Support Ansible max_fail_percentage

This allows us to continue execution until a certain proportion of hosts
to fail. This can be useful at scale, where failures are common, and
restarting a deployment is time-consuming.

The default max failure percentage is 100, keeping the default
behaviour. A global max failure percentage may be set via
kolla_max_fail_percentage, and individual services may define a max
failure percentage via <service>_max_fail_percentage.

Note that all hosts in the inventory must be reachable for fact
gathering, even those not included in a --limit.

Closes-Bug: #1833737
Change-Id: I808474a75c0f0e8b539dc0421374b06cea44be4f

1 files changed, 21 insertions, 0 deletions

diff --git a/doc/source/user/ansible-tuning.rst b/doc/source/user/ansible-tuning.rst
index 019dddedd..aa8db1cd2 100644
--- a/doc/source/user/ansible-tuning.rst
+++ b/doc/source/user/ansible-tuning.rst
@@ -139,3 +139,24 @@ facts via facter:
 .. code-block:: yaml
 
    kolla_ansible_setup_gather_subset: "all,!facter"
+
+Max failure percentage
+----------------------
+
+It is possible to specify a `maximum failure percentage
+<https://docs.ansible.com/ansible/latest/playbook_guide/playbooks_error_handling.html#setting-a-maximum-failure-percentage>`__
+using ``kolla_max_fail_percentage``. By default this is undefined, which is
+equivalent to a value of 100, meaning that Ansible will continue execution
+until all hosts have failed or completed. For example:
+
+.. code-block:: yaml
+
+   kolla_max_fail_percentage: 50
+
+A max fail percentage may be set for specific services using
+``<service>_max_fail_percentage``. For example:
+
+.. code-block:: yaml
+
+   kolla_max_fail_percentage: 50
+   nova_max_fail_percentage: 25