Managing Virtual Machines with Red Hat OpenShift Virtualization

A snapshot is a view of a VM at a given time.

A snapshot includes the VM's configuration and an image of the VM's disks.

Live snapshots rely on the QEMU guest agent that is running inside the VM to quiesce the file systems.

Disk snapshots rely on the back-end storage. If the back-end storage does not support snapshots, then the snapshot includes only the VM's configuration.

Clones are useful to deploy identical VMs from a model.

You use the sysprep.exe command on Microsoft Windows systems to seal the VM before cloning. For Linux systems, you use the virtctl guestfs command and then the virt-sysprep command.

DataVolume resources orchestrate the cloning process.

Live migration requires the VM's PVCs to use the ReadWriteMany access mode.

Setting a cluster node in maintenance mode requires cordoning off the node and draining the node's workload.

During the draining process, VMs that support live migration are moved uninterrupted. Other VMs are stopped and then restarted on a different node.

You create a NodeMaintenance resource to put a node into maintenance mode. You delete the resource to remove the node from maintenance mode.

You can also use the oc adm cordon, oc adm drain, and oc adm uncordon commands for managing maintenance mode.