Djangocon: building real-time apps with django - Iacopo Spalletti¶

Tags: djangocon, django

(One of my summaries of a talk at the 2018 european djangocon.)

The web isn’t a pure request/response web anymore. There’s real-time web now. There are lots of tools (yeah!), but you also get lots of complexity (booo!).

Django channels is a framework to use django in the non-http world. Websockets, but not only those. Channels (version 1) is out now for three years, version 2 came out a few months ago. The talk assumes version 2.

Some concepts:

• Asynchronous. For us, this means event-driven. A problem is that asynchronous code is normally harder to understand because of its non-linear nature.

  But… channels hides most of the complexity for you.

• ASGI. A protocol spec (like WSGI), independent of channels.

  It is ASGI all the way down. You can nest them.

• Protocol server. This implements the ASGI spec for a specific protocol. It interacts with the connection. It bridges the network and the application.

  For channels, this often is ‘daphne’.

• Routing. Maps incoming messages to consumers. It is nestable and composable.

• Scope. A “scope” is created for every connection. It holds the data of the connection.

• Channel. IPC mechanism (“Inter Process Communication”). FIFO “at-most-once” queue.

• Consumers. The core abstraction to build an ASGI app. It handles events on a connection. It is stateful: every individual connection is connected to an individual consumer.

  Note on stateful: everything runs in a single process.

• Events. Triggered during a “scope”. In the end, consumers consume events.

• Frontend. Often: websockets, which means javascript.

He showed a demo and then some code. (I couldn’t type over the example code, of course :-) ).

• First you’ll define “channel layers” in your settings. A queue somewhere, for instance.

• Next some routing. Paths are mapped to consumers.

• Next some consumers. For instance a websocket consumer. You can have methods like connect(), disconnect() and receive(... event ...).

• A bit of javascript for the websocket frontend.

Summary of channels:

• Async is made easier.

• You still have access to the django API.

Photo explanation: interiors means something like this. The office of the manager.