Serial execution of a role in Ansible

Question

I have a playbook defined as below:

- name: install percona rpms
  hosts: imdp
  roles:
    - role1
    - role2
    - role3
    - role4

I just want the tasks defined in role 3 to be executed serially. If I define serial: 1 in the role3 tasks, it doesn't work. All tasks are executed in parallel. But if I defined serial: 1 in the main yaml (the above yaml) then all the roles are executed serially, which is also not needed.

How can I get just role3 to be executed serially?

Answer 1

"serial" is available in a play only. See Playbook Keywords. The solution is to split the roles among more plays. For example

- name: Play 1. install percona rpms
  hosts: imdp
  roles:
    - role1
    - role2

- name: Play 2. install percona rpms
  hosts: imdp
  serial: 1
  roles:
    - role3

- name: Play 3. install percona rpms
  hosts: imdp
  roles:
    - role4