Overview

The glance charm provides the Glance image service for OpenStack. It is intended to be used alongside the other OpenStack components.

Usage

Glance may be deployed in a number of ways. This charm focuses on 3 main configurations. All require the existence of the other core OpenStack services deployed via Juju charms, specifically: mysql, keystone and nova-cloud-controller. The following assumes these services have already been deployed.

Configuration

This section covers common and/or important configuration options. See file config.yaml for the full list of options, along with their descriptions and default values. See the Juju documentation for details on configuring applications.

openstack-origin

The openstack-origin option states the software sources. A common value is an OpenStack UCA release (e.g. 'cloud:xenial-queens' or 'cloud:bionic-ussuri'). See Ubuntu Cloud Archive. The underlying host's existing apt sources will be used if this option is not specified (this behaviour can be explicitly chosen by using the value of 'distro').

pool-type

The pool-type option dictates the Ceph storage pool type. See sections 'Ceph pool type' and 'Ceph backed storage' for more information.

Ceph pool type

Ceph storage pools can be configured to ensure data resiliency either through replication or by erasure coding. This charm supports both types via the pool-type configuration option, which can take on the values of 'replicated' and 'erasure-coded'. The default value is 'replicated'.

For this charm, the pool type will be associated with Glance images.

Note: Erasure-coded pools are supported starting with Ceph Luminous.

Replicated pools

Replicated pools use a simple replication strategy in which each written object is copied, in full, to multiple OSDs within the cluster.

The ceph-osd-replication-count option sets the replica count for any object stored within the 'glance' rbd pool. Increasing this value increases data resilience at the cost of consuming more real storage in the Ceph cluster. The default value is '3'.

Important: The ceph-osd-replication-count option must be set prior to adding the relation to the ceph-mon (or ceph-proxy) application. Otherwise, the pool's configuration will need to be set by interfacing with the cluster directly.

Erasure coded pools

Erasure coded pools use a technique that allows for the same resiliency as replicated pools, yet reduces the amount of space required. Written data is split into data chunks and error correction chunks, which are both distributed throughout the cluster.

Note: Erasure coded pools require more memory and CPU cycles than replicated pools do.

When using erasure coded pools for Glance images two pools will be created: a replicated pool (for storing RBD metadata) and an erasure coded pool (for storing the data written into the RBD). The ceph-osd-replication-count configuration option only applies to the metadata (replicated) pool.

Erasure coded pools can be configured via options whose names begin with the ec- prefix.

Important: It is strongly recommended to tailor the ec-profile-k and ec-profile-m options to the needs of the given environment. These latter options have default values of '1' and '2' respectively, which result in the same space requirements as those of a replicated pool.

See Ceph Erasure Coding in the OpenStack Charms Deployment Guide for more information.

Local Storage

In this configuration, Glance uses the local storage available on the server to store image data:

juju deploy glance
juju add-relation glance keystone
juju add-relation glance mysql
juju add-relation glance nova-cloud-controller

Swift backed storage

Glance can also use Swift Object storage for image storage. Swift is often deployed as part of an OpenStack cloud and provides increased resilience and scale when compared to using local disk storage. This configuration assumes that you have already deployed Swift using the swift-proxy and swift-storage charms:

juju deploy glance
juju add-relation glance keystone
juju add-relation glance mysql
juju add-relation glance nova-cloud-controller
juju add-relation glance swift-proxy

This configuration can be used to support Glance in HA/Scale-out deployments.

Ceph backed storage

In this configuration, Glance uses Ceph based object storage to provide scalable, resilient storage of images. This configuration assumes that you have already deployed Ceph using the ceph charm:

juju deploy glance
juju add-relation glance keystone
juju add-relation glance mysql
juju add-relation glance nova-cloud-controller
juju add-relation glance ceph-mon

This configuration can also be used to support Glance in HA/Scale-out deployments.

Note: Glance acts as a Ceph client in this case which requires IP (L3) connectivity to Ceph monitors and OSDs. For MAAS-based deployments this can be addressed with network spaces (see section 'Network spaces' below).

High availability

When more than one unit is deployed with the hacluster application the charm will bring up an HA active/active cluster.

There are two mutually exclusive high availability options: using virtual IP(s) or DNS. In both cases the hacluster subordinate charm is used to provide the Corosync and Pacemaker backend HA functionality.

See OpenStack high availability in the OpenStack Charms Deployment Guide for details.

Important: Glance in an HA configuration must be backed by either Ceph or Swift.

Glance metering

In order to do Glance metering with Ceilometer, an AMQP relation is required e.g.

juju deploy glance
juju deploy rabbitmq-server
juju deploy ceilometer-agent
...
juju add-relation glance rabbitmq-server
juju add-relation glance ceilometer-agent
...

Network spaces

This charm supports the use of Juju network spaces. This feature optionally allows specific types of the application's network traffic to be bound to subnets that the underlying hardware is connected to.

Note: Spaces must be configured in the backing cloud prior to deployment.

API endpoints can be bound to distinct network spaces supporting the network separation of public, internal and admin endpoints.

Glance acts as a Ceph client and needs IP connectivity to Ceph monitors and OSDs. Binding the ceph endpoint to a space can solve this problem in case monitors and OSDs are located on a single L2 broadcast domain (if they are not, static or dynamic routes need to be used in addition to spaces).

Access to the underlying MySQL instance can also be bound to a specific space using the shared-db relation.

To use this feature, use the --bind option when deploying the charm:

juju deploy glance --bind \
   "public=public-space \
    internal=internal-space \
    admin=admin-space \
    shared-db=internal-space \
    ceph=ceph-access-space"

Alternatively, these can also be provided as part of a juju native bundle configuration:

    glance:
      charm: cs:xenial/glance
      num_units: 1
      bindings:
        public: public-space
        admin: admin-space
        internal: internal-space
        shared-db: internal-space
        ceph: ceph-access-space

Note: Existing glance units configured with the os-admin-network, os-internal-network, or os-public-network options will continue to honour them. Furthermore, these options override any space bindings, if set.

Policy overrides

Policy overrides is an advanced feature that allows an operator to override the default policy of an OpenStack service. The policies that the service supports, the defaults it implements in its code, and the defaults that a charm may include should all be clearly understood before proceeding.

Caution: It is possible to break the system (for tenants and other services) if policies are incorrectly applied to the service.

Policy statements are placed in a YAML file. This file (or files) is then (ZIP) compressed into a single file and used as an application resource. The override is then enabled via a Boolean charm option.

Here are the essential commands (filenames are arbitrary):

zip overrides.zip override-file.yaml
juju attach-resource glance policyd-override=overrides.zip
juju config glance use-policyd-override=true

See appendix Policy overrides in the OpenStack Charms Deployment Guide for a thorough treatment of this feature.

Bugs

Please report bugs on Launchpad.

For general charm questions refer to the OpenStack Charm Guide.