> Or just freaking MQTT.

Disclaimer: I'm a dev and I'm not very familiar with the actual maintenance of kafka clusters. But we run the aws managed service version (MSK), and it seems to just pretty much work.

We send terrabytes of data through kafka asynchronously, because of its HA properties and persistent log, allowing consumers to consume in their own time and put the data where it needs to be. So imagine, many apps across our entire stack have the same basic requirement, publish a lot of data which people want to analyse somewhere later. Kafka gives us a single mechanism to do that.

So now my question. I've never used MQTT before. What are the benefits of using MQTT in our setup vs using kafka?

I use MQTT daily. I'm not sure why the commenter suggested it; it is orthogonal to queueing or log streams.

MQTT is a publish/subscribe protocol for large scale distributed messaging, often used in small embedded devices or factories. It is made for efficient transfer of small, often byte sized payloads of IoT device data. It does not replace Kafka or RabbitMQ - messages should be read off of the MQTT broker as quickly as possible. ( I know this from experience - MQTT brokers get bogged down rapidly if there are too many messages "in flight")

A very common pattern is to use MQTT for communications, and then Kafka or RabbitMq for large scale queuing of those messages for downstream applications.