In some situations it may be helpful to populate the fact cache on
demand. The 'kolla-ansible gather-facts' command may be used to do this.

One specific case where this may be helpful is when running kolla-ansible
with a --limit argument, since in that case hosts that match the limit
will gather facts for hosts that fall outside the limit. In the extreme
case of a limit that matches only one host, it will serially gather
facts for all other hosts. To avoid this issue, run 'kolla-ansible
gather-facts' without a limit to populate the fact cache in parallel
before running the required command with a limit.

Change-Id: I79db9bca23aa1bd45bafa7e7500a90de5a684593

Ansible facts can have a large impact on the performance of the Ansible
control host. This patch introduces some control over which facts are
gathered (kolla_ansible_setup_gather_subset) and which facts are stored
(kolla_ansible_setup_filter). By default we do not change the default
values of these arguments to the setup module. The flexibility of these
arguments is limited, but they do provide enough for a large performance
improvement in a typical moderate to large OpenStack cloud.

In particular, the large complex dict fact for each interface has a
large effect, and on an OpenStack controller or hypervisor there may be
many virtual interfaces. We can use the kolla_ansible_setup_filter
variable to help:

    kolla_ansible_setup_filter: 'ansible_[!qt]*'

This causes Ansible to collect but not store facts matching that
pattern, which includes the virtual interface facts. Currently we are
not referencing other facts matching the pattern within Kolla Ansible.
Note that including the 'ansible_' prefix causes meta facts module_setup
and gather_subset to be filtered, but this seems to be the only way to
get a good match on the interface facts. To work around this, we use
ansible_facts rather than module_setup to detect whether facts exist in
the cache.

The exact improvement will vary, but has been reported to be as large as
18x on systems with many virtual interfaces.

For reference, here are some other tunings tried:

* Increased the number of forks (great speedup depending of the size of
  the deployment)
* Use `strategy = mitogen_linear` (cut processing time in half)
* Ansible caching (little speed up)
* SSH tunning (little speed up)

Co-Authored-By: Mark Goddard <mark@stackhpc.com>
Closes-Bug: #1921538
Change-Id: Iae8ca4aae945892f1dc65e1b10381d2e26e88805

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

Stolen from Kayobe.

Change-Id: I42a2ef84e5fe570e8001908614337e64d035ec99