ExtensibleResourceTracking
Contents
Summary - (in progress)
There are a number of defined resources in Nova, including disk, memory and number of vCPU. The purpose of this specification is to support an extensible set of resources so that new resources can be defined for compute nodes and resource requirements for instances. These will be made available to the scheduler and allocated by the compute manager.
The resources of a compute node have limited capacity. Most, including disk, memory and vCPU, map to a physical counterpart, typically via a virtualisation technology, but it is also possible to create entirely abstract resource types that do not. As an example, a provider may chose that only one instances of a certain type should run on any compute node. This trivial example can be supported by defining a new resource for compute nodes and associating a requirement for that resource with the instance type.
Each instance has resource requirements, a specification of the quantity of each type of resource it needs. These are used by the scheduler to match it to compute nodes with sufficient available resources.
The compute manager on a host is aware of the resources available at the compute node and is responsible for their allocation and management. Because it has definitive knowledge of what resources are actually in use, the compute manager has the final say as to whether a compute node is able to host an instance.
To support extensible resource tracking we need:
A means to define resources A
The compute node view
The job of tracking the quantity of resources available on a compute node falls to the resource_tracker and the job of testing if there is sufficient capacity falls to the Claim
The scheduler view
The user view
Note that although most resources, including disk memory and vCPU, would map to a physical counterpart, typically via a virtualisation technology, it is also possible to create entirely arbitrary quantities that do not. For example, a provider may chose that only one instances of a certain type should run on a compute node. This simple case can be supported by defining a new resource for compute nodes and associating a requirement for that resource with the instance type.
The resources of a compute node (such as memory or disk space) are recorded as limited capacity that is used up as they are allocated to instances.
