Minimizing Conditionals in Ansible

2017-08-25

Ansible gives you conditionals to use when you want to check if something meets a certain criteria. However conditionals can become annoying if you need many include statements or repeat tasks based on facts. Here’s a way to minimize the need for them in the tasks themselves.

Let’s take Apache for example:


- name: install apache
  package:
    name: httpd
    state: installed
  when: ansible_distribution == 'CentOS'
- name: install apache
  package:
    name: apache2
    state: installed
  when: ansible_distribution == 'Ubuntu'


- name: install apache
  package:
    name: httpd
    state: installed
  when: ansible_distribution == 'CentOS'
- name: install apache
  package:
    name: apache2
    state: installed
  when: ansible_distribution == 'Ubuntu'

This can become annoying and hard to read when it’s all in one file. If you have a lot of these you can separate out specific .yml files to include a conditional:


- include: centos.yml
  when: ansible_distribution == 'CentOS'
- include: ubuntu.yml
  when: ansible_distribution == 'Ubuntu'


- include: centos.yml
  when: ansible_distribution == 'CentOS'
- include: ubuntu.yml
  when: ansible_distribution == 'Ubuntu'

However sometimes a cleaner way (in my opinion) is to use a variable to minimize the use of conditional statements. Using the same example with Apache:


- name: install apache
  package:
    name: "{{ apache_package }}"
    state: installed


- name: install apache
  package:
    name: "{{ apache_package }}"
    state: installed

Then in your variables file set this dictionary and variable:


dist_dict:
  "RedHat":
    apache: 'httpd'
  "Fedora":
    apache: 'httpd'
  "CentOS":
    apache: 'httpd'
  "Ubunu":
    apache: 'apache2'
apache_package: "{{ dist_dict[ansible_distribution]['apache'] }}"


dist_dict:
  "RedHat":
    apache: 'httpd'
  "Fedora":
    apache: 'httpd'
  "CentOS":
    apache: 'httpd'
  "Ubunu":
    apache: 'apache2'
apache_package: "{{ dist_dict[ansible_distribution]['apache'] }}"

You can take this one step further and utilize that same dictionary for services (and other things) as well.


dist_dict:
  "RedHat":
    apache_package: 'httpd'
    apache_service: 'httpd'
  "Fedora":
    apache_package: 'httpd'
    apache_service: 'httpd'
  "CentOS":
    apache_package: 'httpd'
    apache_service: 'httpd'
  "Ubunu":
    apache_package: 'apache2'
    apache_service: 'apache2'
apache_package: "{{ dist_dict[ansible_distribution]['apache_package'] }}"
apache_service: "{{ dist_dict[ansible_distribution]['service_service'] }}"


dist_dict:
  "RedHat":
    apache_package: 'httpd'
    apache_service: 'httpd'
  "Fedora":
    apache_package: 'httpd'
    apache_service: 'httpd'
  "CentOS":
    apache_package: 'httpd'
    apache_service: 'httpd'
  "Ubunu":
    apache_package: 'apache2'
    apache_service: 'apache2'
apache_package: "{{ dist_dict[ansible_distribution]['apache_package'] }}"
apache_service: "{{ dist_dict[ansible_distribution]['service_service'] }}"

Then your tasks could simply be:


- name: install apache
  package:
    name: "{{ apache_package }}"
    state: installed
- name: start apache
  service:
    name: "{{ apache_service }}"
    state: started
    enabled: true


- name: install apache
  package:
    name: "{{ apache_package }}"
    state: installed
- name: start apache
  service:
    name: "{{ apache_service }}"
    state: started
    enabled: true

This gives you the power to utilize these variables in other places without including whole .yml files or using a bunch of conditional statements.