Connect to another container using Docker compose

Question

I need to use two containers together: one with Tomcat and another with a Database.

I have created the following yaml file which describes the services:

Answer 1

Use the alias "db" that you have defined in file to refer to the database host name.

Containers for the linked service will be reachable at a hostname identical to the alias, or the service name if no alias was specified.

Source: https://docs.docker.com/compose/compose-file/compose-file-v2/#links