Blocks

2024-07-08 15:25| 来源: 网络整理| 查看: 265

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

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 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 when: ansible_facts['distribution'] == 'CentOS' 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.

Blocks

Blocks

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