What It Is: VMware High Availability (HA) utilizes heartbeats between ESX hosts in the cluster to check that they are functioning. When a host failure is detected, VMware HA automatically restarts affected virtual machines on other production servers, ensuring rapid recovery from failures. Once VMware HA is configured, it operates without dependencies on operating systems, applications, or physical hardware.
Use Case: Protect Virtual Machines from Server Failures
When running Web servers or databases that are critical to your business, VMware HA ensures they will be restarted immediately upon failure of their servers. Interruption to your business will be minimized as the virtual machine is restarted on another available server in your HA cluster.
Step 1: Turn on VMware HA on a cluster
VMware HA can only be turned on for a cluster of ESX hosts. Please ensure that you have followed the prior steps in creating a cluster of ESX hosts. Please also ensure that DNS is set up and working properly, including forward and reverse lookups, fully-qualified domain names (FQDN) and short names. Consult your network administrator for assistance in DNS configurations.
It is also recommended you set up alternate isolation response address (best practice).
- To enable VMware HA on your cluster, right-click the cluster and select Edit Settings. The cluster settings window should appear.
- Under Cluster Features of the cluster settings window, select Turn On VMware HA. Each ESX host in the cluster will now be configured for VMware HA. Please note that you will need cluster administrator permissions to edit the cluster settings.
Step 2: Set Admission Control and Additional VMware HA options
You may want to set additional VMware HA options to allow for admission control, monitoring and setting policies for your hosts and virtual machines. These can be configured under VMware HA in the cluster settings window. The following is a listing of these addition features.
• Disabling host monitoring will allow you to perform ESX host maintenance without triggering VMware HA into thinking the host has failed.
• Admission control allows you to control whether virtual machines should be restarted after host failures depending on if resources are available
elsewhere in the cluster. VMware HA uses one of three admission control policies:
1) tolerate some number of host failures,
2) specify a percentage of cluster resources or,
3) specify a designated failover host.
VM monitoring restarts virtual machines after their VMware Tools heartbeat is lost, even if their host has not failed. The monitoring sensitivity level can be set for each virtual machine.
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