Apache Kafka vs MySQL

Apache Kafka and MySQL are free.

Apache Kafka

Free

A log that services publish events to, and other services read later.

Pros of Apache Kafka

Producers do not wait on every downstream service
You can replay events after a bug
It holds up once you actually have a stream of events

Cons of Apache Kafka

Running a cluster is a lot for one app
A database is the simpler choice until you need a stream

MySQL

Free

The relational database behind a huge share of web apps and WordPress.

Pros of MySQL

Easy to find hosting
Familiar SQL
Free Community edition

Cons of MySQL

Fewer advanced features than Postgres
Oracle steers the project