How to conditionally check the state of an openstack instance

Question

I am trying to conditionally check the state of an openstack cloud instance in my playbook.

The playbook takes the name of a cloud instance as a parameter and then deletes it by setting the state to absent using nova compute. What I want to do is check if the state is already absent (say the name of a non-existent instance has been entered) to skip the statement. How would I write that?

- nova_compute
     name: "{{item}}"
     state: absent
  with_items: "{{instance_name}}"
  when: ???

Answer 1

I'm not familiar with the openstack tasks, but it looks like this shouldn't be terribly difficult to do. First off, if all you want to do is terminate all your instances and you're getting an error because some already don't exist then simply ignoring errors might suffice:

- nova_compute
     name: "{{item}}"
     state: absent
  with_items: "{{instance_name}}"
  ignore_errors: yes

If you don't want to do that then you'd need to split this out into multiple tasks, one to check the state of the instance(s) and another one to terminate them.

The Ansible documentation looks like it's recently been updated for Ansible 2.0, so I'm not sure if the module names have changed sufficiently or not, but given what's currently documented I'd suggest using a task to gather facts for the instance in question. If the task returns an error then the instance doesn't exist, which is what you're really after, so something like this should work:

- os_server_facts
      name: "{{instance_name}}"
      register: instance_state
      ignore_errors: yes

And then you can do something like this:

- nova_compute
      name: "{{instance_name}}"
      state: absent
      when: instance_state is not defined 

Depending on what the first task returns for instance_state you might want the when clause to be a bit more structured. I'd suggest running a few tests and outputting instance_state via the debug module to see if you need to do anything beyond what I provided here.

If you need to do this with a list of instances you should be able to expand the tasks a bit to do that as well. Something along these lines (obviously I haven't actually tested these so they may not be 100% correct):

- os_server_facts
      name: "{{item}}"
      register: instance_state
      ignore_errors: yes
      with_items: "{{instance_list}}"

- nova_compute
      name: "{{item}}"
      state: absent
      when: instance_state[item] is not defined 
      with_items: "{{instance_list}}"