Blocks

Blocks create logical groups of tasks. Blocks also offer ways to handle task errors, similar to exception handling in many programming languages.

Grouping tasks with blocks
Handling errors with blocks

Grouping tasks with blocks

All tasks in a block inherit directives applied at the block level. Most of what you can apply to a single task (with the exception of loops) can be applied at the block level, so blocks make it much easier to set data or directives common to the tasks. The directive does not affect the block itself, it is only inherited by the tasks enclosed by a block. For example, a when statement is applied to the tasks within a block, not to the block itself.

Block example with named tasks inside the block

 tasks:
   - name: Install, configure, and start Apache
     when: ansible_facts['distribution'] == 'CentOS'
     block:
       - name: Install httpd and memcached
         ansible.builtin.yum:
           name:
           - httpd
           - memcached
           state: present

       - name: Apply the foo config template
         ansible.builtin.template:
           src: templates/src.j2
           dest: /etc/foo.conf

       - name: Start service bar and enable it
         ansible.builtin.service:
           name: bar
           state: started
           enabled: True
     become: true
     become_user: root
     ignore_errors: true

In the example above, the ‘when’ condition will be evaluated before Ansible runs each of the three tasks in the block. All three tasks also inherit the privilege escalation directives, running as the root user. Finally, ignore_errors: true ensures that Ansible continues to execute the playbook even if some of the tasks fail.

Note

All tasks in a block, including the ones included through include_role, inherit directives applied at the block level.

Names for blocks have been available since Ansible 2.3. We recommend using names in all tasks, within blocks or elsewhere, for better visibility into the tasks being executed when you run the playbook.

Handling errors with blocks

You can control how Ansible responds to task errors using blocks with rescue and always sections.

Rescue blocks specify tasks to run when an earlier task in a block fails. This approach is similar to exception handling in many programming languages. Ansible only runs rescue blocks after a task returns a ‘failed’ state. Bad task definitions and unreachable hosts will not trigger the rescue block.

Block error handling example

 tasks:
   - name: Handle the error
     block:
       - name: Print a message
         ansible.builtin.debug:
           msg: 'I execute normally'

       - name: Force a failure
         ansible.builtin.command: /bin/false

       - name: Never print this
         ansible.builtin.debug:
           msg: 'I never execute, due to the above task failing, :-('
     rescue:
       - name: Print when errors
         ansible.builtin.debug:
           msg: 'I caught an error, can do stuff here to fix it, :-)'

You can also add an always section to a block. Tasks in the always section run no matter what the task status of the previous block is.

Block with always section

 tasks:
   - name: Always do X
     block:
       - name: Print a message
         ansible.builtin.debug:
           msg: 'I execute normally'

       - name: Force a failure
         ansible.builtin.command: /bin/false

       - name: Never print this
         ansible.builtin.debug:
           msg: 'I never execute :-('
     always:
       - name: Always do this
         ansible.builtin.debug:
           msg: "This always executes, :-)"

Together, these elements offer complex error handling.

Block with all sections

 tasks:
   - name: Attempt and graceful roll back demo
     block:
       - name: Print a message
         ansible.builtin.debug:
           msg: 'I execute normally'

       - name: Force a failure
         ansible.builtin.command: /bin/false

       - name: Never print this
         ansible.builtin.debug:
           msg: 'I never execute, due to the above task failing, :-('
     rescue:
       - name: Print when errors
         ansible.builtin.debug:
           msg: 'I caught an error'

       - name: Force a failure in middle of recovery! >:-)
         ansible.builtin.command: /bin/false

       - name: Never print this
         ansible.builtin.debug:
           msg: 'I also never execute :-('
     always:
       - name: Always do this
         ansible.builtin.debug:
           msg: "This always executes"

The tasks in the block execute normally. If any tasks in the block return failed, the rescue section executes tasks to recover from the error. The always section runs regardless of the results of the block and rescue sections.

If an error occurs in the block and the rescue task succeeds, Ansible reverts the failed status of the original task for the run and continues to run the play as if the original task had succeeded. The rescued task is considered successful and does not trigger max_fail_percentage or any_errors_fatal configurations. However, Ansible still reports a failure in the playbook statistics.

You can use blocks with flush_handlers in a rescue task to ensure that all handlers run even if an error occurs:

Block run handlers in error handling

 tasks:
   - name: Attempt and graceful roll back demo
     block:
       - name: Print a message
         ansible.builtin.debug:
           msg: 'I execute normally'
         changed_when: true
         notify: Run me even after an error

       - name: Force a failure
         ansible.builtin.command: /bin/false
     rescue:
       - name: Make sure all handlers run
         meta: flush_handlers
 handlers:
    - name: Run me even after an error
      ansible.builtin.debug:
        msg: 'This handler runs even on error'

New in version 2.1.

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

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

These can be inspected in the rescue section:

Use special variables in rescue section.

 tasks:
   - name: Attempt and graceful roll back demo
     block:
       - name: Do Something
         ansible.builtin.shell: grep $(whoami) /etc/hosts

       - name: Force a failure, if previous one succeeds
         ansible.builtin.command: /bin/false
     rescue:
       - name: All is good if the first task failed
         when: ansible_failed_task.name == 'Do Something'
         ansible.builtin.debug:
           msg: All is good, ignore error as grep could not find 'me' in hosts

       - name: All is good if the second task failed
         when: "'/bin/false' in ansible_failed_result.cmd | d([])"
         ansible.builtin.fail:
           msg: It is still false!!!

Note

In ansible-core 2.14 or later, both variables are propagated from an inner block to an outer rescue portion of a block when nesting blocks.