Ansible: Run task if server belongs to a group

Question

What's the sane way run a task only if the host belongs to one or more groups?

Currently, I'm using a boolean within the relevant group, e.g.:

Inventory file

[db_servers:vars]
copy_connection_string=true

-
  name: Copy db connection string file
  synchronize: src= ... (truncated for clarity)
  when: copy_connection_string is defined

What's the right condition in the when clause to check whether the current host belongs to the db_servers group?

Possible duplicate of [Run task only if host does not belong to a group](https://stackoverflow.com/questions/21008083/run-task-only-if-host-does-not-belong-to-a-group) — lingfish, Aug 23 '17 at 22:49
I wouldn't say so. That's a similar question but it's not the same question. — Jason Swett, Mar 23 '20 at 19:39

score 45 · Accepted Answer · edited Apr 27 '19 at 14:13

- name: Copy db connection string file
  synchronize:.........
  when: "'db_servers' in group_names"

The above Ansible task will only run if the host is a member of the db_servers group.