Are virtual machines migrated to other available hosts when HA conditions are satisfied?

Products

• VMware vCenter Server
• VMware vSphere ESXi

Issue/Introduction

This article provides information about how virtual machines are restarted on available ESX hosts when the conditions for High Availability (HA) are satisfied.

Note: This article does not cover the entire scope and functionality of HA.

Symptoms:

Environment

VMware ESXi 4.1.x Installable
VMware ESXi 4.1.x Embedded
VMware ESXi 4.0.x Embedded
VMware vCenter Server 4.1.x
VMware ESX 4.1.x
VMware ESXi 4.0.x Installable
VMware ESX 4.0.x
VMware vCenter Server 4.0.x

Resolution

When triggered, HA powers on virtual machines on other available hosts.

Note: HA does not live migrate virtual machines.

HA can be triggered by:

• A host failure (accompanied by a purple diagnostic screen).
• An unclean shutdown of the ESX host. This can occur due to a power outage, hardware issues, manual intervention.
• Network issues that cause the isolation response. A host in a VMware HA cluster might lose its console network connectivity, which causes it to become isolated from other hosts in the cluster. Isolation is a special case in which an ESX host has not actually failed, but its service console network is broken due to switch failure, Ethernet adapter failure, or some similar cause.

Based on the condition when HA is triggered, the virtual machines are shutdown based on the Virtual Machine options setting. To check the settings:

1. Right-click the HA cluster and choose Edit Settings.
2. Select Virtual Machine Options. You will see these options for a Host Isolation response:
3. • Shutdown – This option performs a clean shutdown of the virtual machine.
   • Power off – This option performs an unclean shutdown, similar to he machine going down during a power outage.
   • Leave powered on – This option leaves the virtual machine powered on. In this case, the other hosts are not able to power on this virtual machine.

When a host fails with a purple diagnostic screen or an unclean shutdown, the virtual machines running on the host also fail. HA powers up the virtual machines on other available hosts to reduce downtime.

If a virtual machine shuts down on a host isolation response due to networking issues, HA restarts the virtual machines based on the Host Isolation response option and powers on the virtual machines on other hosts.

Note: Isolation is handled as a special case of failure in HA. The isolated host intentionally shuts down its virtual machines so that they can be restarted on hosts in the cluster that are not isolated.

Additional Information

For detailed information on HA, see:

• The vSphere Availability Guide for your version of vSphere.
• VMware High Availability: Concepts. Implementation, and Best Practices