Max IEndpointInstances per process

Is there an upper limit to the number of unique IEndpointInstances that be hosted within in a single process?

I'm considering a design that will see up to a 100 unique IEndpointInstances, all listening on separate queues, be active simultaneously.

Will this cause a problem for NServiceBus? Could the process deadlock or spin up so many threads as to be unresponsive and useless?

The question NServiceBus - How to get separate queue for each message type receiver subscribes to? seems to suggest that you can not have multiple endpoints in a process, but this is an older post. I have built a small sample against NServiceBus 6--beta4 that does work.

There is a similar question NServiceBus Single Process, but Multiple Input queues that concluded, based on the OP's context using Satellite Features was the recommended approach. However, in my case, I have 100 (functionally different) sagas (1 per queue), where each saga could need to receive similar messages, but I need to make sure that only the correct saga receives the message. Therefor, I don't think implementing a custom feature will meet my requirements. Or will Satellite Features support Sagas?

Solution

One of the options is to use self multi hosting. Using this approach, you self the endpoints yourself in the same process. There are a few things to take into consideration, such as:

Assembly scanning (might require custom scanning logic per endpoint).
Throughput (for heavy throughput endpoints I'd recommend a separate hosting process).
To update/redeploy a single endpoint, you'll be taking all of the other 99 endpoints down as well.

While there's no hard limit on how many endpoints can be co-hosted, 100 sounds a bit a lot. Saying that, it also depends how heavy the load on those endpoints is. If you process 1 msg/sec or 1K msg/sec determine a lot if this is a viable option or not.

Have a look at the sample that does exactly that.