Add information about restoring inventory from backup

OSA has long had an inventory archive which can be used to restore
inventory in the even that something goes wrong. This change adds to the
troubleshooting guide to illustrate how to restore inventory from
backup.

Change-Id: Iacba866f1e5b534ecdb620e4890a0c710c8adf5c
Signed-off-by: Kevin Carter <kevin.carter@rackspace.com>

doc/source/admin/maintenance-tasks.rst

@@ -10,3 +10,4 @@ maintenance tasks.
 .. include :: maintenance-tasks/ansible-modules.rst
 .. include :: maintenance-tasks/containers.rst
 .. include :: maintenance-tasks/firewalls.rst
+.. include :: maintenance-tasks/inventory-backups.rst

doc/source/admin/maintenance-tasks/inventory-backups.rst

@@ -0,0 +1,41 @@
+Prune Inventory Backup Archive
+==============================
+
+The inventory backup archive will require maintenance over a long enough period
+of time.
+
+
+Bulk pruning
+------------
+
+It's possible to do mass pruning of the inventory backup. The following example will
+prune all but the last 15 inventories from the running archive.
+
+.. code-block:: bash
+
+    ARCHIVE="/etc/openstack_deploy/backup_openstack_inventory.tar"
+    tar -tvf ${ARCHIVE} | \
+      head -n -15 | awk '{print $6}' | \
+        xargs -n 1 tar -vf ${ARCHIVE} --delete
+
+
+Selective Pruning
+-----------------
+
+To prune the inventory archive selectively first identify the files you wish to
+remove by listing them out.
+
+.. code-block:: bash
+
+      tar -tvf /etc/openstack_deploy/backup_openstack_inventory.tar
+
+      -rw-r--r-- root/root    110096 2018-05-03 10:11 openstack_inventory.json-20180503_151147.json
+      -rw-r--r-- root/root    110090 2018-05-03 10:11 openstack_inventory.json-20180503_151205.json
+      -rw-r--r-- root/root    110098 2018-05-03 10:12 openstack_inventory.json-20180503_151217.json
+
+
+Now delete the targeted inventory archive.
+
+.. code-block:: bash
+
+      tar -vf /etc/openstack_deploy/backup_openstack_inventory.tar --delete openstack_inventory.json-20180503_151205.json

doc/source/admin/troubleshooting.rst

@@ -622,3 +622,30 @@ To dump traffic on the ``br-mgmt`` bridge, use ``tcpdump`` to see all
 communications between the various containers. To narrow the focus,
 run ``tcpdump`` only on the desired network interface of the
 containers.
+
+
+Restoring inventory from backup
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+OpenStack-Ansible maintains a running archive of inventory. If a change has been
+introduced into the system that has broken inventory or otherwise has caused an
+unforseen issue, the inventory can be reverted to an early version. The backup
+file ``/etc/openstack_deploy/backup_openstack_inventory.tar`` contains a set of
+timestamped inventories that can be restored as needed.
+
+Example inventory restore process.
+
+.. code-block:: bash
+
+    mkdir /tmp/inventory_restore
+    cp /etc/openstack_deploy/backup_openstack_inventory.tar /tmp/inventory_restore/backup_openstack_inventory.tar
+    cd /tmp/inventory_restore
+    tar xf backup_openstack_inventory.tar
+    # Identify the inventory you wish to restore as the running inventory
+    cp openstack_inventory.json-YYYYMMDD_SSSSSS.json /etc/openstack_deploy/openstack_inventory.json
+    cd -
+    rm -rf /tmp/inventory_restore
+
+
+At the completion of this operation the inventory will be restored to the ealier
+version.