During a physical network reconfiguration, an ESXi host briefly lost connection to the management network. High Availability (HA) began powering off the virtual machines residing on the affected host to be restarted on an unaffected host in the cluster.
Which setting should the administrator configure to prevent this behavior in the future?
A. Host isolation response
B. Host monitoring
C. VM monitoring
D. Admission control
Correct Answer: B
Explanation/Reference:
Explanation:
If a host fails and its virtual machines need to be restarted, you can control the order in which this is done with the VM restart priority setting. You can also configure how vSphere HA responds if hosts lose management network connectivity with other hosts by using the host isolation response setting.
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 off virtual machines that are running on an isolated host and restart them on a nonisolated 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. When this occurs, the host executes its isolation response. The responses are: Leave powered on (the default), Power off then failover, and Shut down then failover. You can customize this property for individual virtual machines.
In this question, a temporary network outage occurred due to a physical network reconfiguration. We can prevent this happening by temporarily disabling host monitoring prior to performing maintenance such as a network reconfiguration.
Best Practices for Networking
The following network maintenance suggestions can help you avoid the accidental detection of failed hosts and network isolation because of dropped vSphere HA heartbeats.
When making changes to the networks that your clustered ESXi hosts are on, suspend the Host Monitoring feature.
Changing your network hardware or networking settings can interrupt the heartbeats that vSphere HA uses to detect host failures, and this might result in unwanted attempts to fail over virtual machines.
Incorrect Answers:
A: We have a cluster configured for HA. During the network outage, HA started doing its job of restarting VMs. This is what we would want to happen under normal circumstances. It also suggests that the host isolation response is configured correctly. We just want to temporarily disable HA while a performing network configuration to prevent VMs failing over unnecessarily. We can do this by suspending Host Monitoring as recommended by VMware. Therefore, this answer is incorrect.
C: It is not necessary to reconfigure VM monitoring (even if it is enabled). This would not prevent a host configured for HA from failing over in the event of network outage. Therefore, this answer is incorrect.
D: When you power on a virtual machine, the system checks the amount of CPU and memory resources that have not yet been reserved. Based on the available unreserved resources, the system determines whether it can guarantee the reservation for which the virtual machine is configured (if any). This process is called admission control. This is used to determine if a VM is restarted on a host. It does not prevent a host attempting to fail over its VMs to another host in the event of a network outage. Therefore, this answer is incorrect.
References:
http://pubs.vmware.com/vsphere-55/index.jsp#com.vmware.vsphere.avail.doc/GUID-FA8B166D-A5F5-47D3-840E-68996507A95B.html
http://pubs.vmware.com/vsphere-55/index.jsp#com.vmware.vsphere.avail.doc/GUID-B1906BCD-E538-4FFF-AAE9-5403FE253F38.html
Explanation/Reference:
Explanation:
If a host fails and its virtual machines need to be restarted, you can control the order in which this is done with the VM restart priority setting. You can also configure how vSphere HA responds if hosts lose management network connectivity with other hosts by using the host isolation response setting.
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 off virtual machines that are running on an isolated host and restart them on a nonisolated 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. When this occurs, the host executes its isolation response. The responses are: Leave powered on (the default), Power off then failover, and Shut down then failover. You can customize this property for individual virtual machines.
In this question, a temporary network outage occurred due to a physical network reconfiguration. We can prevent this happening by temporarily disabling host monitoring prior to performing maintenance such as a network reconfiguration.
Best Practices for Networking
The following network maintenance suggestions can help you avoid the accidental detection of failed hosts and network isolation because of dropped vSphere HA heartbeats.
When making changes to the networks that your clustered ESXi hosts are on, suspend the Host Monitoring feature.
Changing your network hardware or networking settings can interrupt the heartbeats that vSphere HA uses to detect host failures, and this might result in unwanted attempts to fail over virtual machines.
Incorrect Answers:
A: We have a cluster configured for HA. During the network outage, HA started doing its job of restarting VMs. This is what we would want to happen under normal circumstances. It also suggests that the host isolation response is configured correctly. We just want to temporarily disable HA while a performing network configuration to prevent VMs failing over unnecessarily. We can do this by suspending Host Monitoring as recommended by VMware. Therefore, this answer is incorrect.
C: It is not necessary to reconfigure VM monitoring (even if it is enabled). This would not prevent a host configured for HA from failing over in the event of network outage. Therefore, this answer is incorrect.
D: When you power on a virtual machine, the system checks the amount of CPU and memory resources that have not yet been reserved. Based on the available unreserved resources, the system determines whether it can guarantee the reservation for which the virtual machine is configured (if any). This process is called admission control. This is used to determine if a VM is restarted on a host. It does not prevent a host attempting to fail over its VMs to another host in the event of a network outage. Therefore, this answer is incorrect.
References:
http://pubs.vmware.com/vsphere-55/index.jsp#com.vmware.vsphere.avail.doc/GUID-FA8B166D-A5F5-47D3-840E-68996507A95B.html
http://pubs.vmware.com/vsphere-55/index.jsp#com.vmware.vsphere.avail.doc/GUID-B1906BCD-E538-4FFF-AAE9-5403FE253F38.html