I've used both and NATS is definitely what I'd pick starting out. RabbitMQ is great too, but its heavier and harder to configure. Federation is the killer feature of RabbitMQ that NATS doesn't really have (afaik?).
I've never used RabbitMQ, but NATS supports clustering, super clustering, and leaf node connections. I'm guessing the latter is the closest to what would be considered "federation" in this context.
None of them are close. RabbitMQ has traffic shaping, MQ->MQ routing (federation), and all sorts of stuff that is super important if you use it as a generalized routing system (vs plain IP). NATS doesn't have that and it's almost certainly firmly out of scope.
When you say "MQ->MQ routing (federation)" I have a hard time understanding how that is not close to leaf nodes. Leaf nodes allow independently operated / managed NATS servers to share data back and forth, which to me is what federation is about. Do you have any resources you recommend to help me grasp why this is different?
Oh cool, I didn't know it could! Regardless, advanced routing is still something that RabbitMQ has that isn't in NATS. It's not useful for every system, but it is a differentiator. I usually reach for NATS + Jetstream these days, with its object and KV systems it's a really great "all-in-one" for basic stuff.
NATS JetStream has equivalent functionality to federation out of the box with stream sourcing, combined with super-clustering and leaf-nodes. You can have streams that source and combine messages (with filters and subject transformation) from other sources and that sourcing happens in a 'guaranteed store and forward' manner, even if for example the stream being sourced is located in another cluster in a different region or provider or in an edge device (running a leaf node) that has only partial network connectivity (e.g. on a vehicle) and completely different security setup.
(for more detail check out this and the other YouTube videos on the Synadia channel https://youtu.be/WH55czo1BNk)
