Ansible: Execute task only when a tag is specified

Solution 1:

Ansible 2.5 comes with special tags never and always. Tag never can be used exactly for this purpose. E.g:

tasks:
  - debug: msg='{{ showmevar}}'
    tags: [ 'never', 'debug' ]

In this example, the task will only run when the debug (or never) tag is explicitly requested. [Reference on ansible docs]

Solution 2:

Although this is a roundabout solution, it works.

Inside the task list register a variable when normal execution runs. Then, add a when condition that checks that variable to the tagged task.

- shell: /bin/true
  register: normal_task_list

- name: Only run when tag is specified
  shell: /bin/echo "Only running because of specified tag"
  when: normal_task_list is not defined
  tags: specified

Solution 3:

I don't have enough reputation to upvote or comment on the answer suggesting the use of command-line variables (--extra-vars), but I have this to add to it:

The caveat to this method is that the play will error and fail if you do not define that extra variable.

You can prevent play failure in the absence of an --extra-vars definition by defining a default value in the playbook itself:

---
- hosts: ...
# ↓↓↓
  vars:
    thorough: false
# ↑↑↑
  tasks:
  - name: apt - install nfs-common only when thorough is true
    when: thorough | bool
    apt:
      cache_valid_time: 86400
      force: yes
      pkg:
        - nfs-common

Overriding via --extra-vars will still work because variables defined on the command line take precedence over all other definitions.

The result is that the play runs without error when thorough is not changed to true on the command line.

Solution 4:

You can use Conditionals to protect against accidentally running tasks that would otherwise be executed if you don't specify a tag. The caveat to this method is that the play will error and fail if you do not define that extra variable.

Using the extra-vars argument you can trigger your conditional to be executed.

From ansible-playbook --help:

 -e EXTRA_VARS, --extra-vars=EXTRA_VARS
    set additional variables as key=value or YAML/JSON

Example:

ansible-playbook test.yaml -e "thorough=true"

test.yaml:

...
- name: apt - install nfs-common only when thorough is true
  apt:
    cache_valid_time: 86400
    force: yes
    pkg:
    - nfs-common
  when: thorough | default(False)
...

Solution 5:

Yes. Running ansible-playbook with the --tags foo flag will ensure that only tasks that are tagged with foo are executed. For example, assume we have a playbook called example.yml:

tasks:

  - yum: name={{ item }} state=installed
    with_items:
       - httpd
       - memcached
    tags:
       - packages

  - name: some other task
    ..
    tags:
      - some other tag

running:

ansible-playbook example.yml --tags "packages"

Will make sure only the yum task is executed.

So actually you don't really need to use tags in when section to conditionally execute a task. Notice that depending on the complexity of your playbooks/roles you might need to use a combination of --tags and --skip-tags to control which tasks are executed. For example, if an include tasks is tagged as 'foo' and some task inside the included playbook is tagged as 'bar' and you run 

ansible-playbook --tags "foo"

The internal task (tagged only as 'bar') will be executed. To avoid the execution of all internal tasks tagged as 'bar' you will have to execute the following command

ansible-playbook --tags foo --skip-tags bar

Tags:

Ansible

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