Fail instead of Warning when no hosts are matched - ansible

Question

when you don't have any hosts in inventory, when running playbook there is only warning:
[WARNING]: provided hosts list is empty, only localhost is available. Note that the implicit localhost does not match 'all'
Is there a way to make that Error instead of Warning?
I find out that there is this parameter in ansible.cfg:
[inventory]
unparsed_is_failed = True
but it will only return error when there is no inventory file which you are trying to use. It didn't look into content.

Answer 1

One simple solution is:
Create the playbook "main.yml" like:
---
# Check first if the supplied host pattern {{ RUNNER.HOSTNAME }} matches with the inventory
# or forces otherwise the playbook to fail (for Jenkins)
- hosts: localhost
vars_files:
- "{{ jsonfilename }}"
tasks:
- name: "Hostname validation | If OK, it will skip"
fail:
msg: "{{ RUNNER.HOSTNAME }} not found in the inventory group or hosts file {{ ansible_inventory_sources }}"
when: RUNNER.HOSTNAME not in hostvars
# The main playbook starts
- hosts: "{{ RUNNER.HOSTNAME }}"
vars_files:
- "{{ jsonfilename }}"
tasks:
- Your tasks
...
...
...
Put your host variables in a json file "var.json":
{
"RUNNER": {
"HOSTNAME": "hostname-to-check"
},
"VAR1":{
"CIAO": "CIAO"
}
}
Run the command:
ansible-playbook main.yml --extra-vars="jsonfilename=var.json"
You can also adapt this solution as you like and pass directly the hostname with the command
ansible-playbook -i hostname-to-check, my_playbook.yml
but in this last case remember to put in your playbook:
hosts: all

Answer 2

[WARNING]: provided hosts list is empty, only localhost is available. Note that the implicit localhost does not match 'all'
Q: "Is there a way to make that Error instead of Warning?"
A: Yes. It is. Test it in the playbook. For example,
- hosts: localhost
tasks:
- fail:
msg: "[ERROR] Empty inventory. No host available."
when: groups.all|length == 0
- hosts: all
tasks:
- debug:
msg: Playbook started
gives with an empty inventory
fatal: [localhost]: FAILED! => {"changed": false, "msg": "[ERROR] Empty inventory. No host available."}
Example of a project for testing
shell> tree .
.
├── ansible.cfg
├── hosts
└── pb.yml
0 directories, 3 files
shell> cat ansible.cfg
[defaults]
gathering = explicit
inventory = $PWD/hosts
shell> cat hosts
shell> cat pb.yml
- hosts: localhost
tasks:
- fail:
msg: "[ERROR] Empty inventory. No host available."
when: groups.all|length == 0
- hosts: all
tasks:
- debug:
msg: Playbook started
gives
shell> ansible-playbook pb.yml
[WARNING]: provided hosts list is empty, only localhost is available. Note that the implicit
localhost does not match 'all'
PLAY [localhost] *****************************************************************************
TASK [fail] **********************************************************************************
fatal: [localhost]: FAILED! => {"changed": false, "msg": "[ERROR] Empty inventory. No host available."}
PLAY RECAP ***********************************************************************************
localhost: ok=0 changed=0 unreachable=0 failed=1 skipped=0 rescued=0 ignored=0
Q: "Still I am getting a warning: [WARNING]: provided hosts list is empty, ..."
A: Feel free to turn the warning off. See LOCALHOST_WARNING.
shell> ANSIBLE_LOCALHOST_WARNING=false ansible-playbook pb.yml
PLAY [localhost] *****************************************************************************
TASK [fail] **********************************************************************************
fatal: [localhost]: FAILED! => {"changed": false, "msg": "[ERROR] Empty inventory. No host available."}
PLAY RECAP ***********************************************************************************
localhost: ok=0 changed=0 unreachable=0 failed=1 skipped=0 rescued=0 ignored=0