An Ansible MVP (Minimum Viable Playbook) for Testing Tasks

I showed this briefly in my post on merging groups and hostvars, but I thought it was worth writing a whole post on. The Minimum Viable Playbook (MVP) is the shortest, most useful Ansible playbook I have. Whenever I need to write some Ansible code and I’m not entirely sure I’m doing it right (which is often), I implement it first in the MVP so I can test it quickly. Here’s my latest iteration:

- hosts : localhost connection : local gather_facts : no vars : my_name : a_b_c tasks : - debug : msg={{ my_name|replace('_', '-') }}

I keep the MVP saved as ~/tmp/test.yml , from which it can be run with:

$ ansible-playbook -i localhost, ~/tmp/test.yml

(The -i argument allows you to specify the inventory as a comma-separated string of hosts, but it looks a little weird with only one host. You can’t leave out the comma, otherwise it gets interpreted as a filename.)

The MVP runs in about 0.2 seconds giving me quick feedback:

PLAY [ localhost] ************************************************************** TASK: [ debug ] **************************************************************** ok: [ localhost] => { "msg" : "a-b-c" } PLAY RECAP ******************************************************************** localhost : ok = 1 changed = 0 unreachable = 0 failed = 0

Here I was testing a rather trivial use of the replace filter, but since I wasn’t sure I remembered how it worked, it was faster to use the MVP than to test the full task I was writing, or to go to the documentation. Running the actual playbook would take minutes rather than seconds (even with --start-at-task , since it relied on other tasks), and while going to the documentation is normally fast (I use Dash for quick local look-ups), but it can be tricky when the answer might be split between the Ansible and Jinja 2 docs.

Two things make the MVP particularly fast:

When running tasks locally, Ansible always uses the local connection type, which means there is no SSH overhead. I’ve disabled fact-gathering which means my tasks are executed immediately. This saves about a second per run, which isn’t much but you do notice it.

Hope this helps you. If there’s something I’m missing, please let me know!

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Tags: ansible

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