We would love to use Kafka because of its extensive support (e.g. Debezium) and by creating a new Nest.js plugin it would be pretty easy to switch as the message bus is just an implementation detail, nonetheless, we decided to start with NATS because of its much smaller size and RAM requirements making it much better to use for smaller projects (e.g. when firing up a Docker image or running in a small Kubernetes cluster). As an added bonus, NATS is also faster.