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Foreword
OpenStack recognises two types of resources on their clouds:
- Instances, which correspond to the servers or VMs. These can be image-backed, if the VM was booted from an image, or volume-backed, if it was booted from a volume. Instances are managed via the OS Glance service.
- Volumes, which correspond to storage disks which can be attached to VMs. Root disk are a special case as VMs are booted from them. Volumes are managed by the OS Cinder service.
Before restoring resources in OpenStack, it's important to understand the difference between two primary methods:
- Snapshots: These are delta copies of the root volumes attached to the VM. Snapshots are not full copies and rely on the original volume for restoration, so they are mostly useful for accident recovery. They're managed through the Cinder service.
- Backups: These are point-in-time copies of the volumes attached to VMs. Backups preserve the data within a volume and can be used to restore the volume to the exact state it was in when backed up. They're ideal for data recovery and are also managed through the Cinder service.
Choose the appropriate method based on your recovery needs: snapshots for accident prevention and recovery or backups for full data security and recovery.
Furthermore, there are two different restoration methods, according to whether the restoration replaces an existing resource or not:
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| Warning |
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| The restoration of backups or snapshots of VMs must be run outside from said VMs, specially in the case of in-place restoration, as the existing resource is completely replaced. |
| Info |
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| Legacy: previously it was possible to create image snapshots directly of the VMs. This is no longer possible as VMs are now only volume-backed. |
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Restoration of VMs Anchor RestoreSnapshots RestoreSnapshots
| RestoreSnapshots | |
| RestoreSnapshots |
Instance Snapshots
Image-backed instances
Volume-backed instances
Instance Backups
Image-backed instances
Volume-backed instances
Restoration of Volumes
Volume Snapshots
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In-place restoration of VM volume snapshots can be performed with OpenStack by replacing the root disk of an existing VM with an snapshot.
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where <volume> is the name or id of the volume just created, <instance_name> the name for the new VM, and <flavor> the flavor of the instance. The configuration details of the VM, such as flavor, networks, etc, can be chosen at the time of restoration or recovered from a previous backup if there was stored, as detailed in EWC OpenStack API access - How to create backups from VMs.
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Volume Backups
The restoration of a volume backup can also be done in-place, or by creating a new volume. Irrespective of the method, one can restore a volume backup with the command
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