Mark Goddard ade5bfa302 Use ansible_facts to reference facts

By default, Ansible injects a variable for every fact, prefixed with
ansible_. This can result in a large number of variables for each host,
which at scale can incur a performance penalty. Ansible provides a
configuration option [0] that can be set to False to prevent this
injection of facts. In this case, facts should be referenced via
ansible_facts.<fact>.

This change updates all references to Ansible facts within Kolla Ansible
from using individual fact variables to using the items in the
ansible_facts dictionary. This allows users to disable fact variable
injection in their Ansible configuration, which may provide some
performance improvement.

This change disables fact variable injection in the ansible
configuration used in CI, to catch any attempts to use the injected
variables.

[0] https://docs.ansible.com/ansible/latest/reference_appendices/config.html#inject-facts-as-vars

Change-Id: I7e9d5c9b8b9164d4aee3abb4e37c8f28d98ff5d1
Partially-Implements: blueprint performance-improvements

2021-06-23 10:38:06 +01:00

2.6 KiB

Raw Blame History

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.

[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:

[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.

[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.

Fact variable injection

By default, Ansible injects a variable for every fact, prefixed with ansible_. This can result in a large number of variables for each host, which at scale can incur a performance penalty. Ansible provides a configuration option that can be set to False to prevent this injection of facts. In this case, facts should be referenced via ansible_facts.<fact>. In recent releases of Kolla Ansible, facts are referenced via ansible_facts, allowing users to disable fact variable injection.

[defaults]
inject_facts_as_vars = False

2.6 KiB Raw Blame History