[SOLVED] Can I use Jinja2 `map` filter in an Ansible play to get values from an array of objects?

Can I use Jinja2 `map` filter in an Ansible play to get values from an array of objects?

I have a playbook for creating some EC2 instances and then doing some stuff with them. The relevant pieces are approximately like:

- name: create ec2 instances
  ec2:
    id: '{{ item.name }}'
    instance_type: '{{ item.type }}'
  register: ec2
  with_items: '{{ my_instance_defs }}'
- name: wait for SSH
  wait_for:
    host: '{{ item.instances[0].private_ip }}'
    port: 22
  with_items: '{{ ec2.results }}'

This works as intended, but I am not especially happy with the item.instances[0].private_ip expression, partly because it shows really large objects in the play summary. I would love to have the with_items part just be an array of IP addresses, rather than an array of objects with arrays of objects inside them. In Python, I would just do something like:

ips = [r['instances'][0]['private_ip'] for r in ec2['results']]

And then I would use with_items: '{{ ips }}' in the second task.

Is there a way I can do the same thing using a J2 filter in the YAML of the play? Seems like http://docs.ansible.com/ansible/playbooks_filters.html#extracting-values-from-containers might be helpful, but I think that presupposes I have an array of keys/indices/whatever.

Solution

map filter is your friend here.

Something like this:

with_items: "{{ ec2.results | map(attribute='instances') | map('first') | map(attribute='private_ip') | list }}"

The code above is not tested.

You may want to try with debug first and gradually add additional map filters to get required result.

Don't forget to put | list at the end to make your map readable.