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.

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