Correct way to use fail module and negative conditionals

Frank Ly

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Dec 19, 2015, 11:18:52 PM12/19/15

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I am trying to use the fail module at the very beginning of my playbook to check if the target server is a specific distribution and version. This way I can stop the playbook from running early on before any making any chances.

playbook:

---
- hosts: all

  tasks:
    - debug: msg='distro is {{ ansible_distribution }} and version is {{ ansible_distribution_major_version }}'

    - name: check if target server is CentOS 6
      fail: msg='You have attempted to run this playbook against an unsupported platform!'
      when: (ansible_distribution != "CentOS" and ansible_distribution_major_version != "6")

    - name: check if target server is CentOS 6 or Ubuntu 14
      fail: msg='unsupported platform detected!'
      when: (ansible_distribution != "CentOS" and ansible_distribution_major_version != "6") or (ansible_distribution != "Ubuntu" and ansible_distribution_major_version != "14")

    - debug: msg="Supported platform detected!"

playbook execution:


ansible-playbook test.yml -i inventory -u root -k
SSH password: 

PLAY [all] ******************************************************************** 

GATHERING FACTS *************************************************************** 
ok: [192.168.245.11]

TASK: [debug msg='distro is {{ ansible_distribution }} and version is {{ ansible_distribution_major_version }}'] *** 
ok: [192.168.245.11] => {
    "msg": "distro is CentOS and version is 6"
}

TASK: [check if target server is CentOS 6] *********************** 
skipping: [192.168.245.11]

TASK: [check if target server is CentOS 6 or Ubuntu 14] *********************** 
failed: [192.168.245.11] => {"failed": true}
msg: unsupported platform detected!

FATAL: all hosts have already failed -- aborting

PLAY RECAP ******************************************************************** 
           to retry, use: --limit @/tmp/test.retry

192.168.245.11               : ok=2    changed=0    unreachable=0    failed=1

Where am I going wrong ?

Frank Ly

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Dec 23, 2015, 4:44:35 PM12/23/15

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anyone able to help ?

Josh Smift

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Dec 23, 2015, 5:00:03 PM12/23/15

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FL> - name: check if target server is CentOS 6 or Ubuntu 14
FL> fail: msg='unsupported platform detected!'
FL> when: (ansible_distribution != "CentOS" and
FL> ansible_distribution_major_version != "6") or (ansible_distribution !=
FL> "Ubuntu" and ansible_distribution_major_version != "14")

This logic seems wrong to me. With

"msg": "distro is CentOS and version is 6"

then your when turns into

when: (False and False) or (True and True)

aka

when: False or True

aka True. Right?

I think you want something more like

when: NOT (CentOS 6 or Ubuntu 14)

than like

when: (not CentOS 6) or (not Ubuntu 14)

Because you're always going to be not one of those things -- you need to
negate the whole or.

-Josh (j...@care.com)

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Frank Ly

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Jan 5, 2016, 7:53:53 PM1/5/16

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Thanks for clarifying that for me Josh.

What I did was create a variable that contains the supported distributions and have my when condition check against it:

vars:
  supported_distros: "{{ ansible_distribution }} {{ ansible_distribution_major_version }}"

tasks:
  - name: check if server is running a supported distro
    fail: msg='Unsupported platform!'
    when: platform not in ["Ubuntu 14","CentOS 6"]