Blocks¶
Blocks allow for logical grouping of tasks and in play error handling. Most of what you can apply to a single task (with the exception of loops) 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.
tasks:
- name: Install, configure, and start Apache
block:
- name: install httpd and memcached
yum:
name:
- httpd
- memcached
state: present
- name: apply the foo config template
template:
src: templates/src.j2
dest: /etc/foo.conf
- name: start service bar and enable it
service:
name: bar
state: started
enabled: True
when: ansible_facts['distribution'] == 'CentOS'
become: true
become_user: root
ignore_errors: yes
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. Finally, ignore_errors: yes
will continue executing the playbook even if some of the tasks fail.
Names for tasks within 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.
Blocks error handling¶
Blocks also introduce the ability to handle errors in a way similar to exceptions in most programming languages. Blocks only deal with ‘failed’ status of a task. A bad task definition or an unreachable host are not ‘rescuable’ errors.
tasks:
- name: Handle the error
block:
- debug:
msg: 'I execute normally'
- name: i force a failure
command: /bin/false
- debug:
msg: 'I never execute, due to the above task failing, :-('
rescue:
- debug:
msg: 'I caught an error, can do stuff here to fix it, :-)'
This will ‘revert’ the failed status of the task for the run and the play will continue as if it had succeeded.
There is also an always
section, that will run no matter what the task status is.
- name: Always do X
block:
- debug:
msg: 'I execute normally'
- name: i force a failure
command: /bin/false
- debug:
msg: 'I never execute :-('
always:
- debug:
msg: "This always executes, :-)"
They can be added all together to do complex error handling.
- name: Attempt and graceful roll back demo
block:
- debug:
msg: 'I execute normally'
- name: i force a failure
command: /bin/false
- debug:
msg: 'I never execute, due to the above task failing, :-('
rescue:
- debug:
msg: 'I caught an error'
- name: i force a failure in middle of recovery! >:-)
command: /bin/false
- debug:
msg: 'I also never execute :-('
always:
- 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 :
tasks:
- name: Attempt and graceful roll back demo
block:
- debug:
msg: 'I execute normally'
changed_when: yes
notify: run me even after an error
- command: /bin/false
rescue:
- name: make sure all handlers run
meta: flush_handlers
handlers:
- name: run me even after an error
debug:
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:
- 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.
See also
- About Playbooks
An introduction to playbooks
- Roles
Playbook organization by roles
- User Mailing List
Have a question? Stop by the google group!
- irc.freenode.net
#ansible IRC chat channel