OpenStack Glance Image Service

Glance is the image catalog and delivery service for OpenStack. It stores, discovers, and serves virtual machine images that Nova uses to boot instances. Glance handles image metadata, format validation, access control, and backend storage abstraction -- it does not care where images are physically stored, only that they are retrievable.

Supported image formats: qcow2 (default, copy-on-write, thin provisioning), raw (direct disk image, fastest I/O), vmdk (VMware), vhd/vhdx (Hyper-V), iso (CD/DVD). Backend storage options: file (local filesystem, simplest), swift (OpenStack object storage), ceph (distributed storage via RBD), cinder (block storage as image backend).

Deploy

Kolla-Ansible Configuration

globals.yml settings:

# Backend storage (choose one)
glance_backend_file: "yes"              # Local filesystem (single-node, simplest)
# glance_backend_ceph: "yes"           # Ceph RBD (multi-node, production)
# glance_backend_swift: "yes"          # Swift object storage

# File backend data directory
# glance_file_datadir: "/var/lib/glance/images"  # Default location

# Database and auth
glance_database_password: "{{ vault_glance_database_password }}"
glance_keystone_password: "{{ vault_glance_keystone_password }}"

# Image size limit (bytes, 0 = unlimited)
# glance_image_size_cap: 0

# Enable image import (web-download, glance-direct)
# enable_glance_image_import: "yes"

Deployment:

# Deploy Glance
kolla-ansible -i inventory deploy --tags glance

# Verify containers
docker ps --filter "name=glance" --format "table {{.Names}}\t{{.Status}}"
# Expected: glance_api (Up)

Post-deploy verification:

source /etc/kolla/admin-openrc.sh

# Verify Glance service in catalog
openstack service list | grep image
openstack endpoint list --service glance

# Test image upload with CirrOS (minimal test image)
wget http://download.cirros-cloud.net/0.6.2/cirros-0.6.2-x86_64-disk.img
openstack image create --file cirros-0.6.2-x86_64-disk.img \
  --disk-format qcow2 --container-format bare \
  --public cirros
openstack image list
openstack image show cirros

Image Import Task Setup

For web-download and glance-direct import methods:

# glance-api.conf [DEFAULT]
enabled_import_methods = [glance-direct, web-download, copy-image]

# glance-api.conf [task]
task_executor = taskflow
work_dir = /var/lib/glance/tasks_work_dir

Configure

Backend Storage Selection

Image Format Policies

# glance-api.conf [image_format]
disk_formats = qcow2,raw,iso          # Restrict accepted formats
container_formats = bare,docker        # Restrict container formats
default_disk_format = qcow2

Image Size Limits

# glance-api.conf [DEFAULT]
image_size_cap = 13743895347           # ~12.8 GB max image size

# Per-user quota (via Keystone project quotas)
# Managed through Oslo quotas framework

Image Caching

Glance cache stores frequently requested images locally on the API node for faster serving:

# glance-api.conf [DEFAULT]
image_cache_max_size = 10737418240     # 10 GB cache
image_cache_stall_time = 86400         # Stale after 24h
image_cache_dir = /var/lib/glance/image-cache

# Cache management
# glance-cache-manage list-cached
# glance-cache-manage list-queued
# glance-cache-manage delete-all-cached-images

Metadata Definitions

Glance supports structured metadata namespaces for organizing image properties:

# List metadata namespaces
openstack image metadata namespace list

# Create custom metadata
openstack image set --property os_type=linux \
  --property os_distro=ubuntu \
  --property os_version=22.04 \
  my-image

Property Protections

Control which users can read/write specific image properties:

# property-protections.conf
[x_billing_code]
create = role:admin
read = role:admin,role:member
update = role:admin
delete = role:admin

Image Import Methods

# Web-download: import from URL (Glance downloads it)
glance image-create-via-import --name web-image \
  --disk-format qcow2 --container-format bare \
  --import-method web-download \
  --uri http://example.com/image.qcow2

# Glance-direct: stage then import (client uploads data)
glance image-create-via-import --name direct-image \
  --disk-format qcow2 --container-format bare \
  --import-method glance-direct \
  --file local-image.qcow2

# Copy-image: copy between stores (multi-store only)
glance image-import --import-method copy-image --stores fast-store <image-id>

Operate

Image Upload and Download

# Upload image from file
openstack image create --file ubuntu-22.04.qcow2 \
  --disk-format qcow2 --container-format bare \
  --min-disk 10 --min-ram 1024 \
  --public ubuntu-22.04

# Download image to file
openstack image save --file downloaded.qcow2 <image-id>

# Upload raw image (for performance-critical workloads)
qemu-img convert -f qcow2 -O raw ubuntu-22.04.qcow2 ubuntu-22.04.raw
openstack image create --file ubuntu-22.04.raw \
  --disk-format raw --container-format bare ubuntu-22.04-raw

Format Conversion

# Convert qcow2 to raw (better I/O performance)
qemu-img convert -f qcow2 -O raw input.qcow2 output.raw

# Convert vmdk to qcow2 (import from VMware)
qemu-img convert -f vmdk -O qcow2 input.vmdk output.qcow2

# Check image info
qemu-img info image.qcow2
# Shows: format, virtual size, disk size, backing file

Image Sharing Between Projects

# Share image with another project (as image owner)
openstack image add project <image-id> <target-project-id>

# Accept shared image (as target project member)
openstack image set --accept <image-id>

# List shared images
openstack image list --shared

# Remove sharing
openstack image remove project <image-id> <target-project-id>

Snapshot Management

# Create instance snapshot (creates a Glance image)
openstack server image create --name my-snapshot my-instance

# List snapshots
openstack image list --property image_type=snapshot

# Monitor snapshot progress
openstack image show my-snapshot -c status
# States: queued -> saving -> active

Storage Usage Monitoring

# Check total image storage usage
openstack image list --long -f json | python3 -c "
import json, sys
images = json.load(sys.stdin)
total = sum(i.get('Size', 0) or 0 for i in images)
print(f'Total: {total / (1024**3):.2f} GB across {len(images)} images')
"

# Check backend storage directly (file backend)
du -sh /var/lib/docker/volumes/glance/_data/images/

# Cleanup soft-deleted images
glance-manage db purge --age_in_days 30 --max_rows 100

Image Metadata Management

# Set multiple properties
openstack image set \
  --property hw_disk_bus=scsi \
  --property hw_scsi_model=virtio-scsi \
  --property hw_vif_model=virtio \
  --property os_type=linux \
  <image-id>

# Remove a property
openstack image unset --property hw_disk_bus <image-id>

# Set hardware requirements
openstack image set --min-disk 20 --min-ram 2048 <image-id>

Troubleshoot

1. Image Upload Failures

Symptoms:

openstack image create

Diagnosis:

docker logs glance_api 2>&1 | tail -50
# Check for: disk space errors, permission denied, size limit exceeded

Common causes:

df -h /var/lib/docker/volumes/glance/

chown -R 42415:42415 /var/lib/docker/volumes/glance/

image_size_cap

2. Image Download Slow or Fails

Symptoms: Nova instance boot takes very long. Image download timeout.

Diagnosis:

# Check image size
openstack image show <image-id> -c size

# Check backend connectivity
docker exec glance_api ls -la /var/lib/glance/images/<image-id>

# Check network between glance and compute
docker logs nova_compute 2>&1 | grep -i "glance\|image\|download"

Fix:

• Enable image caching on compute nodes (nova.conf

  [image_cache]

  )
• Convert large qcow2 to raw for faster I/O
• Check network bandwidth between API and compute nodes
• Pre-cache images:

  openstack image set --property os_glance_caching=true <id>

3. Format Conversion Errors

Symptoms:

qemu-img convert

Diagnosis:

# Verify source image integrity
qemu-img check input.qcow2
# Should report: "No errors were found"

# Check format detection
qemu-img info input.qcow2

Fix:

• Corrupted source: re-download original image
• Unsupported format: convert through an intermediate format (vmdk -> qcow2 -> raw)
• Wrong format specified: verify actual format with

  qemu-img info

  before uploading

4. Image Stuck in "saving" State

Symptoms: Image shows status "saving" indefinitely.

Diagnosis:

# Check Glance API logs for write errors
docker logs glance_api 2>&1 | grep <image-id>

# Check if backend write is still in progress
ls -la /var/lib/docker/volumes/glance/_data/images/<image-id>
# File should be growing if transfer is ongoing

Fix:

• Backend write timeout: increase

  [DEFAULT] image_size_cap

  and retry
• Storage I/O error: check disk health with

  smartctl

  and

  dmesg

• Reset stuck image:

  openstack image set --status error <image-id>

  then delete and re-upload

5. Metadata Service Issues

Symptoms: Image property updates rejected. "403 Forbidden" when setting properties.

Diagnosis:

# Check property protections
docker exec glance_api cat /etc/glance/property-protections.conf

# Check RBAC policy
docker exec glance_api cat /etc/glance/policy.yaml

Fix:

• Property protection blocking: update

  property-protections.conf

  to allow the role
• RBAC denial: check

  policy.yaml

  for image modification rules
• Reserved property namespace: properties starting with

  os_

  may require admin role

Integration Points

server image create

NASA SE Cross-References