How to run delegate_to task only on one host in group with if/when condition

Archives Ansible Project
1

Hi All,

My host file looks like below where I am using specific host variables “smca_role”.

[smca]
smca1 ansible_host=10.66.69.194 smca_role=True
smca2 ansible_host=10.66.69.193 smca_role=False

My playbook task looks like below. I am delegating a task to the above ‘smca’ group and it is going to run on both the hosts which I don’t want.

  • name: Check the flag for smca role
    shell: Some Command
    register: enable_result
    delegate_to: ‘{{ item }}’
    with_items: ‘{{ groups.smca }}’

My problem: I want to run it on only one host which matches the condition “smca_role=True”. How can I use jinja template & put if/when condition inside with_items: ‘{{ groups.smca }}’ so that it runs only on the required host ?

2

Try this.

`

  • name: Check the flag for smca role
    shell: Some Command
    register: enable_result
    delegate_to: ‘{{ groups.smca[0] }}’

`

The [0] gives you first member of the list.

To be honest if you are just doing tasks in a playbook I might just have a second play in the playbook to address the host I needed as I think it makes the playbook more readable.

`

  • hosts: smca
    tasks:

  • name: connect test
    wait_for_connection:

  • hosts: smca_lead_host
    tasks:

  • name: do a shell thing
    shell: echo Hello
    register: enable_result
    `

But it depends on what you are trying to achieve.

Hope this helps,

Jon

3

Hi Jon,

Thanks for your response. ‘{{ groups.smca[0] }}’ won’t work in my case as there is no guarantee that only the first host will have that condition true it can keep changing & smca group can have more than 2 hosts. The only thing unique would be one host will have **"**smca_role=True" and that’s the reason I want to check with that variable and then delegate. I guess there should be someway to specific conditions inside jinja template.

The separate playbook won’t work in what I am trying to achieve.

4

when: smca_role | bool

will give you that, only run on host where smca_role is True.

5

Hi Kai,

Thank You for the response. Using plain when condition won’t work in my case as the playbook is run on another host group where I’m gathering/setting facts and I’m using those facts when delegating it to “smca” host group.

My only requirement is to put this kind of when condition inside “with_items” so that it selects host which has "smca_role=True " and delegates the task only to that particular host.

6

And if you will try to separate main playbook to playbook + role?
Like that:

hosts:
[smca]
smca1 ansible_host=10.66.69.194
smca2 ansible_host=10.66.69.193

playbook.yml:

  • hosts: localhost
    roles:
  • { role: some_role, node: smca1, smca_role: True }
  • { role: some_role, node: smca2, smca_role: False }

some_role/tasks/main.yml

  • name: Check the flag for smca role
    shell: Some Command
    register: enable_result
    delegate_to: ‘{{ node }}’
    when: smca_role == “True”
7

If it isn’t working for you I suggest splitting it up and doing a set_fact to determine the host that has smca_role=True set. That way you can just delegate_to: the relevant host and don’t need to use ‘with_items’.

Hope this helps,

Jon