Upgrade to Pro
— share decks privately, control downloads, hide ads and more …
Speaker Deck
Features
Speaker Deck
PRO
Sign in
Sign up for free
Search
Search
Channels (Under The Hood)
Search
Andrew Godwin
November 03, 2016
Programming
1
7.5k
Channels (Under The Hood)
A talk I gave at Django Under The Hood 2016.
Andrew Godwin
November 03, 2016
Tweet
Share
More Decks by Andrew Godwin
See All by Andrew Godwin
Reconciling Everything
andrewgodwin
1
310
Django Through The Years
andrewgodwin
0
200
Writing Maintainable Software At Scale
andrewgodwin
0
440
A Newcomer's Guide To Airflow's Architecture
andrewgodwin
0
350
Async, Python, and the Future
andrewgodwin
2
660
How To Break Django: With Async
andrewgodwin
1
720
Taking Django's ORM Async
andrewgodwin
0
720
The Long Road To Asynchrony
andrewgodwin
0
650
The Scientist & The Engineer
andrewgodwin
1
760
Other Decks in Programming
See All in Programming
VS Code Update for GitHub Copilot
74th
1
480
XP, Testing and ninja testing
m_seki
3
220
0626 Findy Product Manager LT Night_高田スライド_speaker deck用
mana_takada
0
130
型付きアクターモデルがもたらす分散シミュレーションの未来
piyo7
0
810
ふつうの技術スタックでアート作品を作ってみる
akira888
0
210
ASP.NETアプリケーションのモダナイズ インフラ編
tomokusaba
1
430
イベントストーミング図からコードへの変換手順 / Procedure for Converting Event Storming Diagrams to Code
nrslib
1
540
Select API from Kotlin Coroutine
jmatsu
1
190
Team topologies and the microservice architecture: a synergistic relationship
cer
PRO
0
1.1k
都市をデータで見るってこういうこと PLATEAU属性情報入門
nokonoko1203
1
580
今ならAmazon ECSのサービス間通信をどう選ぶか / Selection of ECS Interservice Communication 2025
tkikuc
20
3.8k
Result型で“失敗”を型にするPHPコードの書き方
kajitack
4
540
Featured
See All Featured
Designing Dashboards & Data Visualisations in Web Apps
destraynor
231
53k
Code Reviewing Like a Champion
maltzj
524
40k
Git: the NoSQL Database
bkeepers
PRO
430
65k
Rails Girls Zürich Keynote
gr2m
94
14k
Building Applications with DynamoDB
mza
95
6.5k
The Illustrated Children's Guide to Kubernetes
chrisshort
48
50k
How to train your dragon (web standard)
notwaldorf
94
6.1k
Practical Orchestrator
shlominoach
188
11k
It's Worth the Effort
3n
185
28k
Unsuck your backbone
ammeep
671
58k
GraphQLの誤解/rethinking-graphql
sonatard
71
11k
Responsive Adventures: Dirty Tricks From The Dark Corners of Front-End
smashingmag
252
21k
Transcript
None
Andrew Godwin Hi, I'm Django core developer Senior Software Engineer
at Used to complain about migrations a lot
It's magic.
It's magic.
The Problem 1
The Web is changing.
WebSockets
WebSockets WebRTC Long-polling MQTT Server-Sent Events
Python is synchronous. Django is synchronous.
Synchronous code is easier to write. Single-process async is not
enough.
Proven design pattern Not too hard to reason about
What could fit these constraints?
Loose Coupling 2
Not too tied to WebSockets Not too tied to Django
Well-defined, minimal interfaces
Easy to swap out or rewrite
The Message Bus HTTP Server Message Bus WSock Server Django
Project
What do you send? How do you send it?
ASGI
nonblocking send blocking receive add to group discard from group
send to group
JSON-compatible, dictionary-based messages onto named channels
Concrete Ideas 3
Develop using concrete examples
WebSocket connect receive disconnect accept/reject send
WebSocket websocket.connect websocket.send!abc1234 websocket.receive websocket.disconnect
At-most-once First In First Out Backpressure via capacity Not sticky
No guaranteed ordering No serial processing
HTTP & WS Channel Layer Django Worker HTTP & WS
Django Worker Django Worker Django Worker
{ "text": "Hello, world!", "path": "/chat/socket/", "reply_channel": "websocket.send!9m12in2p", }
Developed and spec'd HTTP WebSocket Rough drafts IRC Email Slack
Please, no. Minecraft Mainframe Terminal
{ "reply_channel": "http.response!g23vD2x5", "method": "GET", "http_version": "2", "path": "/chat/socket/", "query_string":
"foo=bar", "headers": [["cookie", "abcdef..."]], }
At-most-once First In First Out Backpressure via capacity Not sticky
No guaranteed ordering No serial processing
At-most-once First In First Out Backpressure via capacity Not sticky
No guaranteed ordering No serial processing
"order" key on receive messages Connection acceptance
Daphne HTTP/WebSocket Server Channels Django integration asgi-redis Redis backend asgi-ipc
Local memory backend asgiref Shared code and libs
Django-ish 4
It can take several tries to get a nice API.
Consumers based on Views Callable that takes an object Decorators
for functionality Class-based generics
@channel_session def chat_receive(message): name = message.channel_session["name"] message.reply_channel.send({"text": "OK"}) Group("chat").send({ "text":
"%s: %s" % (name, message["text"]), }) Message.objects.create( name=name, content=message["text"], )
Routing based on URLs List of regex-based matches Includes with
prefix stripping on paths More standardised interface
routing = [ route( "websocket.receive", consumers.chat_receive, path=r"^/chat/socket/$", ), include("stats.routing", path="^/stats/"),
route_class(ConsumerClass, path="^/v1/"), ]
Sessions are the only state Sessions hang off reply channels
not cookies Uses same sessions backends Available on the consumer's argument Can also access long-term cookie sessions
@enforce_ordering def receive_consumer(message): Log.objects.create(...)
session = session_for_reply_channel( message.reply_channel.name ) if not session.exists(session.session_key): try: session.save(must_create=True)
except CreateError: # Session wasn't unique raise ConsumeLater() message.channel_session = session
No Middleware New-style middleware half works No ability to capture
sends Decorators replace most cases
View/HTTP Django still there Can intermingle or just use one
type View system is just a consumer now
def view_consumer(message): replies = AsgiHandler()(message) for reply in replies: while
True: try: message.reply_channel.send(reply) except ChannelFull: time.sleep(0.05) else: break
Signals and commands runserver works as expected Signals for handling
lifecycle staticfiles configured for development
Beyond 5
Generalised async communication
Service messaging Security/CPU separation Sync & Async / Py2 &
Py3
Diversity of implementations More web servers More channel layers
More optimisation More efficient bulk sends Less network traffic on
receive
More maintainers More viewpoints, more time
1.0 coming soon Stable APIs for everything except binding
Thanks. Andrew Godwin @andrewgodwin channels.readthedocs.io github.com/andrewgodwin/channels-examples