Add support for batched upgrades to composable upgrades

Some services (e.g ceph mon) require upgrading in batches (the old
upgrade architecture did the ceph mon upgrade one controller at a
time).  This interface enables doing the same, and over time we
can probably move more services into this interface (e.g when
services support rolling upgrades) to reduce downtime.

Change-Id: If581f301a5493ef33ac1386bdc22f9fca4f2544e
Partially-Implements: blueprint overcloud-upgrades-per-service

1 files changed, 22 insertions, 0 deletions

diff --git a/puppet/services/README.rst b/puppet/services/README.rst
index 6e4e9c1d..34cb350b 100644
--- a/puppet/services/README.rst
+++ b/puppet/services/README.rst
@@ -49,6 +49,28 @@ are re-asserted when applying latter ones.
 
    5) Service activation (Pacemaker)
 
+Batch Upgrade Steps
+-------------------
+
+Each service template may optionally define a `upgrade_batch_tasks` key, which
+is a list of ansible tasks to be performed during the upgrade process.
+
+Similar to the step_config, we allow a series of steps for the per-service
+upgrade sequence, defined as ansible tasks with a tag e.g "step1" for the first
+step, "step2" for the second, etc. Note that each step is performed in batches,
+then we move on to the next step which is also performed in batches (we don't
+perform all steps on one node, then move on to the next one which means you
+can sequence rolling upgrades of dependent services via the step value).
+
+The tasks performed at each step is service specific, but note that all batch
+upgrade steps are performed before the `upgrade_tasks` described below.  This
+means that all services that support rolling upgrades can be upgraded without
+downtime during `upgrade_batch_tasks`, then any remaining services are stopped
+and upgraded during `upgrade_tasks`
+
+The default batch size is 1, but this can be overridden for each role via the
+`upgrade_batch_size` option in roles_data.yaml
+
 Upgrade Steps
 -------------