6.5.1

If a master host cannot communicate directly with the agent on a subordinate host, the subordinate host
does not respond to ICMP pings. If the agent is not issuing heartbeats, it is viewed as failed. The host's
virtual machines are restarted on alternate hosts. If such a subordinate host is exchanging heartbeats with a
datastore, the master host assumes that the subordinate host is in a network partition or is network isolated.
So, the master host continues to monitor the host and its virtual machines. See “Network Partitions,” on
page 17.
Host network isolation occurs when a host is still running, but it can no longer observe trac from vSphere
HA agents on the management network. If a host stops observing this trac, it aempts to ping the cluster
isolation addresses. If this pinging also fails, the host declares that it is isolated from the network.
The master host monitors the virtual machines that are running on an isolated host. If the master host
observes that the VMs power o, and the master host is responsible for the VMs, it restarts them.
N If you ensure that the network infrastructure is suciently redundant and that at least one network
path is always available, host network isolation is less likely to occur.
Proactive HA Failures
A Proactive HA failure occurs when a host component fails, which results in a loss of redundancy or a
noncatastrophic failure. However, the functional behavior of the VMs residing on the host is not yet aected.
For example, if a power supply on the host fails, but other power supplies are available, that is a Proactive
HA failure.
If a Proactive HA failure occurs, you can automate the remediation action taken in the vSphere Availability
section of the vSphere Web Client. The VMs on the aected host can be evacuated to other hosts and the
host is either placed in Quarantine mode or Maintenance mode.
N Your cluster must use vSphere DRS for the Proactive HA failure monitoring to work.
Determining Responses to Host Issues
If a host fails and its virtual machines must be restarted, you can control the order in which the virtual
machines are restarted with the VM restart priority seing. You can also congure how vSphere HA
responds if hosts lose management network connectivity with other hosts by using the host isolation
response seing. Other factors are also considered when vSphere HA restarts a virtual machine after a
failure.
The following seings apply to all virtual machines in the cluster in the case of a host failure or isolation.
You can also congure exceptions for specic virtual machines. See “Customize an Individual Virtual
Machine,” on page 37.
Host Isolation Response
Host isolation response determines what happens when a host in a vSphere HA cluster loses its
management network connections, but continues to run. You can use the isolation response to have vSphere
HA power o virtual machines that are running on an isolated host and restart them on a non-isolated host.
Host isolation responses require that Host Monitoring Status is enabled. If Host Monitoring Status is
disabled, host isolation responses are also suspended. A host determines that it is isolated when it is unable
to communicate with the agents running on the other hosts, and it is unable to ping its isolation addresses.
The host then executes its isolation response. The responses are Power o and restart VMs or Shutdown and
restart VMs. You can customize this property for individual virtual machines.
N If a virtual machine has a restart priority seing of Disabled, no host isolation response is made.
Chapter 2 Creating and Using vSphere HA Clusters
VMware, Inc. 13