Undefined variable when using lookup('dict', hostvars) or map('extract', hostvars)

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1

I’m trying to extract a few values from hostvars for subset of hosts, eg:

`

  • debug:
    msg:
  • “just a string” # a constant just to show the problem is not here
    loop: “{{ lookup(‘dict’, hostvars) }}”
    when: “item.key in groups[‘mygroup’]”
    `

or

`

  • debug:
    msg:
  • “just a string” # a constant just to show the problem is not here
    loop: “{{ groups[host_group] | map(‘extract’, hostvars) | list }}”
    `

when either of these run I get errors like

TASK [debug] *********************************************************************************************************************************************************************************************************************************** fatal: [localhost]: FAILED! => {"msg": "'ansible_memtotal_mb' is undefined"} to retry, use: --limit @/Users/bkaplan/.ansible/retry-files/ops-elk.retry

Where the undefined variable could be anything that might be in the huge set of variables for a host.

This seems to imply that lookup(‘dict’) and map(‘extract’) are trying to eagerly resolve the variables.

Is this expected? Why would these lookups so aggressively inspect the entire dict?

2

Here is what I did to get my results. Seems smelly but works.

`

  • debug:
    msg:
  • “{{ item }}”
    with_subelements:
  • “{{ groups[host_group] | map(‘extract’, hostvars) | dicts_pick([‘ec2_id’, ‘ansible_hostname’, ‘ansible_mounts’]) }}”
  • ‘ansible_mounts’
    `

with a custom filter

def dicts_pick(dicts, keys): results = [] for d in dicts: results.append({k: d[k] for k in keys}) return results