Making Ansible a Bit Faster2015-05-18
I recently reduced the YPlan build time by about 30% by tuning two Ansible settings. They’re not on by default, but work in most setups, so this will make a nice short guide on going faster.
The first thing to do before trying to find any performance improvements is always to gather some statistics! Googling “profile ansible” finds the Ansible Profiling plugin, which takes a mere three shell commands to install. There is also an accompanying blog post if you need more instruction. It gives you output like this at the end of a playbook run:
I added this and ran a build first so that I had a record of the baseline I had to improve upon.
1. SSH pipelining
SSH pipelining is an easy way of speeding up Ansible by “executing many ansible
modules without actual file transfer” (quote: [the docs]
(http://docs.ansible.com/intro_configuration.html#pipelining)). The boolean
flag defaults to off because some OS’s have a
/etc/sudoers config that
disallows it with
sudo with the
Fortunately the Ubuntu 14.04 EC2 base image that we use doesn’t even mention
requiretty, so I was fine to just add the setting to
This made things much snappier, especially for runs of small jobs such as
copying files with the
ControlPersist is an SSH feature that keeps the connection to the server open
as a socket, ready to reuse between invocations. With this on, Ansible can
avoid reconnecting to hosts for each task. Ansible actually has it on by
default, with the sockets stored in the directory indicated by
Unfortunately, as the docs indicate,
you can run into length problems when hostnames are quite long. Since we’re
using the EC2 DNS names like
ec2-123-123-123-123.eu-west-1.compute.amazonaws.com, I feared it might not be
working for us.
I found it hard to determine if ControlPersist was working from Ansible’s
output, even when using
-vvvv. Instead I watched the control path directory
on the Jenkins server whilst it ran a build with:
The ControlPersist sockets didn’t appear, indicating it wasn’t working. Sad face. Interpolating the full path for a control socket with the default settings, it would come to:
This is 102 characters, which is close to the suggested problem point of 108.
When I changed the setting to use
/tmp, it worked and I saw the sockets
This took a further 10-20% off the run time. Yay!
Further Speed Improvements
Since this, I’ve managed to make some more speed improvements by freezing some
configuration into a pre-built EC2 image, and using
async to parallelize
tasks - there’s a good blog post on this titled simply “Speed up your Ansible
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