6.4 KiB
Deferred service events
Overview
Operational or maintenance procedures applied to a cloud often lead to the restarting of various OpenStack services and/or the calling of certain charm hooks. Although normal, such events can be undesirable due to the service interruptions they can cause.
The deferred service events feature allows the operator the choose to prevent these service restarts and hook calls from occurring. These deferred events can then be resolved by the operator at a more opportune time.
Situations in which these service events are prone to take place include:
- charm upgrades
- OpenStack upgrades (charm-managed)
- package upgrades (non-charm-managed)
- charm configuration option changes
Charms
Deferred service events are supported on a per-charm basis.
Here is the current list of deferred event-aware charms:
- neutron-gateway
- neutron-openvswitch
- ovn-central
- ovn-chassis
- ovn-dedicated-chassis
- rabbitmq-server
Deferred restarts are supported on a per-charm basis. This support will be mentioned in a charm's README along with any charm-specific deferred restart information.
Here is the current list of deferred restart-aware charms:
Enabling and disabling deferred service events
To enable deferred service events for a charm make a configuration change:
juju config <charm-name> enable-auto-restarts=False
By default the feature is disabled.
Important
The enable-auto-restarts
option can only be set
post-deployment.
To disable deferred service events:
juju config <charm-name> enable-auto-restarts=True
Identifying and resolving deferred service events
The existence of a deferred service event is exposed in the output of
the juju status
command. The following two sections provide an example of how to
identify and resolve each type.
Service restarts
Here the neutron-openvswitch/1
unit is affected by a
deferred service restart:
App Version Status Scale Charm Store Channel Rev OS Message
neutron-openvswitch 16.3.0 active 2 neutron-openvswitch charmstore 433 ubuntu Unit is ready
nova-compute 21.1.2 active 2 nova-compute charmstore 537 ubuntu Unit is ready.
Unit Workload Agent Machine Public address Ports Message
nova-compute/0* active idle 6 172.20.0.13 Unit is ready.
neutron-openvswitch/1 active idle 172.20.0.13 Unit is ready. Services queued for restart: openvswitch-switch
nova-compute/1 active idle 7 172.20.0.4 Unit is ready
neutron-openvswitch/0* active idle 172.20.0.4 Unit is ready
To see more detail the show-deferred-events
action is
used:
juju run-action --wait neutron-openvswitch/1 show-deferred-events
unit-neutron-openvswitch-1:
UnitId: neutron-openvswitch/1
id: "67"
results:
Stdout: |
none
output: |
hooks: []
restarts:
- 1618896650 openvswitch-switch Package update
status: completed
timing:
completed: 2021-04-20 05:52:39 +0000 UTC
enqueued: 2021-04-20 05:52:32 +0000 UTC
started: 2021-04-20 05:52:33 +0000 UTC
In this example, the message "Package update" is displayed. This signifies that the package management software of the host is responsible for the service restart request.
Resolving deferred service restarts
To resolve a deferred service restart on a unit run the
restart-services
action:
juju run-action --wait neutron-openvswitch/1 restart-services deferred-only=True
The argument deferred-only
ensures that only the
necessary services are restarted (for a charm that manages multiple
services).
Note
Alternatively, the service can be restarted manually on the unit. The
status message will be removed in due course by the charm (i.e. during
the next update-status
hook execution - a maximum delay of
five minutes).
Hook calls
Here the neutron-openvswitch/1
unit is affected by a
deferred hook call:
App Version Status Scale Charm Store Channel Rev OS Message
neutron-openvswitch 16.3.0 active 2 neutron-openvswitch charmstore 433 ubuntu Unit is ready. Hooks skipped due to disabled auto restarts: config-changed
nova-compute 21.1.2 active 2 nova-compute charmstore 537 ubuntu Unit is ready
Unit Workload Agent Machine Public address Ports Message
nova-compute/0* active idle 6 172.20.0.13 Unit is ready
neutron-openvswitch/1 active idle 172.20.0.13 Unit is ready. Hooks skipped due to disabled auto restarts: config-changed
Resolving deferred hook calls
To resolve a deferred hook call on a unit run the
run-deferred-hooks
action:
juju run-action --wait neutron-openvswitch/1 run-deferred-hooks