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Rebooting a host with Ansible

For a long time rebooting a host with Ansible has been tricky. The steps are:

  • ssh to the host
  • Reboot the host
  • Disconnect before the host closes your ssh connection
  • Wait some number of seconds to ensure the host has really shut down
  • Attempt to ssh to the host and execute a command
  • Repeat ssh attempt until it works or you give up

Seems clear enough, but if you Google for an answer you may end up at this StackExchange page that gives lots of not-quite-correct answers from 2015 (and one correct answer). Some people suggest checking port 22, but just because ssh is listening doesn’t mean that it’s at state where it’s accepting connections.

The correct answer is use Ansible version 2.7 or greater. 2.7 introduced the reboot command, and now all you have to do is add this to your list of handlers:

- name: Reboot host and wait for it to restart
  reboot:
    msg: "Reboot initiated by Ansible"
    connect_timeout: 5
    reboot_timeout: 600
    pre_reboot_delay: 0
    post_reboot_delay: 30
    test_command: whoami

This handler will:

  • Reboot the host
  • Wait 30 seconds
  • Attempt to connect via ssh and run whoami
  • Disconnect after 5 seconds if it ssh isn’t working
  • Keep attempting to connect for 10 minutes (600 seconds)

Add the directive:

  notify: Reboot host and wait for it to restart

… to any Ansible command that requires a reboot after a change. The host will be rebooted when the playbook finishes, then Ansible will wait until the host is back up and ssh is working before continuing on to the next playbook.

If you need to reboot halfway through a playbook you can force all handlers to execute with the command:

- name: Reboot if necessary
  meta: flush_handlers

I sometimes do that to change something, force a reboot, then verify that the change worked, all within the same playbook.

Hope you found this useful.

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