Ansible serial task(s) hack - https://github.com/ansible/ansible/issues/83227#issuecomment-2122724780

0playbook.yml

- name: output
  hosts: k8s_cluster
  tasks:
  - name: Rolling (intended behavior)
    ansible.builtin.include_tasks: change_config.yml
    with_items: "{{ groups['k8s_cluster'] }}"
    loop_control:
      loop_var: _host_item
    when:
      - hostvars[_host_item].inventory_hostname == inventory_hostname

  - name: Rolling (doesn't work)
    ansible.builtin.include_tasks: change_config.yml
    when:
    - ('k8s_cluster' in groups)
    vars:
      _host_item: '{{inventory_hostname}}'

change_config.yml

- debug:
    msg: "Starting {{ inventory_hostname }}"
- wait_for:
    timeout: 1
  delegate_to: localhost
- debug:
    msg: "Ending {{ inventory_hostname }}"

inventory.yml

k8s_cluster:
  children:
    servers:
      hosts:
        server-0:
        server-1:
        server-2:
    agents:
      hosts:
        agent-0:
        agent-1:
        agent-2:

output.txt

PLAY [output] ****************************************************************************************************************

TASK [Rolling (intended behavior)] *******************************************************************************************
skipping: [server-0] => (item=server-1) 
skipping: [server-1] => (item=server-0) 
skipping: [server-0] => (item=server-2) 
skipping: [server-0] => (item=agent-0) 
skipping: [server-2] => (item=server-0) 
skipping: [server-1] => (item=server-2) 
skipping: [server-0] => (item=agent-1) 
skipping: [server-2] => (item=server-1) 
skipping: [server-1] => (item=agent-0) 
skipping: [server-0] => (item=agent-2) 
skipping: [agent-0] => (item=server-0) 
skipping: [server-1] => (item=agent-1) 
skipping: [server-2] => (item=agent-0) 
skipping: [agent-0] => (item=server-1) 
skipping: [server-1] => (item=agent-2) 
skipping: [agent-0] => (item=server-2) 
skipping: [server-2] => (item=agent-1) 
skipping: [server-2] => (item=agent-2) 
skipping: [agent-1] => (item=server-0) 
skipping: [agent-0] => (item=agent-1) 
skipping: [agent-1] => (item=server-1) 
skipping: [agent-0] => (item=agent-2) 
skipping: [agent-1] => (item=server-2) 
skipping: [agent-2] => (item=server-0) 
skipping: [agent-1] => (item=agent-0) 
skipping: [agent-2] => (item=server-1) 
skipping: [agent-1] => (item=agent-2) 
skipping: [agent-2] => (item=server-2) 
skipping: [agent-2] => (item=agent-0) 
skipping: [agent-2] => (item=agent-1) 
included: /Users/gpratt/Code/CNS/app-platform/tests/integration/targets/lookup_phased_rollout/playbooks/default/change_config.yml for server-0 => (item=server-0)
included: /Users/gpratt/Code/CNS/app-platform/tests/integration/targets/lookup_phased_rollout/playbooks/default/change_config.yml for server-1 => (item=server-1)
included: /Users/gpratt/Code/CNS/app-platform/tests/integration/targets/lookup_phased_rollout/playbooks/default/change_config.yml for server-2 => (item=server-2)
included: /Users/gpratt/Code/CNS/app-platform/tests/integration/targets/lookup_phased_rollout/playbooks/default/change_config.yml for agent-0 => (item=agent-0)
included: /Users/gpratt/Code/CNS/app-platform/tests/integration/targets/lookup_phased_rollout/playbooks/default/change_config.yml for agent-1 => (item=agent-1)
included: /Users/gpratt/Code/CNS/app-platform/tests/integration/targets/lookup_phased_rollout/playbooks/default/change_config.yml for agent-2 => (item=agent-2)

TASK [debug] *****************************************************************************************************************
ok: [server-0] => {
    "msg": "Starting server-0"
}

TASK [wait_for] **************************************************************************************************************
ok: [server-0 -> localhost]

TASK [debug] *****************************************************************************************************************
ok: [server-0] => {
    "msg": "Ending server-0"
}

TASK [debug] *****************************************************************************************************************
ok: [server-1] => {
    "msg": "Starting server-1"
}

TASK [wait_for] **************************************************************************************************************
ok: [server-1 -> localhost]

TASK [debug] *****************************************************************************************************************
ok: [server-1] => {
    "msg": "Ending server-1"
}

TASK [debug] *****************************************************************************************************************
ok: [server-2] => {
    "msg": "Starting server-2"
}

TASK [wait_for] **************************************************************************************************************
ok: [server-2 -> localhost]

TASK [debug] *****************************************************************************************************************
ok: [server-2] => {
    "msg": "Ending server-2"
}

TASK [debug] *****************************************************************************************************************
ok: [agent-0] => {
    "msg": "Starting agent-0"
}

TASK [wait_for] **************************************************************************************************************
ok: [agent-0 -> localhost]

TASK [debug] *****************************************************************************************************************
ok: [agent-0] => {
    "msg": "Ending agent-0"
}

TASK [debug] *****************************************************************************************************************
ok: [agent-1] => {
    "msg": "Starting agent-1"
}

TASK [wait_for] **************************************************************************************************************
ok: [agent-1 -> localhost]

TASK [debug] *****************************************************************************************************************
ok: [agent-1] => {
    "msg": "Ending agent-1"
}

TASK [debug] *****************************************************************************************************************
ok: [agent-2] => {
    "msg": "Starting agent-2"
}

TASK [wait_for] **************************************************************************************************************
ok: [agent-2 -> localhost]

TASK [debug] *****************************************************************************************************************
ok: [agent-2] => {
    "msg": "Ending agent-2"
}

TASK [Rolling (doesn't work)] ************************************************************************************************
included: /Users/gpratt/Code/CNS/app-platform/tests/integration/targets/lookup_phased_rollout/playbooks/default/change_config.yml for server-0, server-1, server-2, agent-0, agent-1, agent-2

TASK [debug] *****************************************************************************************************************
ok: [server-0] => {
    "msg": "Starting server-0"
}
ok: [server-1] => {
    "msg": "Starting server-1"
}
ok: [server-2] => {
    "msg": "Starting server-2"
}
ok: [agent-0] => {
    "msg": "Starting agent-0"
}
ok: [agent-1] => {
    "msg": "Starting agent-1"
}
ok: [agent-2] => {
    "msg": "Starting agent-2"
}

TASK [wait_for] **************************************************************************************************************
ok: [server-0 -> localhost]
ok: [agent-0 -> localhost]
ok: [agent-1 -> localhost]
ok: [server-2 -> localhost]
ok: [server-1 -> localhost]
ok: [agent-2 -> localhost]

TASK [debug] *****************************************************************************************************************
ok: [server-0] => {
    "msg": "Ending server-0"
}
ok: [server-1] => {
    "msg": "Ending server-1"
}
ok: [server-2] => {
    "msg": "Ending server-2"
}
ok: [agent-0] => {
    "msg": "Ending agent-0"
}
ok: [agent-1] => {
    "msg": "Ending agent-1"
}
ok: [agent-2] => {
    "msg": "Ending agent-2"
}

PLAY RECAP *******************************************************************************************************************
agent-0                    : ok=8    changed=0    unreachable=0    failed=0    skipped=0    rescued=0    ignored=0   
agent-1                    : ok=8    changed=0    unreachable=0    failed=0    skipped=0    rescued=0    ignored=0   
agent-2                    : ok=8    changed=0    unreachable=0    failed=0    skipped=0    rescued=0    ignored=0   
server-0                   : ok=8    changed=0    unreachable=0    failed=0    skipped=0    rescued=0    ignored=0   
server-1                   : ok=8    changed=0    unreachable=0    failed=0    skipped=0    rescued=0    ignored=0   
server-2                   : ok=8    changed=0    unreachable=0    failed=0    skipped=0    rescued=0    ignored=0