Reinventing Django for the Real-Time Web

Transcript

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   Andrew Godwin @andrewgodwin Reinventing REAL-TIME WEB for the

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   Andrew Godwin Hi, I'm Django core developer Senior Software Engineer

   at Likes complaining about networking
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   Django, HTTP and WSGI

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   You take a request... ...and return a response.

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   Browser HTTP Webserver Django WSGI View Handler

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   HTTP 1 request response Browser Server request response request response

   request response
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   HTTP 2 request response Browser Server request response request 1

   response 2 request 2 response 1
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   WebSockets receive send Browser Server send receive send send receive

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   ???

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    Easy to use Secure by default Hard to break/deadlock Python

    2 & 3 compatible Optional
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    Python Concurrency & Message-passing Django not being async

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    WSGI Server HTTP WSGI WSGI App WSGI Server HTTP WSGI

    WSGI App Process 1 Process 2
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    Worker Protocol Server WebSocket Process 1 Worker Worker Worker Protocol

    Server WebSocket Process 2 Worker
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    Protocol Server WebSocket Process 1 Worker Protocol Server WebSocket Process

    2
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    Channel Layer Interface Server Worker Server Process 1 ASGI ASGI

    Asynchronous socket handling Synchronous Django project Interface Server Worker Server ASGI ASGI Worker Server ASGI Process 2 Process 3 Process 4
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    Channel Layer Worker Server Interface Server Channel Layer Worker Server

    Interface Server Channel Layer Worker Server Interface Server Channel Layer Worker 1 Worker 2 Worker 3 Redis
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    Groups Channels Named FIFO task queues Named sets of channels

    you broadcast to
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    send("channel_name", {"ponies": True}) receive_many(["channel_name", "channel_two"]) send_group("group_name", {"ponies": True}) group_add("group_name", "channel_name")

    group_discard("group_name", "channel_name")
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    You take a request... ...and return a response.

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    You receive a message... ...and send zero or more messages.

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    View Request Response Consumer Message Messages

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    Consumer websocket.connect Consumer websocket.receive websocket.send

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    Consumer websocket.connect Consumer websocket.receive websocket.send!jq3x41

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    Consumer http.request http.response!a34cxw

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    websocket.receive Worker Worker Worker websocket.send!a1b2c3 Socket

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    Receive events from channels, and send events to them/groups. WebSocket/HTTP

    messages come with a reply_channel
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    Using it

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    Installation pip install channels Add channels to INSTALLED_APPS

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    Liveblog We want people to get new blog posts as

    they are published, without refreshing
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    Liveblog People open a WebSocket when they open the page

    Their WebSocket is added to a group When the BlogPost model is saved, we send the post to that group
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    Their WebSocket is added to a group When the BlogPost

    model is saved, we send the post to that group def ws_connect(message): Group("liveblog").add(message.reply_channel) class BlogPost(models.Model): ... def save(self, *args, **kwargs): ... Group("liveblog").send({ "text": json.dumps({"id": self.id}), })
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    Chat People can send messages, and they get sent to

    everyone connected.
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    Chat When people connect they join a chat group When

    we receive a message we send it to the group
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    When people connect they join a chat group def ws_connect(message):

    Group("chat").add(message.reply_channel) When we receive a message we send it to the group def ws_receive(message): Group("chat").send({ "text": message["text"], })
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    ...and we tell Django what consumers are joined to which

    actions. # in routing.py routing = [ route("websocket.connect", consumers.ws_connect), route("websocket.receive", consumers.ws_receive), ] ...and we tell Django what consumers are joined to which actions.
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    Important notes Runserver just works with WebSockets now Generic Consumers

    exist Fully worked versions of these two are at github.com/andrewgodwin/channels-examples Django sessions + auth work with WebSockets
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    FIFO queue with send and receive_many operations, named with a

    string. Channel Group Named set of channels with add/remove/send operations Cross-process Messages Representations for HTTP and WebSocket sessions
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    ASGI API specification for channel layer backends Message formats for

    HTTP and WebSocket &
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    Redis POSIX IPC In-memory Reference network layer For single-machine installs

    For testing or single-process installs
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    Channel Layer Interface Server Worker Server Process 1 ASGI ASGI

    Asynchronous socket handling Synchronous Django project Interface Server Worker Server ASGI ASGI Worker Server ASGI Process 2 Process 3 Process 4
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    Channel Layer Interface Server Worker Server Channel Layer Daphne HTTP

    + WS WSGI Adapter HTTP asgi_redis Cross-network, shards asgi_ipc Single-machine Django Consumer system WSGI Adapter Most WSGI apps
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    WSGI and/or ASGI An ASGI system can serve HTTP and

    WebSocket ...or your WSGI system can send onto channels
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    Channel Layer Worker Server Interface Server Channel Layer Worker Server

    Interface Server WSGI App WSGI Server Channel Layer Worker 1 Worker 2 Worker 3 Redis
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    Scaling?

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    Interface servers scale horizontally Worker servers scale horizontally Channel layer

    has to as well
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    Consistent hash sharding designed in Other approaches possible

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    Looking Ahead

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    Being Django Official external app Merge in 1.11 or 2.0

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    Maturity Load tests and tweaking Learning from production installs

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    Community Third-party tools and extensions Tutorials, write-ups and case studies

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    Co-existence Not everyone needs WebSockets! Make sure it's easy to

    add or remove.
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    Expansion Email, chat and other message formats Add more events

    to code against!
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    Specification ASGI is not Django-specific WSGI needs supplementing for new

    protocols
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    channels.readthedocs.io github.com/andrewgodwin/channels-examples

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    Thanks. Andrew Godwin @andrewgodwin