In Azure Web PubSub, How to receive messages in backend microservice for processing

Question

Requirement:

My clients are using simple WebSocket connection to send messages. I want to receive these messages inside my backend .NET 8 web api and process them further to send fine-tuned data to some distributed cache services.

From documentation, I only understood that I can use backend to only send the Access URL with token to clients, and Hubs are for dealing with events only (not messages).

I don't see how to receive messages in the backend service itself, but I guess I will need to use 'WebPubSubClient' in backend service itself to receive & process messages.

Doubt:

• For receiving messages, how to set up a WebSocket connection from backend service?
• If not, Is it right approach to use Client SDK to receive messages in web api service (probably using it in continuous running hosted service) ?

Answer 1

in general a websocket connection is persistent connection rather than a typical http request/response. It is a 2 way stream with no formal packet definition. Part of designing a websocket app is defining the packet structures.

signal/r is a communication library and protocol built on websockets. It implements common HUBs for the server side and supports packet routing. unless your clients are already using signal/r this is not an option.

you can easily code to receive raw messages. You code would replace the echo method:

https://learn.microsoft.com/en-us/aspnet/core/fundamentals/websockets?view=aspnetcore-9.0

your clients will need to tell you what the packets structure is and any required protocol packets.

as hosting a websocket application requires a persistent connections to multiple clients, and typically there are dedicated resources for each connection, which is active for the life of the connection. so a websocket app ties up more resources than a standard website (which typically have a 90 second connection time limit) thus require a different hosting requirement. But azure web apps support websockets by default now.

the Azure Web PubSub is an optimized hosting option for websocket applications. but it does not control how the app is developed or tools, but supplies a library to simplify websocket programming. it supports .net, node, python, java and azure functions (via hooks).