Ansible command module expecting nonzero result - ansible

Question

I am trying to use the Ansible command module to get information from my inventory, but I am expecting the servers to return a non-zero value as a result. The non-zero values are causing the inventory to report as fail.
I was expecting the following sequence to fail when a certain group of process names are present on any of the inventory.
- name: Make sure all expected processes are down
tags: ensure_processes_down
block:
- name: Find list of unexpected processes
command:
argv:
- /usr/bin/pgrep
- --list-name
- unexpected_processes_pattern_here
register: pgrep_status
- name: Ensure no processes were found
# pgrep returns 0 if matches were found
assert:
that: pgrep_status.rc != 0
msg: 'Cannot run while these these processes are up: {{ pgrep_status.stdout }}'
I am new to Ansible and suspect that I am not using the command module correctly.
Is there another way to run a command where the expected return code is non-zero?

Answer 1

If the command in a command task fails, then the entire task fails, which means no more tasks will be executed on that particular host. Your second task in which you check pgrep_status will never run. You have a couple options here.
You can set ignore_errors: true, which will ignore the error condition and move on to the next task. E.g:
- hosts: localhost
gather_facts: false
tasks:
- command:
argv:
- false
register: status
ignore_errors: true
- assert:
that: status.rc != 0
Which will produce this result:
PLAY [localhost] ***************************************************************
TASK [command] *****************************************************************
fatal: [localhost]: FAILED! => {"changed": false, "cmd": "False", "msg": "[Errno 2] No such file or directory: b'False'", "rc": 2, "stderr": "", "stderr_lines": [], "stdout": "", "stdout_lines": []}
...ignoring
TASK [assert] ******************************************************************
ok: [localhost] => {
"changed": false,
"msg": "All assertions passed"
}
PLAY RECAP *********************************************************************
localhost : ok=2 changed=0 unreachable=0 failed=0 skipped=0 rescued=0 ignored=1
However, rather than running the command task and then checking the result in a second task, you can set a failed_when condition on the command task:
- name: Find list of unexpected processes
command:
argv:
- /usr/bin/pgrep
- --list-name
- unexpected_processes_pattern_here
register: pgrep_status
failed_when: pgrep_status.rc == 0
This command will only fail when the command returns successfully (i.e.,with an exit code of 0).
See the "Defining failure" section of the docs for more information.