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This article shows you how to understand Glance, the content is concise and easy to understand, can definitely brighten your eyes, through the detailed introduction of this article, I hope you can gain something.

OpenStack Image service is provided by Glance.

Understand Image

To understand Image Service, you have to figure out what Image is and why you use Image.

In a traditional IT environment, the installation of a system is either installed from scratch by installing CD, or restored with cloning tools such as Ghost. There are several problems with these two approaches:

If there are many systems to be installed, the efficiency will be very low.

Long time and heavy workload

Manual configuration should be carried out after installation, such as installing other software, setting up IP, etc.

Backup and recovery systems are inflexible

A more efficient solution is needed in the cloud, which is called Image. Image is a template that contains the basic operating system and other software.

For example, a company needs to configure an office system for each employee, which usually requires a Win7 system plus MS office software. Here's how OpenStack plays:

First install such a virtual machine by hand.

Then snapshot the virtual machine, and you get an image

When a new employee needs an office environment, start one or more instance (virtual machines) of the image immediately

In this process, step 1 is similar to the traditional approach and requires manual operation and a certain amount of time.

But steps 2 and 3 are very fast and fully automated, usually in seconds.

And 2 or 3 steps can be done in a loop. For example, the company has a new OA system, and every employee has to have client software on their PC. Then you can manually install the OA client in an employee's virtual machine, then execute snapshot to get a new image, and then directly use the new image to create the virtual machine.

In addition, snapshot also has the role of backup, can be very convenient to restore the system.

Understand Image Service

The function of Image Service is to manage Image, allowing users to discover, obtain, and save Image.

In OpenStack, Image Service is provided by Glance, and its specific functions are as follows:

Provide REST API to enable users to query and retrieve image metadata and image itself

Support a variety of ways to store image, including ordinary file systems, Swift, Amazon S3, etc.

Snapshot Instance to create a new image

Glance architecture

Above is the architecture diagram of Glance

Glance-api

Glance-api is a service process running in the background of the system. Provide REST API to respond to image query, acquisition and storage calls.

Glance-api does not actually process requests. If it is an operation related to image metadata (metadata), glance-api will forward the request to glance-registry;. If it is an operation related to image's own access, glance-api will forward the request to the store backend of that image.

You can view the glance-api process on the control node

Glance-registry

Glance-registry is a service process running in the background of the system. The metadata responsible for processing and accessing image, such as the size and type of image.

You can view the glance-registry process on the control node

Glance supports image in various formats, including

Database

The metadata of Image is maintained in database, and the default is MySQL. You can view the database information of glance on the control node

Store backend

Glance does not store image itself. The real image is stored in backend. Glance supports a variety of backend, including

A directory on a local file system (this is the default)

GridFS

Ceph RBD

Amazon S3

Sheepdog

OpenStack Block Storage (Cinder)

OpenStack Object Storage (Swift)

VMware ESX

Which backend is used is configured in / etc/glance/glance-api.conf

In our devstack environment, the image is stored in the control node local directory / opt/stack/data/glance/images/

For other backend configurations, please refer to http://docs.openstack.org/liberty/config-reference/content/configuring-image-service-backends.html.

Check the existing image

View the saved catalog

Each image corresponds to a file in the directory, named after image's ID.

The above content is how to understand Glance. Have you learned any knowledge or skills? If you want to learn more skills or enrich your knowledge reserve, you are welcome to follow the industry information channel.

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