Backing up your VM

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This article is a draft

This is not a complete article: This is a Draft, a work in progress that is intended to be published into an article, which may or may not be ready for inclusion in the main wiki. It should not necessarily be considered factual or authoritative.

Parent page: Cloud

It is often a good idea to backup your VM. The two main VM flavors persistent (p) and compute (c) have different behaviors and backups should be considered differently for each.

Persistent VMs

Persistent VMs are designed to boot from volumes (see booting from a volume) thus creating a copy of the volume(s) the VM has attached to it will produce a backup. However this would not preserver things like VM flavor, public IP, and security rules. The best way to create a copy of a volume for backup purposes is to create an image from that volume. An image can be downloaded and reused to create multiple new VMs, can be accessed by VirtualBox on your Desktop or laptop, and uploaded to other clouds.

To be able to create an image from a volume, that volume must be detached from the VM. In addition, if the volume is the root volume of the VM it can not be detached unless the VM is deleted. If you are sure that when you created the VM you did not check the box "Delete Volume on Instance Delete" then you can delete your VM knowing you will not loose any data. However, if you are unsure if you checked this box OpenStack, unfortunately, doesn't tell you if this box was checked when you created a VM. One trick which maybe useful for getting around this, is to create a snapshot of the volume provided you have a storage quota which allows it (Snapshots count towards your storage quota). Since volumes can not be deleted if there is a volume snapshot created from them, when you delete the VM the volume will not be deleted even if you checked the box.

At this point all the volumes you wish to create images of should be in the "Available" state. To create an image from a volume, select 'Upload to Image' from the drop down menu for the volume. Select the 'QCOW2' disk format and give your image a name. There are several formats for disk images but QCOW2 works well with OpenStack and typically does not take up as much space as "Raw" images. Other formats "vmdk" and "vdi" can be useful when working with other virtualization tools such as VirtualBox.

Once you have created images of all the volumes you wish to backup you can then re-create your VM booting from the original VM's root volume and attaching any additional volumes you may have had attached to the original VM.

What about volume snapshots?

Another alternative might be to create a snapshot of a volume, which will save the state of a volume at the time the snapshot was created, however volume snapshots depend on the original volume remaining intact and as such are not ideal for backups. It is also not possible to download volume snapshots as they depend on the original volume. However, they do allow you to create a new volume from a snapshot of a volume at a given point in time. For example, if there were file changes since the last volume snapshot you would like to revert. Or if there were file changes specific to that VM which should not be included in other VMs.

What about VM snapshots?

Unfortunately, OpenStack uses the word "snapshot" to mean two different things. There are volume snapshosts, as discussed above, and snapshots of VMs. Snapshots of VMs behave in different ways depending on the flavor of your VM. If you have a persistent VM and create a snapshot of the VM, OpenStack creates a nearly empty image, which contains pointers to volume snapshots. These pointers point to volume snapshot(s) of the persistent VM's boot volume and any attached volumes which were created as part of creating a snapshot of the VM. You can then create a new VM (boot from image (creates a new volume)) which will create new volumes from the snapshots of the volumes taken previously, boot a new VM from the root volume and attach any other duplicated volumes.

Compute VMs

As with creating backups of persistent VMs, the main goal is to create an image of at least the root drive, and perhaps also other attached volumes if needed. However, differences with compute flavor VMs change the process of creating that image. Compute VMs are not designed to boot from volumes accessed over the network as persistent VMs are, instead they are meant to be booted from disk images which reside locally on the computer which is actually running your VM. This means there is no volume which you can click on in the OpenStack dashboard to create an image of your root disk. Instead you can do this by clicking "Create Snapshot" on your VM's drop down menu on the "Instances" tab. As with creating a snapshot with a persistent VM this creates an image. However, in this case the image is not nearly empty containing only pointers to volume snapshots. Instead the image contains a copy of the VMs root drive.

Compute VMs also come with an extra data drive mounted at /mnt, the data on this drive is not captured in the image created of a compute VM. Other arrangements must be made to save this data, such as coping it off the disk before the VM is terminated.