Vmware : vSphere High Availability (HA)

High Availability

Provides for the automatic restart of VMs if they are on a host that fails; minimizes server downtime.

This High availability is maintained by the heartbeats that are exchanged between hosts in an HA cluster. When the cluster determines that a host is isolated or has failed, it will follow the isolation response that you have configured.

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VMware Fault Domain Manager Master/Slave Relationship

There is only one FDMS host per Cluster and it is determined via election process. The host that has visibility to most datastores is going to become FDMS.

Responsibilities of FDMS:-

Monitors the state of other slave ESXi hosts

Monitors the state of all protected Virtual Machines in the cluster

Requirements for VMware High Availability

Cluster with HA Enabled

At least one Management Network per ESXi host

Shared storage

All ESXi host have access to all VM Networks

Enable High Availability

Right on Cluster that you have created and Select Edit Setting.

Once you Enable it, you will get access to additional options. Lets get start with vSphere HA.

Enable Host Monitoring allows the HA cluster to continuously monitor ESXi hosts within the cluster for heartbeat.If it doesn't receive the heartbeat then it will declare that host in isolation mode.

Admission Control

For more information click here

Admission Control Policy

For more information click here

Virtual Machine Options

VM Restart Priority:The default configuration in the cluster is Medium. If you leave the default setting, all VMs will have the same priority on restart. If there are some VMs that you want to have a greater priority ,you can change the restart priority on the specific VMs.

Host Isolation Response: This is the setting that determines what the host does with regard to VMs when the host is not receiving heartbeats on its management network. The options are to leave powered on, power off, or gracefully shut down the VMs.

VM Monitoring restarts individual virtual machines if their VMware Tools heartbeats are not received within a set time.By default VM monitoring is disabled. You can change it if you need.

When the master host in a HA cluster can not communicate with a slave host over the management network, the master host uses datastore heartbeating to determine whether the slave host has failed. If the slave host has stopped datastore heartbeating, it is considered to have failed and its virtual machines are restarted on other ESXi host.