January 24, 2017
VMware Cluster. HA Configuration
In the previous post, we looked at the first key VMware vSphere cluster technology – DRS. The other key VMware cluster technology is VMware HA or high availability.
High Availability or the ability of a virtual environment to withstand host failures is one of the important reasons that you would choose to deploy a VMware vCenter cluster as opposed to a standalone VMware ESXi host. When HA is running on a VMware cluster, an agent is installed on each host participating in the cluster. Each host agent communicates with each other and monitors the reachability of the hosts in the cluster via heartbeats. If a 15-second interval passes without the receipt of heartbeats from a particular host and pings also fail to the host, the host is declared as failed. The VMs that are running on the compute/memory resources of the failed host are failed over and restarted on a healthy host.
New in vSphere 6.5, HA can monitor the hardware health of your hosts to proactively move VMs off hosts that have hardware issues. In vSphere 6.5, there are also restart priorities and orchestration incorporated with HA so designated VMs are brought online before others in the event of a failover.
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VMware Cluster. Requirements
There are a few requirements from VMware when considering creating a VMware cluster with HA enabled. They include the following:
- Hosts in the HA cluster must be licensed for vSphere HA
- Two hosts are required to enable HA
- Static IP addresses configured on each host is the best practice
- You need at least one management network that is common across the hosts
- In order for VMs to run across all hosts in case they are moved to different hosts in the cluster, the hosts need to have the same networks and datastores configured
- Shared storage is required for HA
- VMware tools need to be running on VMs being monitoring in HA
HA Configuration
The vSphere Availability settings can actually be accessed from the same screen that opens to turn on DRS. Again, there is a simple checkbox to Turn ON vSphere HA. Notice also, there is the aforementioned Proactive HA that can decide based on vendor providers whether or not there is a hardware failure on a particular host and migrate VMs off based on host health.
As with DRS, we can drill down into the settings of vSphere HA and customize the behavior.
We can select the automation level, remediation settings, etc. for VMs and hosts once a failure has occurred.
Admission control settings ensure failover capacity.
The heartbeat datastores provide a secondary way to monitor hosts if a management network has failed.
Finally, we can configure advanced configuration settings for the HA settings if desired.
As with DRS, once we click OK, the VMware cluster is reconfigured for the HA settings that were configured above.
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Thoughts
The real power, resiliency, and scalability of the VMware vSphere ESXi platform is unlocked once the vCenter Server is provisioned and the ESXi hosts are added to a vSphere ESXi cluster. With features such as DRS and HA, vSphere is able to effectively provide protection against host failures as well as balance and schedule resources for VMs. Both DRS and HA are even more powerful with vSphere 6.5 as VMware has added in more proactive and intelligent monitoring and insight to both of these cluster features allowing them to be agile and proactive.
