+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 (currently only two steps are supported, but
+more may be added when required as additional services get converted to batched
+upgrades).
+
+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
+-------------
+
+Each service template may optionally define a `upgrade_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.
+
+ Steps/tages correlate to the following:
+
+ 1) Stop all control-plane services.
+
+ 2) Quiesce the control-plane, e.g disable LoadBalancer, stop
+ pacemaker cluster: this will stop the following resource:
+ - ocata:
+ - galera
+ - rabbit
+ - redis
+ - haproxy
+ - vips
+ - cinder-volumes
+ - cinder-backup
+ - manilla-share
+ - rbd-mirror
+
+ The exact order is controlled by the cluster constraints.
+
+ 3) Perform a package update and install new packages: A general
+ upgrade is done, and only new package should go into service
+ ansible tasks.
+
+ 4) Start services needed for migration tasks (e.g DB)
+
+ 5) Perform any migration tasks, e.g DB sync commands
+
+Note that the services are not started in the upgrade tasks - we instead re-run
+puppet which does any reconfiguration required for the new version, then starts
+the services.
+
+Nova Server Metadata Settings
+-----------------------------
+
+One can use the hook of type `OS::TripleO::ServiceServerMetadataHook` to pass
+entries to the nova instances' metadata. It is, however, disabled by default.
+In order to overwrite it one needs to define it in the resource registry. An
+implementation of this hook needs to conform to the following: