I think it's all of the above. In large enterprises, there is usually some sort of global message bus on top of Kafka, AWS Kinesis or similar. In smaller shop

I think it's all of the above. In large enterprises, there is usually some sort of global message bus on top of Kafka, AWS Kinesis or similar. In smaller shops, the need for dedicated message bus is over engineering and can be avoided by using the db or something like redis. It is still a message queue, just without a dedicated platform.