After covering several articles on Neutron, we've finally arrived at the next core component of OpenStack. This time, we're introducing Glance, which is often overlooked but also extremely important.
Table of Contents
What is Glance?
在Official Document DefinitionHere's what we'll cover:
Image service (Glance) provides users with the ability to upload and discover image data to be used in conjunction with other services. Currently, it offers image files (Images) and metadata definitions.
In short, Glance is a service that allows you to store and download image files and metadata definitions.
Image Files
Glance image service includes searching, uploading, and downloading virtual machine (VM) image files. Glance provides a RESTful API that enables users to query VM image metadata and download actual image data.
There are many ways to store image files, and the most common ones today are: local filesystem, Ceph, Swift, and others.
Metadata Definitions
Glance also stores a metadata definitions catalog (Catalog) while saving image files. This provides other OpenStack services with a method to determine which metadata key names and values are applicable to OpenStack resources via API calls.
Note that Glance only manages these key-value pairs; unless you apply them to other OpenStack services, the data won’t have any effect.
Architecture
Glance’s architecture is surprisingly simple—essentially just one component: glance-api, which handles API requests from users and connects to various back-end storage systems.
Summary
Although Glance is relatively simple within OpenStack, the image storage service it provides is indispensable. The next article will cover Cinder, after which we’ll begin exploring how to implement OpenStack in real-world virtual machines.
Copyright Notice: All articles in this blog are licensed under CC BY-NC-SA 4.0 unless otherwise stated.