How to Skip Ansible Host if member of a group

Question

I am working on a playbook (for use in AWX) to handle some backend processing for one of our web apps. One of the extra variables passed to the playbook via a REST call to AWX is used to pass the hosts
to the playbook

hosts: {{target}}

target can be a single server or a list of servers.
Question: how can I use patterns to skip a host if it is not a member of an inventory group
e.g if I want the playbook to skip a server if it's in the staging group in inventory
I have tried the following:

hosts: "{{target}}:!staging"

this only works if only one server is sent as target var, however it fails if called with a list.

Answer 1

This should work if you do use : as delimiter for your hosts and not ,.

---

The syntax host1:host2:host3:!staging works, but host1,host2,host3:!staging, on the other hand, does generates a warning

[WARNING]: Could not match supplied host pattern, ignoring: host3:!staging

and this could well be the issue you are facing too.
^{The two syntaxes are documented here}

Given the inventory:

all:
  hosts:
    host1:
    host2:
    host3:

  children:
    staging:
      hosts:
        host2:

And the playbook:

- hosts: host1:host2:host3:!staging
  gather_facts: no
      
  tasks:
    - debug:
        msg: "{{ inventory_hostname  }}"

This yields the recap:

PLAY [host1:host2:host3:!staging] *********************************************************************************

TASK [debug] ******************************************************************************************************
ok: [host1] => {
    "msg": "host1"
}
ok: [host3] => {
    "msg": "host3"
}

PLAY RECAP ********************************************************************************************************
host1                      : ok=1    changed=0    unreachable=0    failed=0    skipped=0    rescued=0    ignored=0   
host3                      : ok=1    changed=0    unreachable=0    failed=0    skipped=0    rescued=0    ignored=0   

---

And it gives the exact same recap when using the playbook:

- hosts: "{{ target }}:!staging"
  gather_facts: no
      
  tasks:
    - debug:
        msg: "{{ inventory_hostname  }}"

Run via:

ansible-playbook play.yml -i inventory.yml -e "target=host1:host2:host3"