[mtw]

What kind of companies or startups usually use this service?

[rhodin]

Companies dealing with large amounts of data. A list with some companies using Apache Kafka can be found here: https://cwiki.apache.org/confluence/display/KAFKA/Powered+By

[mtw]

thanks. I guess my sites are not big enough (yet)

[poooogles]

It's pretty big in ad tech, or anywhere that really does lots and lots of centralised logging (Datadog/Loggly both use Kafka).

Lots of places also use it just as a message queue, some places for example write time series metrics to Kafka for monitoring.