OpenStack Placement API is a component of the OpenStack cloud computing platform that provides resource discovery and tracking capabilities. It serves as a central service for managing and tracking the available resources (compute, storage, and network) within an OpenStack deployment.
The main purpose of the Placement API is to enable efficient and accurate scheduling of resources for virtual machines and other instances in an OpenStack cloud. It allows the cloud scheduler to make informed decisions about where to place instances based on the available resources and their characteristics.
Here are some key points about the OpenStack Placement API:
- Resource Tracking: The Placement API maintains a database of available resources and their associated traits. Resources can include compute hosts, storage devices, network resources, and more. It tracks the capacity, capabilities, and usage of these resources, allowing for efficient resource allocation.
- Resource Provider Hierarchy: The Placement API organizes resources in a hierarchical structure. At the top level, you have the “root provider,” which represents the entire cloud infrastructure. Beneath the root provider, you can have multiple nested providers representing different regions, availability zones, or other logical groupings of resources.
- Resource Classes and Traits: Resources in the Placement API are categorized using resource classes and traits. Resource classes represent a type of resource, such as CPU, memory, or storage. Traits, on the other hand, represent specific characteristics or capabilities of a resource class, such as hardware acceleration, NUMA topology, or specialized hardware features.
- Inventory and Allocation: The Placement API tracks the inventory of resources available in each provider and allows for resource allocation. When a compute host is added to the cloud, its inventory is registered with the Placement API. Instances request resources through the Placement API, which checks the available inventory and allocates the requested resources if they are available.
- Filtering and Weighing: The Placement API provides a filtering and weighing mechanism for the scheduler. Filters allow the scheduler to specify resource requirements and constraints when selecting a suitable host for an instance. Weights are used to prioritize available hosts based on different criteria like utilization, proximity, or custom policies.
- RESTful API: The Placement API is accessed through a RESTful API, which allows clients (such as the Nova scheduler) to interact with it. The API supports operations like creating and managing resource providers, managing resource inventory, making allocation requests, and retrieving resource information.
- Integration with Nova: The Nova compute service in OpenStack extensively uses the Placement API. The Nova scheduler queries the Placement API to discover available resources, select appropriate hosts for instances, and track resource allocations. The Placement API provides a standardized interface for resource tracking and scheduling across different compute nodes.
The Placement API plays a crucial role in enabling efficient resource utilization and allocation within an OpenStack cloud. By providing a central resource management service, it helps optimize workload placement, improve performance, and support advanced scheduling features in OpenStack deployments.