vSphere HA Architecture & FDM (VIB) Agent purpose running on ESXi Hosts

Products

• VMware vSphere ESXi

Issue/Introduction

• This article explains the purpose of the FDM agent VIB that is installed in the ESXi host

Environment

• ESXi 8.x 
• VCF 9.0

Resolution

• The below is the Architecture Diagram of vSphere HA feature on the vCenter 
  
  

What are the functions of the FDM VIB

• One FDM VIB per ESXi host
  FDMs elects a Primary FDM and all other ESXi Hosts become its Secondary nodes
  
  
• Primary Node
  Monitors host and VM availability
  Restart VMs on failure
  Reports state to VC via property updates
  
  
• Primary Node is elected when
  vSphere HA is enabled or when HA is reconfigured on Primary host
  Primary host fails, becomes partitioned, or isolated
  Hostd restarts of the FDM crashes on the Primary’s host
  A management network partition occurs
  
  
• Secondary Node
  Restart VMs when directed to do so by a Primary
  Report to Primary VM changes (e.g., reservation and power state)
  Report events to Primary
  
  
• Primary & Secondary Nodes
  Track VMs that are registered to its host
  Implement the VM/App Monitoring feature
  Record events that detail actions taken by the FDM
  Restart VMs following a failure
  
  
• FDM agents communicate using the management network
  
  
• Datastores are used as backup communication channel
  
  
• If the FDM VIB is removed or missing from an ESXi host, vSphere HA agent communication within the cluster is disrupted
  As a result, HA will not fail over virtual machines from that host because the FDM agent is not running

Additional Information

Tech Docs - vSphere HA