The When Statement

With the when clause, which contains a Jinja2 expression, It is easy to do something particular on a particular host:

  - name: "shutdown CentOS 6 and 7 system"
    command: /sbin/shutdown -t now
    when: ansible_distribution == "CentOS" and
          (ansible_distribution_major_version == "6" or ansible_distribution_major_version == "7")

A number of Jinja2 filters can be used in when statements.

Suppose we want to ignore the error of one statement and then decide to do something conditionaly based on success or failure:

  - command: /bin/false
    register: result
    ignore_errors: True

  - command: /bin/something
    when: result|failed
  - command: /bin/something_else
    when: result|success
  - command: /bin/still/something_else
    when: result|skipped

If you get some variable that’s a string and you’ll do a matn comparison on it:

  - shell: echo "only on RedHat 6, derivatives, and later"
    when: ansible_os_family == "RedHat" and ansible_lsb.major_release|int >= 6


The above example requires the lsb_release package on the target host in order to return the ansible_lsb.major_release fact.

  - command: echo {{item}}
    with_items: [1, 2, 3, 4, 5]
    when: item > 3

When combining when with with_items , be aware that the when statement is processed separately for each item.

Applying ‘When’ to roles and includes

Note that if you have several tasks that all share the same conditional statement, you can affix the conditional to a task include statement as below. Note this does not work with playbook includes, just task includes. All the tasks get evaluated, but the conditional is applied to each and every task:

- include: tasks/sometasks.yml
  when: ansible_os_family == "RedHat"

- hosts: webservers
    - { role: debian_stock_config, when: ansible_os_family == "Debian" }

Conditional Imports

Here is an example:

- hosts: all
  remote_user: root
    - "vars/common.yml"
    - [ "vars/{{ansible_os_family}}.yml", "vars/os_defaults.yml" ]

    - name: make sure apache is running
      service: name={{ apache }} state=running


Ansible’s approach to configuration - separating variables from tasks, keeps your playbooks from turning into arbitrary code with ugly nested ifs, conditionals, and so on - and results in more streamlines & auditable configuration rules - especially because there are a minimum of decision points to track.

Selecting Files and Templates Based On Variables

- name: template a file
  template: src={{item}} dest=/etc/apps/foo.conf
    - files:
        - {{ansible_os_family}}.conf
        - defaults.conf
        - search_path_one/somedir/
        - /opt/other/dir/


Sometimes a configuration file you want to copy, or a template you will use may depend on a variable. This example construct selects the first available file appropriate for the variables of a given host, which is often much cleaner than putting a lot of if conditionals in a template.

Register Variables

The register keyword decides what variable to save a result in. The resulting can be used in templates, action lines, or when statements.

- hosts: all
  remote_user: root
  gather_facts: true

    - name: register results
      command: cat /run/mysqld/
      register: result

    - name: result failed
      service: name=mysqld state=running
      when: result|failed

    - name: result success
      shell: cat /run/mysqld/ > /root/logfile
      when: result.stdout != ''

As result quite farmiliar with:

{u'changed': True, u'end': u'2015-06-10 12:51:43.636894', u'stdout': u'1351', u'cmd': [u'cat', u'/run/'], u'start': u'2015-06-10 12:51:43.630985', u'delta': u'0:00:00.005909', u'stderr': u'', u'rc': 0, 'invocation': {'module_name': 'command', 'module_args': 'cat /run/'}, 'stdout_lines': [u'1351']}

The registered result can be used in the with_item of a task if it is converted into a list as shown below:

  - name: get home dirs
    command: ls /home
    register: home_dirs

  - name: backup all home dirs
    file: path=/mnt/backup/{{item}} src=/home/{{item}} state=link
    with_items: home_dirs.stdout_lines
       # same as with_items: home_dirs.stdout.split()