How can I run an Ansible block one host at a time?

Question

I have a playbook with something like this:

- name: Do this all one host at a time
  block:
    - name: Task A
      # do task A
    
    - name: Task B
      # do task B
  throttle: 1

I expect throttle: 1 to limit execution to one of the hosts at a time. It does this, but instead of running the whole block on host 1, then the whole block on host 2, etc. it runs Task A on host 1, Task A on host 2, Task B on host 1, Task B on host 2.

How can I run the entire block on each host in the group, one at a time?

(Note: there are other tasks in the playbook that should not run serially, hence not having the entire playbook run this way.)

Answer 1

You cannot do that on a block. What you are looking for is serial on a play. In a nutshell:

- name: Play those tasks serially
  hosts: my_group
  serial: 1

  tasks:
    - name: Task A
      # do task A
    
    - name: Task B
      # do task B