Glance is an OpenStack service that provides image services for use with virtual machines (VMs) and containers. It acts as a central repository for storing, discovering, and retrieving virtual machine images, disk images, and other image artifacts.
The Glance API is the primary interface through which users and other OpenStack services interact with Glance. It offers a set of RESTful endpoints that allow users to perform various operations on images, such as uploading, querying, and managing them. Here’s a breakdown of the main components and functionalities of the Glance API:
- Image Management: The Glance API allows users to upload, register, and manage images. An image represents a single file or a disk image that can be used to create VM instances. Users can upload images from their local systems or register them by providing the image location and metadata. The API supports various image formats, including RAW, VHD, VDI, VMDK, and more.
- Image Metadata: Glance allows users to associate metadata with their images, providing additional information about the image. This metadata can include properties like name, description, size, format, architecture, operating system, and more. The metadata helps users to search, filter, and categorize images for easier discovery and management.
- Image Sharing: Glance supports image sharing between different projects or tenants within an OpenStack deployment. Users can make their images public, allowing other users to access and use them. Additionally, users can share images selectively with specific projects or tenants, providing controlled access to their images.
- Image Versioning: Glance API supports versioning of images, allowing users to manage different versions of the same image. Users can upload new versions of an image while retaining the existing versions. This enables users to maintain backward compatibility and update images without affecting the instances already using older versions.
- Image Lifecycle Management: The Glance API provides features for managing the lifecycle of images. Users can perform operations like updating image properties, deleting images, and setting image visibility. They can also control the availability of images, such as making them active, deactivated, or queued for deletion.
- Image Filtering and Searching: Glance API supports filtering and searching capabilities to help users find specific images based on criteria like name, format, size, metadata, and more. Users can retrieve a list of images that match their search criteria, facilitating efficient image discovery.
- Image Copying and Converting: Glance allows users to copy images within or between OpenStack deployments. This feature is useful for distributing images across different regions or sharing images across different OpenStack clouds. Users can also convert images between different formats using Glance, making it compatible with various virtualization platforms.
- Image Importing and Exporting: Glance API provides mechanisms to import and export images from external sources. Users can import images from external URLs or export images to a specified destination. This capability allows users to migrate images between different storage systems or import images from external repositories.
The Glance API is typically used by other OpenStack services such as Nova (compute service) and Horizon (web-based dashboard) to perform image-related operations. It provides a standardized and scalable way to manage images within an OpenStack cloud environment.