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Asynchronous Actions and Polling

By default tasks in playbooks block, meaning the connections stay open until the task is done on each node. This may not always be desirable, or you may be running operations that take longer than the SSH timeout.

The easiest way to do this is to kick them off all at once and then poll until they are done.

You will also want to use asynchronous mode on very long running operations that might be subject to timeout.

To launch a task asynchronously, specify its maximum runtime and how frequently you would like to poll for status. The default poll value is 10 seconds if you do not specify a value for poll:

---

- hosts: all
  remote_user: root

  tasks:

  - name: simulate long running op (15 sec), wait for up to 45 sec, poll every 5 sec
    command: /bin/sleep 15
    async: 45
    poll: 5

Note

There is no default for the async time limit. If you leave off the ‘async’ keyword, the task runs synchronously, which is Ansible’s default.

Alternatively, if you do not need to wait on the task to complete, you may “fire and forget” by specifying a poll value of 0:

---

- hosts: all
  remote_user: root

  tasks:

  - name: simulate long running op, allow to run for 45 sec, fire and forget
    command: /bin/sleep 15
    async: 45
    poll: 0

Note

You shouldn’t “fire and forget” with operations that require exclusive locks, such as yum transactions, if you expect to run other commands later in the playbook against those same resources.

Note

Using a higher value for --forks will result in kicking off asynchronous tasks even faster. This also increases the efficiency of polling.

If you would like to perform a variation of the “fire and forget” where you “fire and forget, check on it later” you can perform a task similar to the following:

---
# Requires ansible 1.8+
- name: 'YUM - fire and forget task'
  yum: name=docker-io state=installed
  async: 1000
  poll: 0
  register: yum_sleeper

- name: 'YUM - check on fire and forget task'
  async_status: jid={{ yum_sleeper.ansible_job_id }}
  register: job_result
  until: job_result.finished
  retries: 30

Note

If the value of async: is not high enough, this will cause the “check on it later” task to fail because the temporary status file that the async_status: is looking for will not have been written or no longer exist

If you would like to run multiple asynchronous tasks while limiting the amount of tasks running concurrently, you can do it this way:

#####################
# main.yml
#####################
- name: Run items asynchronously in batch of two items
  vars:
    sleep_durations:
      - 1
      - 2
      - 3
      - 4
      - 5
    durations: "{{ item }}"
  include_tasks: execute_batch.yml
  with_items:
    - "{{ sleep_durations | batch(2) | list }}"

#####################
# execute_batch.yml
#####################
- name: Async sleeping for batched_items
  command: sleep {{ async_item }}
  async: 45
  poll: 0
  with_items: "{{ durations }}"
  loop_control:
    loop_var: "async_item"
  register: async_results

- name: Check sync status
  async_status:
    jid: "{{ async_result_item.ansible_job_id }}"
  with_items: "{{ async_results.results }}"
  loop_control:
    loop_var: "async_result_item"
  register: async_poll_results
  until: async_poll_results.finished
  retries: 30