Ansible tuning

In this section we cover some options for tuning Ansible for performance and scale.

SSH pipelining

SSH pipelining is disabled in Ansible by default, but is generally safe to enable, and provides a reasonable performance improvement.

ansible.cfg
[ssh_connection]
pipelining = True

Forks

By default Ansible executes tasks using a fairly conservative 5 process forks. This limits the parallelism that allows Ansible to scale. Most Ansible control hosts will be able to handle far more forks than this. You will need to experiment to find out the CPU, memory and IO limits of your machine.

For example, to increase the number of forks to 20:

ansible.cfg
[defaults]
forks = 20

Fact caching

By default, Ansible gathers facts for each host at the beginning of every play, unless gather_facts is set to false. With a large number of hosts this can result in a significant amount of time spent gathering facts.

One way to improve this is through Ansible’s support for fact caching. In order to make this work with Kolla Ansible, it is necessary to change Ansible’s gathering configuration option to smart.

Example

In the following example we configure Kolla Ansible to use fact caching using the jsonfile cache plugin.

ansible.cfg
[defaults]
gathering = smart
fact_caching = jsonfile
fact_caching_connection = /tmp/ansible-facts

You may also wish to set the expiration timeout for the cache via [defaults] fact_caching_timeout.