If I'm not buying a message bus in as a service, then NATS is great for pub/sub and or message passing system it is simple to configure, has good documentation

If I'm not buying a message bus in as a service, then NATS is great for pub/sub and or message passing system it is simple to configure, has good documentation, and excellent integration into most languages. It guarantees uptime, and thats about it. It clusters really well, so you can swap out instances, or scale in/out as you need.