Instance Snapshots

In addition to the existing Zergaw CloudStack ability to snapshot individual Instance volumes, you can take an Instance Snapshot to preserve all the Instance’s data volumes as well as (optionally) its CPU/memory state. This is useful for quick restore of an Instance. For example, you can snapshot an Instance, then make changes such as software upgrades. If anything goes wrong, simply restore the Instance to its previous state using the previously saved Instance Snapshot.

The Snapshot is created using the hypervisor’s native Snapshot facility. The Instance Snapshot includes not only the data volumes, but optionally also whether the Instance is running or turned off (CPU state) and the memory contents. The Snapshot is stored in CloudStack’s primary storage.

Instance Snapshots can have a parent/child relationship. Each successive Snapshot of the same Instance is the child of the Snapshot that came before it. Each time you take an additional Snapshot of the same Instance, it saves only the differences between the current state of the Instance and the state stored in the most recent previous Snapshot. The previous Snapshot becomes a parent, and the new Snapshot is its child. It is possible to create a long chain of these parent/child Snapshots, which amount to a “redo” record leading from the current state of the Instance back to the original.

Note

freeze and thaw of Instance is maintained by the guest agent. qemu-guest-agent has to be installed in the Instance.

When the snapshotting is complete, the Instance is thawed.

Limitations on Instance Snapshots

• If an Instance has some stored Snapshots, you can’t attach new volume to the Instance or delete any existing volumes. If you change the volumes on the Instance, it would become impossible to restore the Instance Snapshot which was created with the previous volume structure. If you want to attach a volume to such an Instance, first delete its Snapshots.

• Instance Snapshots which include both data volumes and memory can’t be kept if you change the Instance’s service offering. Any existing Instance Snapshots of this type will be discarded.

• You can’t make an Instance Snapshot at the same time as you are taking a Volume Snapshot.

Using Instance Snapshots

To create an Instance Snapshot using the CloudStack UI:

1. Log in to the UI as a user or administrator.

2. Click Instances.

3. Click the name of the Instance you want to Snapshot.

4. Click the Take Instance Snapshot button.

   Note

   If a Snapshot is already in progress, then clicking this button will have no effect.

5. Provide a name and description. These will be displayed in the Instance Snapshots list.

6. (For running Instances only) If you want to include the Instance’s memory in the Snapshot, click the Memory checkbox. This saves the CPU and memory state of the Instance. If you don’t check this box, then only the current state of the Instance disk is saved. Checking this box makes the Snapshot take longer.

7. Quiesce Instance: check this box if you want to quiesce the file system on the Instance before taking the Snapshot.

   When this option is used with Zergaw CloudStack-provided primary storage, the quiesce operation is performed by the underlying hypervisor (VMware is supported). When used with another primary storage vendor’s plugin, the quiesce operation is provided according to the vendor’s implementation.

8. Click OK.

To delete a Snapshot or restore an Instance to the state saved in a particular Snapshot:

1. Navigate to the Instance as described in the earlier steps.

2. Click View Instance Snapshots.

3. In the list of Snapshots, click the name of the Snapshot you want to work with.

4. Depending on what you want to do:

   To delete the Snapshot, click the Delete button.

   To revert to the Snapshot, click the Revert button.

Note

Instance Snapshots are deleted automatically when an Instance is destroyed. You don’t have to manually delete the Snapshots in this case.