playbook.yml is a file that contains a lists of roles that are automatically execute against hosts. Groups of hosts form your Ansible inventory, in our case in playbook.yml as you see below we have all the roles that need to be executed in order to install keycloak.
Mostly we don't change this, but if we don't want to add/delete a roles then we can adjust here
- hosts: all
roles:
- role: geerlingguy.java
become: yes
tags:
- java
- role: postgres
when: keycloak_db_type is defined and keycloak_db_type == "postgres"
tags:
- postgres
- role: nginx
tags:
- nginx
- role: keycloak
become: yes
tags:
- keycloak