Troubleshoot Issue: vCenter Is Unable to Find a Master HA Agent

To navigate this challenge, this article dives deep into the crucial importance of HA in virtualized environments and uncovers the common causes behind vCenter's inability to locate a master HA agent. Moreover, it guides you through the process of configuring vCenter HA with the vSphere client, empowering you to take proactive steps to bolster your infrastructure's resilience.


By Zelia / Updated on October 30, 2023

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Importance of high availability in virtualized environments

High availability is the backbone of a well-functioning virtualized infrastructure. It ensures that applications and services remain accessible even in the face of hardware failures or other disruptive events. The HA feature in vCenter provides a safeguard against downtime by enabling automatic failover and redundancy for critical vCenter components. This is particularly vital for organizations relying on virtualized environments to run their mission-critical applications.


Common Causes of vCenter is unable to find a master HA agent

When vCenter cannot locate a master HA agent, it can disrupt the HA configuration and impact the overall availability of the virtualized environment. Some common causes of “vCenter server is unable to find a master vSphere HA agent” include:

  • Network Connectivity Issues: Poor network connectivity can prevent vCenter from communicating with the HA agents on ESXi hosts, leading to a failure in detecting the master agent.
  • ESXi Host Problems: Issues with the ESXi hosts, such as hardware failures, misconfigurations, or resource constraints, can affect the operation of the HA agents.
  • vCenter Server Issues: Problems with the vCenter server itself, including resource depletion or software glitches, can lead to the inability to identify a master HA agent.

How to configure vCenter HA with the vSphere client

Configuring vCenter High Availability (vCenter HA) with the vSphere Client is a crucial step in ensuring the resilience and availability of your vCenter Server. If you meet “vSphere HA agent on this host is disabled”, here are the steps to configure vCenter HA using the vSphere Client:

✍ Prerequisites
● Deploy vCenter Server that you want to use as the initial Active node
● Verify that your environment meets the following requirements
● Set up the infrastructure for the vCenter HA network
● Determine which static IP addresses to use for the two vCenter Server nodes that will become the Passive node and Witness node

1. Log in to the Active node with the vSphere Client.

2. Within the inventory, choose the vCenter Server object and access the Configure tab.


3. Select vCenter HA under settings.

4. Initiate the setup wizard by clicking on the Set Up vCenter HA button.

  • If the vCenter server is self-managed, you'll proceed to step 7, specifically to the Resource settings page.
  • If your vCenter server is managed by another vCenter server in the same SSO domain, move to step 7.
  • In case your vCenter server is managed by another vCenter server in a different SSO domain, input the location and credential details of the managing vCenter server.

5. Access the Management vCenter Server credentials. Provide the FQDN or IP address of the Management vCenter server, the Single Sign-On username, and the password. Click Next. If you lack the Single Sign-On administrator credentials, select the second option and proceed with Next.

6. You might encounter a Certificate warning. Examine the SHA1 thumbprint and select Yes to continue.

7. In the Resource settings section, begin by selecting the vCenter HA network for the active node from the provided dropdown menu.

Note: The network selector becomes hidden after creating NIC2/eth1.

8. Choose to create clones automatically for the Passive and Witness nodes by checking the designated checkbox.

Note: If not selected, manual clone creation for these nodes will be necessary after clicking Finish.

9. For the Passive node, click Edit and perform the following actions:

  • Specify a unique name and target location.
  • Select the destination compute resource for the operation.
  • Select the datastore in which to store the configuration and disk files.
  • Select virtual machine Management (NIC 0) and vCenter HA (NIC 1) networks.
  • Errors or compatibility warnings may be displayed if issues arise with your selections.
  • Review your selections and click Finish.

10. For the Witness node, click Edit and complete these tasks:

  • Specify a unique name and target location.
  • Select the destination compute resource for the operation.
  • Select the datastore in which to store the configuration and disk files.
  • Select vCenter HA (NIC 1) network.
  • If there are issues with your selections, errors or compatibility warnings are displayed.
  • Review your selections and click Finish.


11. In the IP settings section, choose the IP version from the provided drop-down menu.

12. Input the IPv4 address (NIC 1) and the Subnet mask or prefix length information for the Active, Passive, and Witness nodes. Customizing these settings is optional. By default, the management network settings of the Active node are applied. Once configured, click Finish.


Regular backup for preventing vCenter HA agent issues

Regular virtual machines backups are a fundamental component of maintaining the availability and data integrity of your virtualized environment, especially when working with vCenter HA. AOMEI Cyber Backup is a capable VMware backup solution that can play a crucial role in preventing vCenter HA agent issues. Here're some benefits by using AOMEI Cyber Backup for regular VM backups:

◆Agentless Backup: Create complete and independent image-level backup for VMware ESXi and Hyper-V VMs without installing any agent.
◆Multiple VM Backup: Batch backup large numbers of VMs managed by vCenter Server, or multiple VMs on a standalone ESXi host.
◆Multiple Storage Destinations: Backup to a local drive, or network destinations like NAS.
◆Automated Execution: Create backup schedules to automate backups daily, weekly, or monthly.
◆Restore Entire VM: Restore instant available VMs from any selected restore points to an original or new location.

AOMEI Cyber Backup supports various versions including ESXi 6.0 and later versions. You can click the button below to enjoy the 30-day free trial:

Download Free TrialVMware ESXi & Hyper-V
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Steps to use AOMEI Cyber Backup for regular VM protection

1. Bind Devices: Access to AOMEI Cyber Backup web client, navigate to Source Device >> VMware >> + Add VMware Device to Add vCenter or Standalone ESXi host. And then click >> Bind Device.


2. Create Backup Task: Navigate to Backup Task >> + Create New Task >> Backup Type >> VMware ESXi Backup and set Task Name, Device, Target, Schedule, and Cleanup as needed.

  • Schedule (optional): Perform full, differential, or incremental backup, and automate execution according to the frequency you specified.


  • Device: Batch select large numbers of VMs managed by vCenter Server for centralized backup.


  • Cleanup (optional): Automatically delete the old backup copies that exceed the retention period you specified.


3. Run Backup: Click Start Backup and select Add the schedule and start backup now, or Add the schedule only.


4. Restore Task: When restoring, you can also Restore to new location to create a new VM in the same or another datastore/host directly from the backup, saving the trouble of re-configuring the new VM.



High availability is the linchpin of a well-structured virtualized environment. When vCenter struggles to find the master HA agent, it can jeopardize the resilience of your infrastructure. Understanding the common causes of “vCenter is unable to find a master HA agent” and proactively configuring vCenter HA using the vSphere client can mitigate such problems.

Additionally, incorporating regular virtual machine backups through software like AOMEI Cyber Backup ensures that your virtualized environment remains stable, even in the face of unexpected challenges. By addressing these key aspects, you can bolster the reliability and availability of your virtualized infrastructure, ensuring that it continues to meet your organization's needs without unnecessary disruptions.

Zelia · Editor
Zelia is an editor from AOMEI Technology.She mainly writes articles about virtual machine. Writing is one of her hobbies and she wants her articles to be seen by more people. In her spare time, she likes to draw and listen to music, and it is a pleasure for her to focus on her own world.