How to terminate an Ansible playbook run when it is successful on one host?

Question

I have a system with several hosts for availability. I only need to run my Ansible playbook on one host. However some of these hosts may not be reachable. Let's say I have host1, host2, host3 ... If host1 is not reachable, I want Ansible to try host2. If host2 is reachable and Ansible runs some bash scripts successfully, I want Ansible to skip the rest of hosts. Any suggestions?

How do you define "some" in "runs some bash scripts successfully"? — techraf
And how do you define "unreachable"? Ansible automatically skips hosts unreachable by ssh. — sm4rk0
@sm4rk0 I'm curious how would it influence the answer? The only determinant whether to continue trying or to stop is a successful execution (of mysterious "some" scripts). What role does the definition of "unreachable" play for the answer, in your opinion? — techraf

sm4rk0 sm4rk0 · Accepted Answer · 2017-02-22T11:58:42

This is probably not the optimal solution, but I couldn't find a better one.

(Optionally) Set gather_facts to False, to entirely skip the hosts that need to be skipped (if you don't need to gather the host facts).
Set serial to 1, so the playbook is played entirely on one host at a time instead of the default 5 hosts in parallel.
Use set_fact to set a host fact (named done in example) to True at the end of a play, or use register if you need a more specific condition (a command output).
Use end_play meta at the start of the play that would execute when the variable is set to True (or has the expected value, if you used register) for any host. I used the Jinja2 template language to extract the value this way:
1. for to loop over all the hostvars (Python dict containing all the variables set for all hosts in the inventory).
2. if to check whether a host has done variable set to True and return a string True if it is.
3. default filter to set the default value if done is not defined for a host (that would cause an error 'dict object' has no attribute 'done').

For example:

- hosts: all
  serial: 1
  gather_facts: False

  tasks:
  - meta: end_play
    when: "{% for item in hostvars.values() %}{% if item.done|default(False) %}True{% endif %}{% endfor %}"

  # The rest of the play goes here

  - set_fact:
      done: True

How to terminate an Ansible playbook run when it is successful on one host?

2 Answers