HA in VMware: Simplified 101

Nicholas Samuel • Last Modified: December 29th, 2022

ha in vmware: FI

Virtual Machines are very common in companies today, especially those that use multiple applications. They enable businesses to install and run software and applications in a separate environment from the rest of the system. This allows for more efficient resource utilization. Downtimes do occur when running virtual machines. These are usually the result of unplanned events such as a network outage, a power outage, or a system crash.

Planned events such as upgrades and maintenance can also result in downtime. During downtimes, it means that the company employees cannot access the applications that run in the virtual environments.

Customers may be unable to interact with the company during downtimes. Companies should devise methods to reduce application downtimes to maintain business continuity. HA in VMware is the solution. It restarts failed virtual machines on alternative host servers to reduce application downtime. This is done automatically without human interference.

This article talks about HA in VMware in detail.  It also gives an overview of VMware and its key features.

Table of Contents

What is VMware?

VMware, Inc., based in California, is a cloud computing and virtualization technology company. VMware was the first company to successfully virtualize the x86 architecture in a commercial setting.

VMware’s desktop software runs on Microsoft Windows, Linux, and macOS, while VMware ESXi, the company’s enterprise software hypervisor for servers, is a bare-metal hypervisor that runs directly on server hardware without the need for a separate underlying operating system.

The software company’s first product, VMware Workstation, was released in 2005. Users can create and run virtual machines (VMs) on a single Windows or Linux desktop or laptop. Those virtual machines run alongside the physical machine at the same time. Each virtual machine (VM) has its operating system (OS), such as Windows or Linux.

VMware provides a wide range of digital solutions that power apps, services, and experiences that help businesses provide excellent customer service and empower their employees.
VMware makes it easier for businesses to transform into digital enterprises that provide better customer experiences and enable employees to do their best work. App Modernization, Cloud, Networking & Security, and Digital Workspace are just a few of the areas where your software can help.

Storage and availability products from VMware are divided into two categories:

  • VMware vSAN (formerly VMware Virtual SAN) is a software-defined storage solution that is built into VMware’s ESXi hypervisor. To create a hyper-converged infrastructure, the vSphere and vSAN software are installed on industry-standard x86 servers (or HCI). However, to put one into production, network operators will need servers from the HCL (Hardware Compatibility List). In March of 2014, the first version, 5.5, was released. In April of 2017, the 6th generation, version 6.6, was launched. Native data at rest encryption, local protection for stretched clusters, analytics, and improved solid-state drive performance are among the new features available in VMware vSAN 6.6. Users now have improved monitoring tools and new workflows, and VMware 6.7 is closer to feature parity. The architecture of the vCenter Server Appliance is evolving towards a simple deployment method.
  • Using Policy-Based Management, VMware Site Recovery Manager (SRM) automates the failover and failback of virtual machines to and from a secondary site.

Key Features of VMware

  • Easy Installation: Installs like a program, with a wizard-driven installation and virtual machine creation process.
  • Seamless Migration to vSphere: Use the free web-based service to safeguard your investment. VMware To migrate your virtual machines to VMware vSphere in a seamless manner, go here.
  • Hardware Support: Runs on any standard x86 hardware, including virtualization-assisted Intel and AMD systems. Supports Virtual SMP on two processors, allowing a single virtual machine to span multiple physical processors.
  • Operating System Support: Windows Server 2008, Windows Vista Business Edition and Ultimate Edition (guest only), Red Hat Enterprise Linux 5, and Ubuntu 8.04 are among the operating systems supported by any host-based virtualization platform currently available.
  • 64-bit Operating System Support: To enable more scalable and high-performing computing solutions, use 64-bit guest operating systems on 64-bit hardware. Server 2 also runs on 64-bit Linux host operating systems natively.
  • VMware Infrastructure (VI) Web Access Management Interface: The VI Web Access management interface makes management easy, flexible, secure, intuitive, and productive. In addition, the Virtual Appliance Marketplace offers thousands of pre-built, pre-configured, ready-to-run enterprise applications packaged with an operating system inside a virtual machine.
  • Independent Virtual Machine Console: You can access your virtual machine consoles without using the VI Web Access management interface when you use the VMware Remote Console.
  • More Scalable Virtual Machines: Support for up to 8 GB of RAM and up to 10 virtual network interface cards per virtual machine, plus the ability to add new SCSI hard discs and controllers to an existing virtual machine.
  • Volume Shadow Copy Service (VSS): Maintain the data integrity of the applications running inside the virtual machine by properly backing up the state of Windows virtual machines when using the snapshot feature.
  • Support for Virtual Machine Interface (VMI): This feature allows transparent paravirtualization, which allows a single binary version of the operating system to run on native hardware or in paravirtualized mode to improve performance in specific Linux environments.
  • Virtual Machine Communication Interface (VMCI): Fast and efficient communication between a virtual machine and the host operating system, as well as between two or more virtual machines on the same host.

What is VMware vSphere?

VMware is a major player in the information technology industry, with decades of experience in providing virtualization solutions to industry professionals. vSphere is an advanced server virtualization application that provides users with a centralized management platform for their virtual machines (VMs).

When it was first released as a suite of virtualization products in the early 2000s, vSphere was known as VMware Infrastructure. It has gone through several iterations and a name change since then, with the most recent version, vSphere 7.0. ESXi and vCenter Server are the two core components of vSphere in this iteration.

VMware vSphere transforms data centers into simplified cloud computing infrastructures, allowing IT organizations to provide flexible and reliable IT services.

VMware ESXiTM and VMware vCenter Server are the two main components of vSphere. The hypervisor ESXi is used to create and run virtual machines. vCenter Server is a service that acts as a central administrator for network-connected ESXi hosts. You can pool and manage the resources of multiple hosts with vCenter Server. You can monitor and manage your physical and virtual infrastructure with vCenter Server.

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What is HA in VMware?

HA in VMware(VMware High Availability) is a VMware vSphere utility feature that eliminates the need for dedicated standby software or hardware in a virtual computing environment. HA in VMware can maximize uptime or availability across virtualized infrastructure by eliminating planned downtimes during times of upgrade and maintenance or unplanned downtimes that result from unexpected events. This is achieved by monitoring virtual machines and the hosts on which they run to automatically restart failed virtual machines on other vSphere hosts in case of a server failure and automatically restarting virtual machines in case of operating system failure. 

With HA in VMware, companies can protect applications without another failover option. Any application running on a virtual machine will have high availability as a result of this. High-availability solutions are typically complex and costly, and they are only used for mission-critical applications.

HA in VMware is a low-cost high-availability solution for software applications that were previously unprotected. It also helps companies establish a reliable “first line of defense” for their entire IT environment. Whereas most high-availability solutions are meant for specific software applications, HA in VMware is meant for the entire IT environment. It provides basic failover for any app at the minimum management and cost overhead. This ensures a smooth flow of operations in an organization even during times of disaster. Thus, any organization in need of ensuring the continuity of operations should consider using HA VMware. 

Key Features of HA in VMware

The following are the key features of HA in VMware:

  • Ability to Detect Server Failures Automatically: HA in VMware automates the process of monitoring physical servers for availability. It detects server failure automatically and restarts the virtual machine without human intervention, meaning that little human effort is required to run and maintain it. 
  • Resource Checks: HA ensures that capacity is available to restart the virtual machines affected by server failure. It keeps on monitoring capacity utilization and reserves spare capacity for restarting virtual machines. Thus, there are always available resources for restarting failed virtual machines. 
  • Automatically Restarts Virtual Machines: HA safeguards applications by automatically restarting them on a different physical server in the resource pool.
  • Intelligent Choice of Servers: Companies can use it with VMware Distributed Resource Scheduler (DRS) to automate the optimal placement of virtual machines that are restarted after a server failure. This can help keep them running for long. 

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How does HA in VMware work?

HA in VMware uses a fault-tolerant domain manager agent to monitor the availability of hosts and restart any failed virtual machines. When setting up HA in VMware, the administrator defines a group of servers to be used as the high-availability cluster. After that, the fault domain manager will run on all hosts in the cluster. One of the hosts within the cluster is made the master, and the other hosts become slaves. The master host continues to communicate with the vCenter server while monitoring signals from the other hosts in the cluster. 

The hosts running within the HA in the VMware cluster communicate by sending a periodic message which indicates whether they are running. This message is known as a heartbeat.  If the master host does not receive a heartbeat signal from any of the cluster’s hosts, it alerts vSphere HA to take action. 

The type of action to be taken depends on the type of failure as well as user preference. If the VMware on which the host server runs fails, HA in VMware will restart the VM on the original host. If the entire host fails, the utility will restart all the affected VMs on the other hosts within the cluster. 

The HA is also allowed to restart virtual machines if a host continues running but loses a network connection to the other hosts within the cluster. The reason is that a network failure can lead to the unavailability of a host. To determine whether a network-segregated host is still running, the master can check if the host is communicating with network-connected data stores. 

How to Setup HA in VMware?

To set up HA VMware, follow the steps given below:

  • Step 1: Create a cluster from the vSphere web client under the “Create a Cluster” option. 
  • Step 2: Choose ESXi hosts and shared storage to take part in the cluster. 

Although most organizations maintain larger clusters capable of pulling many resources to accommodate multiple failures, HA clusters should have at least two hosts.

The admin can then turn on the HA feature from the web client by clicking through Manage -> Settings -> vSphere HA. 

A user can alter the vSphere HA configuration settings and preferences using the vSphere web client. 

HA in VMware: Requirements and Best Practices

Administrators have control over several HA settings. For example, how long a host or virtual machine can be unavailable before HA tries to restart it, with the default value being 120 seconds. The admin can also set the order in which the virtual machines within the cluster will be restarted. In most cases, priority is given to VMs running mission-critical applications. 

A company can also come up with affinity and anti-affinity rules to govern the placement of virtual machines. These rules prevent particular VMs from restarting on selected servers or servers hosting other specified VMs. They are useful because they ensure CPU-intensive virtual machines don’t start on the same host or high-priority applications don’t run on the same host, which can create a single point of failure. 

That is how HA in VMware works. 


This article explains that Companies can use virtual machines to set up and run applications that are isolated from the rest of the system, allowing for more efficient resource utilization.

When using virtual machines, downtimes do occur as a result of planned system upgrades as well as from the occurrence of unexpected events. 

HA in VMware maximizes uptime or availability across virtualized infrastructure by eliminating planned and unplanned downtimes. 

When a server fails, it monitors virtual machines and the hosts on which they run, and restarts failed virtual machines on other vSphere hosts. It also restarts virtual machines automatically in case of operating system failure. 

HA in VMware is implemented using a master-slave architecture, in which slaves send periodic message signals (heartbeats) to the master to inform it that they are operational. Action is taken when the master doesn’t receive a message signal from a host. 

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