Is there a way to combine Docker images into 1 container?

Question

I have a few Dockerfiles right now.

One is for Cassandra 3.5, and it is FROM cassandra:3.5

I also have a Dockerfile for Kafka, but t is quite a

Answer 1

You could not combine docker images into 1 container. See the detail discussions in Moby issue, How do I combine several images into one via Dockerfile.

For your case, it is better to not include the whole Cassandra and Kafka images. The application would only need the Cassandra Scala driver and Kafka Scala driver. The container should include the drivers only.