Chapter 13. High Availability

The Red Hat Enterprise Virtualization Manager offers various high availability features which can be applied in a granular manner, from the level of a single virtual machine up to protection against multiple host failures. In addition, combining virtual machine high availability with out of band power management devices protects your virtual machines against storage failures.
This chapter describes Red Hat Enterprise Virtualization's high availability features, and how to configure your servers to run highly available virtual machines. In addition, this chapter provides information on configuring power management for your hosts.

13.1. What is High Availability?

High availability means that a virtual machine will be automatically restarted if its process is interrupted, for example if the virtual machine is terminated by methods other than powering off from within the guest or sending the shutdown command from the Red Hat Enterprise Virtualization Manager. When these events occur, the highly available virtual machine will be automatically restarted, either on its original host or another host in the cluster.
High availability is possible because the Red Hat Enterprise Virtualization Manager constantly monitors the physical servers, and automatically detects hardware failure. If host failure is detected, any virtual machine configured to be highly available is automatically restarted on another host in the cluster. In addition, all virtual machines are monitored, so if the virtual machine's operating system crashes, a signal is sent to automatically restart the virtual machine.
With high availability, interruption to service is minimal because virtual machines are restarted within seconds, and with no user intervention required. High availability keeps your resources balanced, as virtual machines are restarted on a host selected based on its current resource utilization, or based on any workload balancing or power saving policies that you configure. This ensures that there is sufficient capacity to restart virtual machines at all times.

13.1.1. Why Use High Availability?

High availability is recommended for virtual machines running critical workloads. It creates a secure and reliable environment where virtual machines are accessible during planned downtime or during unplanned downtime.
High availability can ensure that virtual machines are restarted in the following scenarios:
  • When a host becomes non-operational due to hardware failure.
  • When a host is put into maintenance mode for scheduled downtime.
  • When a host becomes unavailable because it has lost communication with an external storage resource.
  • When a virtual machine fails due to an operating system crash.