NServiceBus: Is the NSB Distributor a bottleneck?

Question

I wanted use a network load balancer to distribute messages, but I understand that it has problems when you are trying use Transactional queue. Now I am planning to use the NSB distributor. Does the distributor host not become a bottleneck like I think it would? I had assumed that the distributor defeats the purpose of scaling out a subscriber because it puts all subscriber instances behind a one-machine bottleneck. Thoughts?

Answer 1

Depending on the throughput of your Distributor you can scale it up with more threads or add another one all together. Since the Distributor is not aware of where its work comes from you can create a grid of Distributors/Workers and scale horizontally as much as you like.

Alternatively you could expose a web service entry point that is load balanced and pushes work to two identical Distributors. We have found that the Distributor can pretty much dish out the work as fast as you push the work to it. It is not doing much, so the heavy lifting is done by the Workers. I would run some tests to see if it meets your needs.

You will want to consider clustering your Distributor as you don't want to lose the body of work the Workers need to do.