Manage Unified Limits Quotas

Note

This section provides deployment information about the quota feature. For end-user information about quotas, including information about the type of quotas available, refer to the user guide.

Since the Nova 28.0.0 (2023.2 Bobcat) release, it is recommended to use Keystone unified limits for Nova quota limits.

For information about legacy quota limits, see the legacy quota documentation.

To enable unified limits quotas, set the quota driver in the Nova configuration:

[quota]
driver = nova.quota.UnifiedLimitsDriver

Quota limits are set and retrieved for enforcement using the Keystone API.

To prevent system capacities from being exhausted without notification, you can set up quotas. Quotas are operational limits. For example, the number of servers allowed for each project can be controlled so that cloud resources are optimized. Quotas can be enforced at both the global (default) and the project level.

Resource usage is counted from the placement service with unified limits.

Checking quota

When calculating limits for a given resource and project, the following checks are made in order:

  1. Project-specific limits

    Depending on the resource, is there a project-specific limit on the resource in Keystone limits? If so, use that as the limit. You can create these resource limits using:

    $ openstack limit create --service nova --project <project> --resource-limit 5 servers

  2. Default limits

    Use the Keystone registered limit for the resource as the limit. You can create these default limits using:

    $ openstack registered limit create --service nova --default-limit 5 servers

Rechecking quota

If quota.recheck_quota is True (this is the default), Nova will perform a second quota check after allocating resources. The first quota check is performed before resources are allocated. Rechecking quota ensures that quota limits are strictly enforced and prevents any possibility of resource allocation going over the quota limit in the event of racing parallel API requests.

It can be disabled by setting quota.recheck_quota to False if strict quota enforcement is not important to the operator.

Quota usage from placement

With unified limits quotas, it is required that quota resource usage is counted from placement. As such, the quota.count_usage_from_placement configuration option is ignored when quota.driver is set to nova.quota.UnifiedLimitsDriver.

There are some things to note when quota resource usage is counted from placement:

  • Counted usage will not be accurate in an environment where multiple Nova deployments are sharing a placement deployment because currently placement has no way of partitioning resource providers between different Nova deployments. Operators who are running multiple Nova deployments that share a placement deployment should not use the nova.quota.UnifiedLimitsDriver.

  • Behavior will be different for resizes. During a resize, resource allocations are held on both the source and destination (even on the same host, see https://bugs.launchpad.net/nova/+bug/1790204) until the resize is confirmed or reverted. Quota usage will be inflated for servers in this state.

  • The populate_queued_for_delete and populate_user_id online data migrations must be completed before usage can be counted from placement. Until the data migration is complete, the system will fall back to legacy quota usage counting from cell databases depending on the result of an EXISTS database query during each quota check. Use nova-manage db online_data_migrations to run online data migrations.

  • Behavior will be different for unscheduled servers in ERROR state. A server in ERROR state that has never been scheduled to a compute host will not have placement allocations, so it will not consume quota usage for cores and ram.

  • Behavior will be different for servers in SHELVED_OFFLOADED state. A server in SHELVED_OFFLOADED state will not have placement allocations, so it will not consume quota usage for cores and ram. Note that because of this, it will be possible for a request to unshelve a server to be rejected if the user does not have enough quota available to support the cores and ram needed by the server to be unshelved.

Configuration

View and update default quota values

To list all default quotas for a project, run:

$ openstack registered limit list

Note

This lists default quotas for all services and not just nova.

To show details about a default limit, run:

$ openstack registered limit show <registered-limit-id>

To create a default quota limit, run:

$ openstack registered limit create --service nova --default-limit <value> <resource-name>

Note

Creating or updating registered limits requires a system-scoped authorization token by default. See the Keystone tokens documentation for more information.

To update a default quota value, run:

$ openstack registered limit set --default-limit <value> <registered-limit-id>

To delete a default quota limit, run:

$ openstack registered limit delete <registered-limit-id> [<registered-limit-id> ...]

View and update quota values for a project

To list quotas for a project, run:

$ openstack limit list --project <project>

Note

This lists project quotas for all services and not just nova.

To list quotas for all projects, you must have a system-scoped authorization token and run:

$ openstack limit list

To show details about a quota limit, run:

$ openstack limit show <limit-id>

To create a quota limit for a project, run:

$ openstack limit create --service nova --project <project> --resource-limit <value> <resource-name>

To update quotas for a project, run:

$ openstack limit set --resource-limit <value> <limit-id>

To delete quotas for a project, run:

$ openstack limit delete <limit-id> [<limit-id> ...]

Migration to unified limits quotas

There is a nova-manage limits migrate_to_unified_limits command available to help with moving from legacy Nova database quotas to Keystone unified limits quotas. The command will read quota limits from the Nova database and call the Keystone API to create the corresponding unified limits. Per-user quota limits will not be copied into Keystone because per-user quotas are not supported in unified limits.