Can I connect to any Unit with Upstream and SignalR?

Question

Hello,

I have a websocket server which handles connection to some devices (from third parties so I don't control their implementation).

My system was working fine with .NET framework on an app service until I figured out that app services have a max outbound IPs of 8000 connections in my case.

I need to move towards a more scalable server which brings me some questions.

My constraints : I need to keep a constant websocket open with the devices and be able to reach them at any time to send them messages (one by one).

I started looking into Azure app service Signal R (or the Web Pub Sub which seems very similar). The code and the pricing seems to fit my needs. Using the upstream feature I could also send custom messages to my devices.

However I don't understand the scaling part, it says each unit can contain 1000 devices.

All my devices are going to connect to myapp.com, 5000 of them so divided in 5 units. They are going to send me messages sent to Azure functions for analysis.

But if I decide to send a message to device n° 4300 do I need to know on which Unit it is? Can I reach it if I have several units?

I couldn't find the answer on azure's docs or signalr.

Thank you for your help

Answer 1

it looks like you are doing your own websocket. web sockets are a persistent connection. when a controller action opens a web socket, that action does not return until the web socket is closed.

typically you would use a static collection tying a particular web socket connection to a an id associated with the client at the other end, if you scale out, then move the static collection to a database, and include the server key. (redis is typically used). then when you want to send a message to a client(s) you lookup in the database, and send a message to the server with the connection, and have the server send the message to the correct web socket. you can use a reshape or have additional web sockets between the servers for server to server communication.

if using signal/r as the hub, then in the action, in addition to a websocket to the client, you would open a connection to the hub. then the action's job is to relay messages between the hub and the client. if the client disconnects be sure to exit the hub.

Answer 2

UMS-2098, I see that you have posted the question on SO, I'd posted

On this 'But if I decide to send a message to device n° 4300 do I need to know on which Unit it is? Can I reach it if I have several units?"

No, you don’t need to. “Unit” here is just some concept to help you understand the capacity of the service.
A service having Unit5 is a service has the ability to handle 5000 concurrent clients." Please also check this doc : Difference between SignalR unit and instance and SignalR pricing

I'd also added this info on your SO thread.

Answer 3

The azure signal/r has a builtin scale out service bus, so it looks like one service. Your application may need to scale out also, so be sure to design state management correctly.