Avoid the Changing Ansible Timestamp Gotcha
Submitted by Dale on October 1, 2020 - 1:17pm
Tagged:
Ansible variables are evaluated each time they're used. This means the following playbook vars declaration will always return the current time where ever it's used in the playbook!:
vars:
timestamp: "{{ lookup('pipe', 'date +%Y-%m-%d-%H%M') }}"This is not the desired situation if the timestamp is used as part of a filename. For example: filename: "backup-{{timestamp}}.sql".
Fortunately, there's an easy solution.
Host fact variables, created with set_fact module, are evaluated once and persistent. To create a timestamp that does not change:
- set_fact:
timestamp: "{{ lookup('pipe', 'date +%Y-%m-%d-%H%M') }}"The follow playbook demonstrates the difference between playbook variables and host fact variables:
- hosts: example.com
gather_facts: no
vars:
timestamp_var: "{{ lookup('pipe', 'date +%H:%M:%S') }}"
tasks:
- name: Set the playbook timestamp (so it doesn't change)
set_fact:
timestamp_host_fact: "{{ lookup('pipe', 'date +%H:%M:%S') }}"
- debug:
msg: "timestamp_var: {{ timestamp_var }} / timestamp_host_fact: {{ timestamp_host_fact }}"
- pause:
seconds: 3
- debug:
msg: "timestamp_var: {{ timestamp_var }} / timestamp_host_fact: {{ timestamp_host_fact }}"Playbook run:
