku.com/in_deep_with_django_channe
ls_the_future_of_real_time_apps_in_django
 http://www.machinalis.com/blog/introduction-to-
django-channels/
 http://channels.readthedocs.io/en/latest/
 https://github.com/andrewgodwin/channels

27. Q&A
Chew Kok Hoor
Director
kokhoor@solutionx.com.my
iOS
channels.io App (not related to Django Channels, name
similarity purely co-incidental)
http://channels.io
Android