Slow Ansible playbook? Check ansible.cfg!

Today while I was running a particularly large Ansible playbook about the 15th time in a row, I was wondering why this playbook seemed to run quite a bit slower than most other playbooks, even though I was managing a server that was in the same datacenter as most of my other infrastructure.

I have had pipelining = True in my system /etc/ansible/ansible.cfg for ages, and initially wondered why the individual tasks were so delayed—even when doing something like running three lineinfile tasks on one config file. The only major difference in this slow playbook's configuration was that I had a local ansible.cfg file in the playbook, to override my global roles_path (I wanted the specific role versions for this playbook to be managed and stored local to the playbook).

So, my curiosity led me to a more thorough reading of Ansible's configuration documentation, specifically a section talking about Ansible configuration file precedence:

Changes can be made and used in a configuration file which will be processed in the following order:

  • ANSIBLE_CONFIG (an environment variable)
  • ansible.cfg (in the current directory)
  • .ansible.cfg (in the home directory)
  • /etc/ansible/ansible.cfg

Ansible will process the above list and use the first file found. Settings in files are not merged.

Then it hit me—unlike vars_include and include module behavior within an Ansible playbook, Ansible configuration files (the ones that tell Ansible how to connect, how to optimize things over SSH, etc.) are not merged. Instead, Ansible uses the above hierarchy to choose one file, then it will use configuration overrides from that file and no others.

So even though I had the following in my global configuration file:

[ssh_connection]
pipelining = True
control_path = /tmp/ansible-ssh-%%h-%%p-%%r

The settings weren't applying to Ansible when I was running this large Ansible playbook, because it had its own ansible.cfg.

I copied and pasted my [ssh_connection] settings into the playbook's local ansible.cfg, and—well, the results speak for themselves:

Pipelining enabled Time to complete
No 03:28
Yes 01:42

So, two takeaways:

  • Unless it breaks your configuration, you should always set pipelining = True in ansible.cfg
  • If you add a custom ansible.cfg in a project/playbook, make sure you add in all the configuration you need—global overrides (e.g. in /etc/ansible/ansible.cfg) are not merged!

It looks like there's a related ticket that's been open for some time: Merge ansible config files, and even better—it looks like there's been some movement towards an implementation!