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Glance

Updated Sep 15, 2023 ·

Overview​

Glance stores, manages, and serves images for OpenStack. These images include virtual machine boot disks and other compute-related images. Compute nodes request images from Glance when launching instances.

  • Stores virtual machine and bare metal images
  • Provides APIs to manage and retrieve images
  • Can cache locally at compute nodes for faster access

Glance handles large image data efficiently and ensures a reliable image management system across OpenStack nodes.

Glance Architecture​

Glance is a standalone service with several key components:

ComponentDescription
Glance APIHandles all requests to store, retrieve, and manage images
Glance RegistryStores image metadata like size and disk format; private service, not exposed to users
Metadata definitionsAllows adding custom metadata to images
DatabaseStores Glance state; typically MySQL or SQLite
Glance StoreManages the actual image storage with various backends

Glance can store images for multiple services, including Compute, Magnum, Trove, and Sahara.

Glance Storage Backends​

Glance supports different storage backends depending on deployment needs. Vendors may also provide additional storage drivers with optimized features.

Store backend types supported in community version:

  • File, Filesystem
  • HTTP/HTTPS
  • Swift
  • Rdb
  • Sheepdog
  • Cinder
  • vSphere

Vendor-supported backend types:

  • Amazon S3
  • GridFS
  • Datera Elastic Data Fabric (EDF)

File Backend​

File backend stores images as files on the node, suitable for single-node deployments.

Sample glance-api.conf for setting up default file storage:

[glance_store]
stores = file, http
default_store = file
filesystem_store_datadir = /var/lib/glance/images/

Note:

  • stores defines enabled storage drivers
  • default_store sets the primary backend
  • filesystem_store_datadir is the directory storing images

External Backends​

Glance can use external storage backends like Swift and Ceph to store images. This allows high availability and better performance for large deployments.

Swift Backend Configuration​

You configure these settings in /etc/glance/glance-api.conf.

[glance_store]
stores = swift,http
default_store = swift
default_swift_reference = swift_image_store
swift_store_auth_insecure = False
swift_store_auth_address = http://swift.example.com:5000/v3
swift_store_endpoint_type = internalURL
swift_store_container = glance_images
swift_store_config_file = /etc/glance/glance-store.conf
swift_store_user = glance_user
swift_store_key = password123
swift_store_large_object_size = 5120
swift_store_large_object_chunk_size = 200
swift_store_create_container_on_put = True
swift_store_region = RegionOne
swift_store_retry_get_count = 5

Swift Keystone Authentication​

Glance can use Keystone credentials to authenticate to Swift. You define these in a separate configuration file, such as /etc/glance/glance-store.conf.

[swift_image_store]
user = service:glance
key = openstack
user_domain_id = default
project_domain_id = default
auth_version = 3
auth_address = http://10.0.0.11:5000/v3

Note:

  • user is the Keystone user Glance uses to access Swift
  • key is the password for that user
  • user_domain_id and project_domain_id define the Keystone domain context
  • auth_version specifies the Keystone API version
  • auth_address is the Keystone authentication URL

High Availability and Performance​

You can also deploy multiple Glance API instances behind a load balancer. This improves availability and performance, as multiple servers can serve large image files to compute nodes simultaneously.

Glance Image Cache​

Caching improves performance by storing frequently requested images on the Glance API server.

  • Without cache, every request fetches images from the backend
  • With cache, the API server serves repeated requests locally

You can enable caching in g;ance-api-paste.imi, and then configure the parameters in glance-api.conf and glance-cache.conf to optimize performance for multiple compute nodes.

[cache]
enabled = true
directory = /var/lib/glance/cache
image_cache_size = 10737418240  # 10 GB cache size

Installation and Configuration​

Setting up Glance involves these steps:

  1. Create a SQL database for Glance (shared MySQL cluster or dedicated instance)
  2. Create Glance user in Keystone and grant admin privileges
  3. Register the Glance service and endpoints using OpenStack CLI
  4. Install and configure the chosen storage backend
  5. Configure glance-api.conf with DB, Keystone, store, and cache parameters
  6. Populate the Glance database and restart Glance services

For more information, please see Installing Glance.