Ansible

Ansible configuration is described in detail in the Ansible documentation. It is explained elsewhere in this guide how to configure Ansible for Kayobe and Kolla Ansible.

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.

$KAYOBE_CONFIG_PATH/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:

$KAYOBE_CONFIG_PATH/ansible.cfg
[defaults]
forks = 20

Fact caching

Note

Fact caching will not work correctly in Kayobe prior to the Ussuri release.

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 Kayobe, it is necessary to change Ansible’s gathering configuration option to smart. Additionally, it is necessary to use separate fact caches for Kayobe and Kolla Ansible due to some of the facts (e.g. ansible_user_uid and ansible_python) differing.

Example

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

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

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