You’ve pretty much got it. If you really have a need to have two separate services processing the data this way, then that’s exactly how you approach it.
producer -> topicA -> service1 -> topicB -> service2
service1 is both reading and writing to Kafka, it is both a consumer and a producer. That’s really all the Kafka Streams library is. It’s an abstraction for cases where you’re both a consumer and producer.
Just a quick note about separating the processing into two separate services this way:
There are definitely pros and cons to this architecture, so consider it carefully. If you decide to have multiple services handle this pipeline of processing, you need to deploy and manage more services. There’s a definitive cost to that. That cost may be outweighed by the ability to reprocess parts of your pipeline or by the ability to deploy updates to different parts of the pipeline independently.