In the last VMware for Beginners article, we discussed about vMotion and DRS, and now we have our DRS enabled and our vMotion network, we can start configuring vSphere HA and Proactive HA.
VMware vSphere HA is one of the most important features inside vCenter and is a significant and extensive feature in your VMware environment. Since we always want to provide the most detailed information in our VMware for Beginners articles, we will divide the article into three parts. This is part one.
Table of Contents
- What is vSphere HA?
- How does it work?
- Key features:
- Type of vSphere HA host scenarios types:
- 1. Failure. A host stops functioning
- 2. Isolation. A host becomes network isolated
- 3. Partition. A host loses network connectivity with the primary host
VMware vSphere High Availability (HA) is a feature that protects virtual machines from host failures by restarting them on other available hosts in the Cluster.
vSphere HA is a vital component of the vSphere platform, providing cost-effective high availability for business-critical applications. In this blog post, we will explore what vSphere HA is, how it works, and some of its key benefits.
What will we discuss in this vSphere HA topic?
- What is vSphere HA
- How does it work
What is vSphere HA?
vSphere High Availability (HA) is a feature of the vSphere platform that protects your virtual machines from host failures. If a physical server in your Cluster goes down, vSphere HA automatically restarts the virtual machines on other hosts in the Cluster.
vSphere HA is transparent to users and requires no changes to your applications. It is easy to set up and requires no additional networking configuration (except the vMotion network to migrate VMs between ESXi hosts).
This ensures that your applications remain available in case of a host failure.
How does it work?
VMware vSphere High Availability (HA) is a data center feature that reduces downtime for applications and services in the event of a hardware or software failure. When a failure occurs, vSphere HA automatically restarts any affected virtual machines on alternative hosts. This ensures that your applications and services remain available even when individual components fail.
vSphere HA constantly monitors each virtual machine’s and host’s health in your Cluster. If a virtual machine or host fails, vSphere HA immediately detects the failure and starts the affected virtual machines on other hosts in the Cluster. This process is automatic and requires no administrator intervention.
When a cluster is configured with Host High Availability, hosts communicate with each other via a heartbeat. This periodic message tells the master host that the node or VM is running as expected. If it doesn’t detect the heartbeat signal from another host or VM, vSphere HA takes corrective actions such as restarting hosts and VMs.
In addition to providing high availability for individual virtual machines, vSphere HA can protect your entire application by restarting virtual machines in accordance with a pre-defined order. This ensures that critical components are always started first, followed by less important components. By starting virtual machines in this order, you can minimize downtime and ensure that your applications are always available.
vSphere HA is an essential data center feature that can help you avoid costly downtime for your applications and services. By automatically restarting affected virtual machines on alternative hosts, vSphere HA ensures that your applications remain available even when individual components fail.
Key features:
- Monitor VMware vSphere hosts and virtual machines to identify hardware or guest operating system failures
- vSphere HA is continuously monitoring if any of the ESXi hosts are down. If it detects an outage, HA restarts virtual machines on other vSphere hosts in the Cluster without any intervention necessary
- Virtual Machines automatically restart when VM Monitoring detects an operating system failure. This keeps applications up and running, which reduces downtime
Type of vSphere HA host scenarios types:
A VMware vSphere High Availability cluster’s primary host is responsible for monitoring secondary hosts for failures. Virtual machines running on the hosts may need to a failover, depending on the type of failure detected.
In a vSphere HA cluster, three types of host failure are detected:
Datastore Heartbeat and gateway ping monitor for host failure or isolation.
1. Failure. A host stops functioning
When an ESXi host fails, VM failover is triggered. All VMs from the failed ESXi host will migrate and restart on an available ESXi host.
In the following example, VMs 1 and 2 were migrated from the ESXi host to the next available ESXi host. All the VMs’ files are stored on a Shared Storage that all ESXi hosts have access to (HA requires this).
2. Isolation. A host becomes network isolated
When a host becomes isolated from the network, it can no longer communicate with other hosts in the Cluster.
This can happen for many reasons, including:
- The host has lost network connectivity
- The host has been manually isolated
- The host is in a network partition
If a host becomes isolated, vSphere HA ensures that any virtual machines running on the host are protected. If the host is part of a cluster with vSphere HA enabled, the other hosts in the Cluster continue to provide resources and services to the virtual machines on the isolated host.
3. Partition. A host loses network connectivity with the primary host
When this occurs, vSphere HA detects the partition and restarts any affected virtual machines on other hosts in the Cluster. This failover is transparent to users because the virtual machines are restarted on other hosts in the Cluster.
When a host loses network connectivity with the primary host, it automatically attempts to connect to a secondary host in the Cluster. If the host cannot connect to the secondary host, it restarts any virtual machines running on the primary host.
On host failures 2 and 3, if any of the hosts are not reachable with gateway ping, Datastore heartbeats, or VM Monitoring, VMs are restarted in the next available ESXi host.
Note: ESXi host agent or gateway cannot be reachable, but VMs can still be running and reachable. That is why it is essential to have also VM Monitoring in place. But for that, your VMs needs to have VMware Tools installed.
Read More:
VMware for Beginners: A Step-by-Step Guide to Learn VMware and Boost Your Career
VMware for Beginners – vSphere HA Configuration: Part 12(b)
VMware for Beginners – vSphere HA Configuration: Part 12(c)
VMware for Beginners – vMotion and DRS: Part 11
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