Blocks allow for logical grouping of tasks and in play error handling. Most of what you can apply to a single task can be applied at the block level, which also makes it much easier to set data or directives common to the tasks. This does not mean the directive affects the block itself, but is inherited by the tasks enclosed by a block. i.e. a when will be applied to the tasks, not the block itself.

Block example
   - name: Install Apache
       - yum:
           name: "{{ item }}"
           state: installed
           - httpd
           - memcached
       - template:
           src: templates/src.j2
           dest: /etc/foo.conf
       - service:
           name: bar
           state: started
           enabled: True
     when: ansible_distribution == 'CentOS'
     become: true
     become_user: root

In the example above, each of the 3 tasks will be executed after appending the when condition from the block and evaluating it in the task’s context. Also they inherit the privilege escalation directives enabling “become to root” for all the enclosed tasks.

New in version 2.3: The name: keyword for block: was added in Ansible 2.3.

Error Handling

Blocks also introduce the ability to handle errors in a way similar to exceptions in most programming languages.

Block error handling example
 - name: Attempt and graceful roll back demo
     - debug:
         msg: 'I execute normally'
     - command: /bin/false
     - debug:
         msg: 'I never execute, due to the above task failing'
     - debug:
         msg: 'I caught an error'
     - command: /bin/false
     - debug:
         msg: 'I also never execute :-('
     - debug:
         msg: "This always executes"

The tasks in the block would execute normally, if there is any error the rescue section would get executed with whatever you need to do to recover from the previous error. The always section runs no matter what previous error did or did not occur in the block and rescue sections. It should be noted that the play continues if a rescue section completes successfully as it ‘erases’ the error status (but not the reporting), this means it won’t trigger max_fail_percentage nor any_errors_fatal configurations but will appear in the playbook statistics.

Another example is how to run handlers after an error occurred :

Block run handlers in error handling
   - name: Attempt and graceful roll back demo
       - debug:
           msg: 'I execute normally'
         notify: run me even after an error
       - command: /bin/false
       - name: make sure all handlers run
         meta: flush_handlers
    - name: run me even after an error
        msg: 'This handler runs even on error'

New in version 2.1.

Ansible also provides a couple of variables for tasks in the rescue portion of a block:

The task that returned ‘failed’ and triggered the rescue. For example, to get the name use
The captured return result of the failed task that triggered the rescue. This would equate to having used this var in the register keyword.

See also

Working With Playbooks
An introduction to playbooks
Playbook organization by roles
User Mailing List
Have a question? Stop by the google group!
#ansible IRC chat channel