Placement API support for instance reservation¶

Use Cases¶

• A user wants to reserve instance resources with arbitrary affinity policy.
• A user wants to reserve more instances than the number of hosts.

When creating a host:¶

1. Get hypervisor information and store it into the computehosts table.

2. Create a nested resource provider as a child of the compute node resource provider by calling the Create resource provider API. The UUID of the compute node resource provider can be retrieved by calling the List resource providers API with the name option query, e.g. GET /placement/resource_proiders?name=compute-1.

   The child resource provider is referred to as ‘reservation provider’ in the following sections.

   Create reservation provider request body example:

   POST /placement/resource_providers

{
    "name": "blazar_compute-1",
    "parent_provider_uuid": "542df8ed-9be2-49b9-b4db-6d3183ff8ec8"
}

3. Add the host into the freepool.

When creating a lease:¶

1. Look for available resources with arbitrary affinity policy.

2. Update the computehost_allocations table.

3. Create a custom resource class CUSTOM_RESERVATION_{reservation UUID} by calling the Create resource class API.

   Create resource class request body example:

   POST /placement/resource_classes

{
    "name": "CUSTOM_RESERVATION_4D17D41A_830D_47B2_91C7_4F9FC0AE611E"
}

4. Create a private flavor which has resources:CUSTOM_RESERVATION_{reservation UUID}=1 in its extra_spec.

When starting a lease:¶

1. Add the custom resource class CUSTOM_RESERVATION_{reservation UUID} into the reservation provider’s inventory by calling the Update resource provider inventories API with the total parameter which equals to the amount of instances reserved for the host.

   Update resource provider inventories request body example:

   PUT /placement/resource_providers/{reservation_provider_uuid}/inventories

{
    "inventories": {
        "CUSTOM_RESERVATION_4D17D41A_830D_47B2_91C7_4F9FC0AE611E": {
            "total": 3,
            "allocation_ratio": 1.0,
            "min_unit": 1,
            "max_unit": 1,
            "step_size": 1
        },
        "snip"
    },
    "resource_provider_generation": 5
}

2. Add the lease owner’s project to the private flavor access rights list.

When launching instances (from user point of view):¶

1. A lease owner uses the private flavor and the instance is launched on the reserved host which has the CUSTOM_RESERVATION_{reservation UUID} in it’s child resource provider inventory, i.e. reservation provider inventory.

   Consumption of CUSTOM_RESERVATION_{reservation UUID} resources in the reservation provider inventory is claimed by the Nova scheduler. It means that usage of reserved resources is automatically tracked by the Placement.

When terminating a lease:¶

1. Delete related instances and the private flavor.
2. Remove the CUSTOM_RESERVATION_{reservation UUID} class from the reservation provider’s inventory by calling the Delete resource provider inventory API.
3. Delete the CUSTOM_RESERVATION_{reservation_UUID} resource class by calling the Delete resource class API.

When deleting a host:¶

1. Delete the reservation provider which is associated with the host by calling the Delete resource provider API.
2. Remove the host from the freepool.
3. Update the computehosts table.

Alternatives¶

Data model impact¶

The affinity column of the instance_reservations table is changed to allow NULL. NULL means no affinity policy is applied while True means affinity is applied and False means anti-affinity is applied.

The instance_reservations table:

ALTER TABLE instance_reservations
    ALTER COLUMN affinity NULL;

After the previous instance reservation is deprecated and completely removed, drop the following columns in the instance_reservations table:

ALTER TABLE instance_reservations
    DROP COLUMN aggregate_id, server_group_id;

REST API impact¶

The affinity parameter of the Create lease API is changed to be an optional parameter. If the affinity parameter is not given, no affinity policy is applied.

Security impact¶

None

Notifications impact¶

None

Other end user impact¶

None

Performance Impact¶

None

Other deployer impact¶

• The Placement API has to be newer than or equal to Ver. 1.29.
• To upgrade from the previous version, run the DB upgrade script and the instance_reservations table schema will be updated.

Developer impact¶

None

Assignee(s)¶

Primary assignee:

<tetsuro>

Other contributors:

<hiro-kobayashi>

Work Items¶

Base:

• Update DB schema: update the instance_reservations table.
• Add placement library in blazar/utils/openstack module.

To support the host creation:

• Update the create_computehost() of the host plugin to call Placement APIs and update related tables.

To support the host deletion:

• Update the delete_computehost() of the host plugin to delete Placement related resources.

To support the lease creation:

• Update the query_available_hosts() to return how many instance can be launched on each available host.
• Update the pickup_hosts() to support arbitrary affinity policy.
• Update the reserve_resource() and update_reservation() to support multiple allocations which have the same pair of reservation_id and computehost_id.
• Update the _create_resources() of the instance plugin to create the CUSTOM_RESERVATION_{reservation UUID} class and add it into the private flavor extra specs.

To support starting the lease:

• Update the on_start() of the instance plugin to add the CUSTOM_RESERVATION_{reservation UUID} into the reservation provider inventory. The total parameter equals to the number of entries of the computehost_allocations table which have the same reservation id and computehost id.

To support launching reserved instances:

• Update the BlazarFilter.

To support termination of the lease:

• Update the on_end() of the instance plugin to remove the custom resource from the reservation provider inventory and delete the class itself.

Others:

• Update the api module and the python-blazarclient to support arbitrary affinity policies.
• Update the blazar-dashboard to support arbitrary affinity policies.
• Update documentation.