Disable auto retry hooks for upgrades

A lesson from ServerStack upgrades.

Fix a broken link for unattended upgrades paragraph.
Then decided to create a new section for this topic,
dropping the linking and just provide a command.

Provide the above as specific pre-upgrade and post-
upgrade steps by linking from the detailed
upgrade-series-openstack page.

Drive-by: Provide a link for workload maintenance
tasks from the detailed page to the general page.

Change-Id: I69dce6387d1446e91221346ffa0cb89a7d05b414

deploy-guide/source/upgrade-overview.rst

@@ -165,6 +165,23 @@ Upgrade path:
 
 Final result: OpenStack Victoria on Ubuntu 20.04 LTS
 
+Disable automatic hook retries
+------------------------------
+
+For all upgrade types it is recommended to disable automatic hook retries
+within the model containing the cloud. This will prevent the charms from
+attempting to resolve any encountered problems, thus providing an early
+opportunity for the operator to respond accordingly.
+
+Assuming the cloud model is the current working model turn off hook retries in
+this way:
+
+.. code-block:: none
+
+   juju model-config automatically-retry-hooks=false
+
+This change should normally be reverted once the upgrade is completed.
+
 Next steps
 ----------
 

deploy-guide/source/upgrade-series-openstack.rst

@@ -116,7 +116,10 @@ The steps are as follows:
 
 #. Perform a series upgrade on the principal leader machine.
 
-   #. Perform any pre-upgrade workload maintenance tasks.
+   #. Disable :ref:`Unattended upgrades <unattended_upgrades>`.
+
+   #. Perform any pre-upgrade :ref:`workload maintenance tasks
+      <workload_maintenance>`.
 
    #. Invoke the :command:`prepare` sub-command.
 
@@ -124,6 +127,8 @@ The steps are as follows:
 
    #. Perform any post-upgrade workload maintenance tasks.
 
+   #. Re-enable Unattended upgrades.
+
    #. Reboot.
 
 #. Set the value of the (application-dependent) ``openstack-origin`` or the

deploy-guide/source/upgrade-series.rst

@@ -118,8 +118,21 @@ making any changes.
 * The Juju model comprising the cloud should be error-free (e.g. there should
   be no charm hook errors).
 
-* `Automatic package updates`_ should be disabled on the nodes to avoid
+.. _unattended_upgrades:
-  potential conflicts with the manual (or scripted) APT steps.
+
+Unattended upgrades
+-------------------
+
+Automatic package updates should be disabled on a node that is about to undergo
+a series upgrade. This is to avoid potential conflicts with the manual (or
+scripted) APT steps. One way to achieve this is with:
+
+.. code-block:: none
+
+   sudo dpkg-reconfigure -plow unattended-upgrades
+
+Once the upgrade is complete it is advised to re-enable unattended upgrades for
+security reasons.
 
 .. _workload_specific_preparations:
 
@@ -138,6 +151,8 @@ implemented series upgrade yet or simply may not work with the target series.
 Pay particular attention to SDN (software defined networking) and storage
 charms as these play a crucial role in cloud operations.
 
+.. _workload_maintenance:
+
 Workload maintenance
 ~~~~~~~~~~~~~~~~~~~~
 
@@ -321,7 +336,6 @@ appendix :doc:`Series upgrade OpenStack <upgrade-series-openstack>`.
 .. _OpenStack upgrade: upgrade-openstack.html
 .. _Known OpenStack upgrade issues: upgrade-issues.html
 .. _series upgrade: https://juju.is/docs/upgrading-series
-.. _automatic package updates: https://help.ubuntu.com/lts/serverguide/automatic-updates.html.en
 .. _Ubuntu OpenStack release cycle: https://ubuntu.com/about/release-cycle#ubuntu-openstack-release-cycle
 .. _Application leadership: https://juju.is/docs/implementing-leadership
 .. _ubuntu: https://jaas.ai/ubuntu