What is the difference between docker-compose and gitlab ci services?

Question

GitLab

Stupid question, but I can't figure it out. Both allow you to manage an application from multiple images, right? Now, if I have a dependence on the DBMS, where should I register it? In services? In .docker-compose.yml?

Answer 1

docker-compose is a tool for creating composition from
gitlab docker containers ci services is a thing for bringing up some services available during the ci/cd process

Both allow you to manage an application from multiple images, right?

No, that's not true - only docker-compose does this.
Basically, they are designed to solve completely different tasks.
In short, you are trying to compare warm with soft.

Now, if I have a dependence on the DBMS, where should I register it? In services? In .docker-compose.yml?

If this dependency occurs at the testing stage, then yes - in services.
If this dependency occurs at the production stage, then you need to deal with the production environment, and not with the gitlab, including compose, if you use it.