How to perform tasks only one host, based on previous output

[Kevin Csuka]

Hi,

My goal is to perform tasks only one host based on the output. Searched for --limit module to use in playbooks, but it is not present.

A shell script is executed on 3 nodes, which returns a boolean.

ok: [localMulti1] => {
    "variable": {
        ...
        "stdout": "true",
        ...
    }
}
ok: [localMulti2] => {
    "variable": {
        ...
        "stdout": "false",
        ...
    }
}
ok: [localMulti3] => {
    "variable": {
        ...
        "stdout": "false",
        ...
    }
}

How can I perform tasks on only on localMulti2? But not statically include the host (inventory_hostname == '...')

Failing with:

- shell: echo
  when: variable.stdout == "false" and ...

[Kevin Csuka]

No guru's who can reply?

[Brian Coca]

should be simple enough

- script: myscript

  register: myreturn

- command: othertask

  when: myreturn.stdout|bool 

​it will only execute 'othertask' on hosts in which the return is true.​

----------

Brian Coca

[Kevin Csuka]

Sorry if my message was unclear. The goal is to perform 'othertask' on only ONE host, where the value is false.

Your script will execute 'othertask' on ALL the hosts where the value is false, in this case, TWO hosts.

Also, run_once will not work because it will only run on the first host, where the boolean is true.

[Greg Langford]

Will the host be the same on each run?

If so you could put a guard round the task when ansible_inventory_hostname is equal to the desired host.

when: ansible_inventory_hostname == "desired-host-name"

Something like the above? Or maybe you could look into using delegated tasks http://docs.ansible.com/ansible/playbooks_delegation.html#delegation

Kind Regards

[Kevin Csuka]

Host differ each run. The task will be included in a role.

Is it possible to do something like:

when: variable.stdout == "false"

Register: myVar

Task: a task

Shell: echo

When: myVar is defined
Delegate_to: "{{ first-host-where_myVar is defined }}"

[Brian Coca]

Then just fail the 'true' host and now you can use run once with confidence only 'false' hosts got there.

- script: myscript

  register: myreturn

  failed_when: not myreturn.stdout|bool

- command: othertask

  run_once: true

----------

Brian Coca

[Kevin Csuka]

That task would still run on only the first host, and not the second.
Run_once will only perform the task on the first host... 

[Brian Coca]

Isn't that exactly what you wanted? if you want it to run on all 'false' hosts just remove the run_once

----------

Brian Coca

[Kevin Csuka]

Let met clarify. This is my output.

ok: [localMulti1] => {
    "variable": {
        ...
        "stdout": "true",
        ...
    }
}
ok: [localMulti2] => {
    "variable": {
        ...
        "stdout": "false",
        ...
    }
}
ok: [localMulti3] => {
    "variable": {
        ...
        "stdout": "false",
        ...
    }
}

How can I configure ansible to perform only a task on the second node, where the stdout is false. Not the third node
Run_once will never work, because it will always run it on the second host.

[Brian Coca]

>How can I configure ansible to perform only a task on the second node, where the stdout is false. Not the third node

> Run_once will never work, because it will always run it on the second host. 

you realize you are giving contradictory statements?

you want it to run on the 2nd, not the 3rd but run once will never work because it will run on the 2nd????

----------

Brian Coca

[Kevin Csuka]

Hihi, you're right. My bad, meant run_once will always run on the 1st node. 
Anyway...

[Brian Coca]

not in my example, as the first node is removed from the play.

----------

Brian Coca

[Kevin Csuka]

Nodes are excluded from a play when they fail. This is not the desired output.

I don't want to fail a task, I want it set-up as it should.

[Kevin Csuka]

Here is a playbook to test it locally.

---

- hosts: my-3-nodes

  tasks:

    - stat:

        path: /tmp/hi

      register: me

      

    - shell: echo

      when: me.stat.exists == true and ...

On node 2 and 3 perform:

$: touch /tmp/hi

[Brian Coca]

You keep changing the goalpost, now you want it to execute on every node? then  when: me.stat.exists == False is all you need.

----------

Brian Coca

[Kevin Csuka]

That would still perform it only on host 2 and 3.

Goal: perform task only one node 2 or 3 where the output is, in this case, true.

Thank you so much for your support :)

[Brian Coca]

Then my first suggestion works for that case.

----------

Brian Coca

[Kevin Csuka]

Not what I desire, because it will perform the task on both 2 and 3.
I only desire to perform a task on 2 OR 3.

[Brian Coca]

run_once prevents that

----------

Brian Coca

[Kevin Csuka]

No it does not. run_once will only perform a task on node1, therefor skip the task.
Please re-check in a local environment.

[Brian Coca]

last time i explain this:

- script: myscript

  register: myreturn

  failed_when: not myreturn.stdout|bool

# ^ this will remove host 1 from the host list so the next task only chooses 'first host' from 2 and 3

- command: othertask

  run_once: true

# ^ this task runs against ONLY 2 OR 3

----------

Brian Coca

[Kai Stian Olstad]

- set_fact:
run_on: "{{ item }}"
with_items: "{{ play_hosts }}"
when: run_on is undefined and hostvars[item].me.stat.exists
run_once: true

- shell: echo
when: inventory_hostname == run_on


--
Kai Stian Olstad

[Kevin Csuka]

This will FAIL the task at node 1, which is in no way desired. That is no real solution.

Also, after 'othertask' has been run, I'd like to perform other tasks on node 1.

[Kevin Csuka]

Hallelujah! You did it. Big thanks to you sir!

TASK [command] *****************************************************************

Saturday 17 December 2016  14:08:12 +0100 (0:00:00.101)       0:00:01.122 *****

skipping: [localMulti1]

skipping: [localMulti3]

changed: [localMulti2]

PLAY RECAP *********************************************************************

localMulti1                : ok=3    changed=0    unreachable=0    failed=0

localMulti2                : ok=3    changed=1    unreachable=0    failed=0

localMulti3                : ok=2    changed=0    unreachable=0    failed=0

[Arbab Nazar]

Kevin, can you please show the playbook/tasks that are working for you so that it will help others. Thanks

[Kevin Csuka]

Erhm, the solution is in the quoted text..
Here is a copy/paste: