Document upgrading for operators

This documents the basics of upgrades.

Partially implements: blueprint documentation-rework
Change-Id: I042179aec0e4a43b82f5ccaf6262217301ae46c6

doc/operating-kolla.rst

@@ -6,7 +6,62 @@ Operating Kolla
 
 Upgrading
 =========
-TODO(all) fill this section out
+Kolla's strategy for upgrades is to never make a mess and follow consistent
+patterns during deployment such that upgrades from one environment to
+the next are simple to automate.
+
+Kolla implements a one command operation for upgrading an existing deployment
+consisting of a set of containers and configuration data to a new deployment.
+
+Kolla uses the ``x.y.z`` semver nomenclature for naming versions. Kolla's
+Liberty version is ``1.0.0`` and the Mitaka version is ``2.0.0``. The Kolla
+community commits to release z-stream updates every 45 days that resolve
+defects in the stable version in use and publish those images to the
+Docker Hub registry. To prevent confusion, the Kolla community recommends
+using an alpha identifier ``x.y.z.a`` where ``a`` represents any customization
+done on the part of the operator. For example, if an operator intends
+to modify one of the Docker files or the repos from where the originals and
+build custom images and using Liberty, the operator should start with
+version 1.0.0.0 and increase alpha for each release. Alpha tag usage is
+at discretion of the operator. The alpha identifier could be a number as
+recommended or a string of the operator's choosing.
+
+If the alpha identifier is not used, Kolla will deploy or upgrade using the
+version number information contained in the release. To customize the
+version number uncomment openstack_version in globals.yml and specify
+the version number desired.
+
+For example, to deploy a custom built Liberty version built with the
+``kolla-build --tag 1.0.0.0`` operation, change globals.yml::
+
+    openstack_version: 1.0.0.0
+
+Then run the command to deploy::
+
+    kolla-ansible deploy
+
+If using Liberty and a custom alpha number of 0, and upgrading to 1, change
+globals.yml::
+
+    openstack_version: 1.0.0.1
+
+Then run the command to upgrade::
+
+    kolla-ansible upgrade
+
+.. NOTE:: Varying degrees of success have been reported with upgrading
+  the libvirt container with a running virtual machine in it. The libvirt
+  upgrade still needs a bit more validation, but the Kolla commnity feels
+  confident this mechanism can be used with the correct Docker graph driver.
+
+.. NOTE:: The Kolla community recommends the btrfs or aufs graph drivers for
+  storing data as sometimes the LVM graph driver loses track of its reference
+  counting and results in an unremovable container.
+
+.. NOTE:: Because of system technical limitations, upgrade of a libvirt
+  container when using software emulation (``virt_driver=qemu`` in nova.conf),
+  does not work at all. This is acceptable because KVM is the recommended
+  virtualization driver to use with Nova.
 
 Diagnostics
 ===========