Add Deferred service events
This is a new feature for 21.04. It gets a new page. The feature was not tested during the writing of this documentation. Some text was commented out as it depends on changes to charms (READMEs), which are frozen at this time. Change-Id: I612e34436bea4db2fbf213aa02e7a6b52ca8f0cb
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Peter Matulis
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=======================
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Deferred service events
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=======================
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Overview
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--------
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Operational or maintenance procedures applied to a cloud often lead to the
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restarting of various OpenStack services and/or the calling of certain charm
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hooks. Although normal, such events can be undesirable due to the service
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interruptions they can cause.
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The deferred service events feature allows the operator the choose to prevent
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these service restarts and hook calls from occurring. These deferred events can
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then be resolved by the operator at a more opportune time.
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Situations in which these service events are prone to take place include:
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* charm upgrades
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* OpenStack upgrades (charm-managed)
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* package upgrades (non-charm-managed)
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* charm configuration option changes
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Charms
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------
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Deferred service events are supported on a per-charm basis.
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Here is the current list of deferred event-aware charms:
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* neutron-gateway
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* neutron-openvswitch
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* ovn-central
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* ovn-chassis
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* ovn-dedicated-chassis
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* rabbitmq-server
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.. COMMENT # Comment this out until the READMEs have been updated
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Deferred restarts are supported on a per-charm basis. This support will be
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mentioned in a charm's README along with any charm-specific deferred restart
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information.
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Here is the current list of deferred restart-aware charms:
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* `neutron-gateway`_
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* `neutron-openvswitch`_
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* `ovn-central`_
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* `ovn-chassis`_
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* `ovn-dedicated-chassis`_
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* `rabbitmq-server`_
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Enabling and disabling deferred service events
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----------------------------------------------
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To enable deferred service events for a charm make a configuration change:
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.. code-block:: none
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juju config <charm-name> enable-auto-restarts=False
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By default the feature is disabled.
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.. important::
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The ``enable-auto-restarts`` option can only be set post-deployment.
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To disable deferred service events:
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.. code-block:: none
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juju config <charm-name> enable-auto-restarts=True
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Identifying and resolving deferred service events
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-------------------------------------------------
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The existence of a deferred service event is exposed in the output of the
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:command:`juju status` command. The following two sections provide an example
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of how to identify and resolve each type.
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Service restarts
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~~~~~~~~~~~~~~~~
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Here the ``neutron-openvswitch/1`` unit is affected by a deferred service
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restart:
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.. code-block:: console
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App Version Status Scale Charm Store Channel Rev OS Message
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neutron-openvswitch 16.3.0 active 2 neutron-openvswitch charmstore 433 ubuntu Unit is ready
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nova-compute 21.1.2 active 2 nova-compute charmstore 537 ubuntu Unit is ready.
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Unit Workload Agent Machine Public address Ports Message
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nova-compute/0* active idle 6 172.20.0.13 Unit is ready.
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neutron-openvswitch/1 active idle 172.20.0.13 Unit is ready. Services queued for restart: openvswitch-switch
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nova-compute/1 active idle 7 172.20.0.4 Unit is ready
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neutron-openvswitch/0* active idle 172.20.0.4 Unit is ready
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To see more detail the ``show-deferred-events`` action is used:
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.. code-block:: none
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juju run-action --wait neutron-openvswitch/1 show-deferred-events
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unit-neutron-openvswitch-1:
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UnitId: neutron-openvswitch/1
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id: "67"
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results:
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Stdout: |
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none
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output: |
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hooks: []
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restarts:
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- 1618896650 openvswitch-switch Package update
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status: completed
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timing:
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completed: 2021-04-20 05:52:39 +0000 UTC
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enqueued: 2021-04-20 05:52:32 +0000 UTC
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started: 2021-04-20 05:52:33 +0000 UTC
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In this example, the message "Package update" is displayed. This signifies that
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the package management software of the host is responsible for the service
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restart request.
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Resolving deferred service restarts
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^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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To resolve a deferred service restart on a unit run the ``restart-services``
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action:
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.. code-block:: none
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juju run-action --wait neutron-openvswitch/1 restart-services deferred-only=True
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The argument ``deferred-only`` ensures that only the necessary services are
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restarted (for a charm that manages multiple services).
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.. note::
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Alternatively, the service can be restarted manually on the unit. The status
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message will be removed in due course by the charm (i.e. during the next
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``update-status`` hook execution - a maximum delay of five minutes).
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Hook calls
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~~~~~~~~~~
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Here the ``neutron-openvswitch/1`` unit is affected by a deferred hook call:
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.. code-block:: console
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App Version Status Scale Charm Store Channel Rev OS Message
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neutron-openvswitch 16.3.0 active 2 neutron-openvswitch charmstore 433 ubuntu Unit is ready. Hooks skipped due to disabled auto restarts: config-changed
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nova-compute 21.1.2 active 2 nova-compute charmstore 537 ubuntu Unit is ready
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Unit Workload Agent Machine Public address Ports Message
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nova-compute/0* active idle 6 172.20.0.13 Unit is ready
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neutron-openvswitch/1 active idle 172.20.0.13 Unit is ready. Hooks skipped due to disabled auto restarts: config-changed
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Resolving deferred hook calls
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^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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To resolve a deferred hook call on a unit run the ``run-deferred-hooks``
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action:
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.. code-block:: none
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juju run-action --wait neutron-openvswitch/1 run-deferred-hooks
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.. LINKS
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.. CHARMS
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.. _neutron-gateway: https://opendev.org/openstack/charm-neutron-gateway/src/branch/master/README.md#user-content-deferred-restarts
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.. _neutron-openvswitch: https://opendev.org/openstack/charm-neutron-openvswitch/src/branch/master/README.md#user-content-deferred-restarts
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.. _ovn-central: https://opendev.org/x/charm-ovn-central/src/branch/master/README.md#user-content-deferred-restarts
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.. _ovn-chassis: https://opendev.org/x/charm-ovn-chassis/src/branch/master/README.md#user-content-deferred-restarts
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.. _ovn-dedicated-chassis: https://opendev.org/x/charm-ovn-dedicated-chassis/src/branch/master/README.md#user-content-deferred-restarts
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.. _rabbitmq-server: https://opendev.org/openstack/charm-rabbitmq-server/src/branch/master/README.md#user-content-deferred-restarts
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@ -76,6 +76,7 @@ OpenStack Charms usage. To help improve it you can `file an issue`_ or
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app-managing-power-events
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ceph-operations
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deferred-events
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.. toctree::
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:caption: Storage
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