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Taikun OCP Guide

Table of Contents

Power Synchronization

Baremetal Power Sync

Each Baremetal conductor process runs a periodic task which
synchronizes the power state of the nodes between its database and the
actual hardware. If the value of the conductor.force_power_state_during_sync
option is set to true the power state in the database will
be forced on the hardware and if it is set to false the
hardware state will be forced on the database. If this periodic task is
enabled, it runs at an interval defined by the conductor.sync_power_state_interval
config option for those nodes which are not in maintenance. The requests
sent to Baseboard Management Controllers (BMCs) are done with a
parallelism controlled by conductor.sync_power_state_workers. The
motivation to send out requests to BMCs in parallel is to handle
misbehaving BMCs which may delay or even block the synchronization
otherwise.

Note

In deployments with many nodes and IPMI as the configured BMC
protocol, the default values of a 60 seconds power sync interval and 8
worker threads may lead to a high rate of required retries due to
client-side UDP packet loss (visible via the corresponding warnings in
the conductor logs). While Ironic automatically retries to get the power
status for the affected nodes, the failure rate may be reduced by
increasing the power sync cycle, e.g. to 300 seconds, and/or by reducing
the number of power sync workers, e.g. to 2. Pleae keep in mind,
however, that depending on the concrete setup increasing the power sync
interval may have an impact on other components relying on up-to-date
power states.

Compute-Baremetal Power Sync

Each nova-compute process in the Compute service runs a
periodic task which synchronizes the power state of servers between its
database and the compute driver. If enabled, it runs at an interval
defined by the sync_power_state_interval
config option on the nova-compute process. In case of the
compute driver being baremetal driver, this sync will happen between the
databases of the compute and baremetal services. Since the sync happens
on the nova-compute process, the state in the compute
database will be forced on the baremetal database in case of
inconsistencies. Hence a node which was put down using the compute
service API cannot be brought up through the baremetal service API since
the power sync task will regard the compute service’s knowledge of the
power state as the source of truth. In order to get around this
disadvantage of the compute-baremetal power sync, baremetal service does
power state change callbacks to the compute service using external
events.

Power State
Change Callbacks to the Compute Service

Whenever the Baremetal service changes the power state of a node, it
can issue a notification to the Compute service. The Compute service
will consume this notification and update the power state of the
instance in its database. By conveying all the power state changes to
the compute service, the baremetal service becomes the source of truth
thus preventing the compute service from forcing wrong power states on
the physical instance during the compute-baremetal power sync. It also
adds the possibility of bringing up/down a physical instance through the
baremetal service API even if it was put down/up through the compute
service API.

This change requires the nova section and the necessary
authentication options like the nova.auth_url to be defined in the
configuration file of the baremetal service. If it is not configured the
baremetal service will not be able to send notifications to the compute
service and it will fall back to the behaviour of the compute service
forcing power states on the baremetal service during the power sync. See
nova
group for more details on the available config options.

In case of baremetal stand alone deployments where there is no
compute service running, the nova.send_power_notifications config
option should be set to False to disable power state change
callbacks to the compute service.

Note

The baremetal service sends notifications to the compute service only
if the target power state is power on or
power off. Other error and None states will be
ignored. In situations where the power state change is originally coming
from the compute service, the notification will still be sent by the
baremetal service and it will be a no-op on the compute service side
with a debug log stating the node is already powering on/off.

Note

Although an exclusive lock is used when sending notifications to the
compute service, there can still be a race condition if the
compute-baremetal power sync happens to happen a nano-second before the
power state change event is received from the baremetal service in which
case the power state from compute service’s database will be forced on
the node.

Power fault and recovery

When Baremetal Power Sync is
enabled, and the Bare Metal service loses access to a node (usually
because of invalid credentials, BMC issues or networking interruptions),
the node enters maintenance mode and its fault
field is set to power failure. The exact reason is stored
in the maintenance_reason field.

As always with maintenance mode, only a subset of operations will
work on such nodes, and both the Compute service and the Ironic’s native
allocation API will refuse to pick them. Any in-progress operations will
either pause or fail.

The conductor responsible for the node will try to recover the
connection periodically (with the interval configured by the conductor.power_failure_recovery_interval
option). If the power sync is successful, the fault field
is unset and the node leaves the maintenance mode.

Note

This only applies to automatic maintenance mode with the
fault field set. Maintenance mode set manually is never
left automatically.

Alternatively, you can disable maintenance mode yourself once the
problem is resolved:

baremetal node maintenance unset <IRONIC NODE>

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