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A section for placement_dev.rst describing how to manage microversions, including available utility methods. Change-Id: I8ace96ed7fd721c547cedf5285833a8baa52a70a
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Placement API
Overview
Nova introduced the placement API service in the 14.0.0 Newton release. This is a separate REST API stack and data model used to track resource provider inventories and usages, along with different classes of resources. For example, a resource provider can be a compute node, a shared storage pool, or an IP allocation pool. The placement service tracks the inventory and usage of each provider. For example, an instance created on a compute node may be a consumer of resources such as RAM and CPU from a compute node resource provider, disk from an external shared storage pool resource provider and IP addresses from an external IP pool resource provider.
The types of resources consumed are tracked as classes. The service provides a set of standard resource classes (for example DISK_GB, MEMORY_MB, and VCPU) and provides the ability to define custom resource classes as needed.
References
The following specifications are based on Newton work and while they present the idea or overview for the design, implementation details may have changed or be partially complete at this time.
- Generic Resource Pools
- Compute Node Inventory
- Resource Provider Allocations
- Resource Provider Base Models
The following specifications are based on Ocata work and are subject to change.
Deployment
The placement-api service must be deployed at some point after you have upgraded to the 14.0.0 Newton release but before you can upgrade to the 15.0.0 Ocata release. This is so that the resource tracker in the nova-compute service can populate resource provider (compute node) inventory and allocation information which will be used by the nova-scheduler service in Ocata.
Steps
1. Deploy the API service
At this time the placement API code is still in Nova alongside the
compute REST API code (nova-api). So once you have upgraded nova-api to
Newton you already have the placement API code, you just need to install
the service. Nova provides a nova-placement-api WSGI script
for running the service with Apache.
Note
The placement API service is currently developed within Nova but it is designed to be as separate as possible from the existing code so that it can eventually be split into a separate project.
2. Synchronize the database
In the Newton release the Nova api database is the
only deployment option for the placement API service and the resources
it manages. After upgrading the nova-api service for Newton and running
the nova-manage api_db sync command the placement tables
will be created.
Note
There are plans to add the ability to run the placement service with a separate placement database that would just have the tables necessary for that service and not everything else that goes into the Nova api database.
3. Create accounts and update the service catalog
Create a placement service user with an admin role in Keystone.
The placement API is a separate service and thus should be registered under a placement service type in the service catalog as that is what the resource tracker in the nova-compute node will use to look up the endpoint.
Devstack sets up the placement service on the default HTTP port (80)
with a /placement prefix instead of using an independent
port.
4. Configure and restart nova-compute services
The 14.0.0 Newton nova-compute service code will begin reporting resource provider inventory and usage information as soon as the placement API service is in place and can respond to requests via the endpoint registered in the service catalog.
nova.conf on the compute nodes must be updated in the
[placement] group to contain credentials for making
requests from nova-compute to the placement-api service.
Note
After upgrading nova-compute code to Newton and restarting the
service, the nova-compute service will attempt to make a connection to
the placement API and if that is not yet available a warning will be
logged. The nova-compute service will keep attempting to connect to the
placement API, warning periodically on error until it is successful.
Keep in mind that Placement is optional in Newton, but required in
Ocata, so the placement service should be enabled before upgrading to
Ocata. nova.conf on the compute nodes will need to be updated in the
[placement] group for credentials to make requests from
nova-compute to the placement-api service.
References
The following changes were made to devstack (from oldest to newest) to enable the placement-api service and can serve as a guide for your own deployment.
https://review.openstack.org/#/c/342362/
https://review.openstack.org/#/c/363335/
https://review.openstack.org/#/c/363724/
REST API
The placement API service has its own REST API and data model.
API Reference
A full API reference is forthcoming, but until then one can get a sample of the REST API via the functional test gabbits.
Microversions
The placement API uses microversions for making incremental changes to the API which client requests must opt into.
It is especially important to keep in mind that nova-compute is a client of the placement REST API and based on how Nova supports rolling upgrades the nova-compute service could be Newton level code making requests to an Ocata placement API, and vice-versa, an Ocata compute service in a cells v2 cell could be making requests to a Newton placement API.