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I'm a part of building a service controlling Ev Charging Stations. The protocol is called OCPP and the underlying transport protocol is web sockets.

The stations are calling the host and the web socket is then being upheld, both server and client are initiating commands.

We have implemented the protocol and all that, the question we're looking into is how do we scale and host the web sockets (pressure load of with queue, etc is not the question).

We're currently on Azure and we have in our prototypes used Azure App Service which works fine, however, we have presently not looked into the limitations when it comes to scaling.

We have looked at Azure Pub Sub, however, it doesn't seem compatible with OCPP.

The question is what type of hosting we should look for to host the web sockets?

NPehrsson
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The documentation says that the number of Websockets is unlimited starting with the Standard plan but take a good look at the side note:

If you scale an app in the Basic tier to two instances, you have 350 concurrent connections for each of the two instances. For Standard tier and above, there are no theoretical limits to web sockets, but other factors can limit the number of web sockets. For example, maximum concurrent requests allowed (defined by maxConcurrentRequestsPerCpu) are: 7,500 per small VM, 15,000 per medium VM (7,500 x 2 cores), and 75,000 per large VM (18,750 x 4 cores).

CSharpRocks
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  • I assume the maximum for Azure Web Apps is the maxConcurrentRequestsPerCpu due to that a WebSocket is similar to a request that doesn't close. Or am I'm mistaken? The question still remains are Azure Web Apps a good service to use for this? – NPehrsson Aug 28 '22 at 21:35