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 VMware HA - Quick View for Interviews


✅ What is VMware HA?


VMware High Availability (HA) is a feature in vSphere that automatically restarts virtual machines (VMs) on another available host in case of a failure, ensuring minimal downtime.


✅ How Does VMware HA Work?


1 Cluster Configuration - HA is enabled at the cluster level in vSphere.


2 Host Monitoring - Each ESXi host communicates via HA heartbeats.


3 Failure Detection - If a host fails, HA identifies the issue and restarts affected VMs on another host.


4 Resource Allocation - HA ensures sufficient resources are available for failover using admission control policies.


✅ HA Primary Node Election Process


When HA is enabled, one ESXi host is elected as the Primary Node.


All other hosts act as Secondary Nodes.


The primary node is responsible for monitoring cluster health and coordinating VM restarts.


If the primary host fails, a new primary is elected from the remaining hosts.


✅HA Activation Scenarios


1 Host Failure - The ESXi host goes offline, and VMs restart on another host.


2 Network Isolation - The host loses network connectivity but remains powered on. HA restarts VMs on a healthy host.


3 APD (All Paths Down) - The host loses access to shared storage temporarily. HA waits before deciding on a failover.


4 PDL (Permanent Device Loss) - The host


permanently loses access to storage. HA immediately restarts affected VMs on another host.


✅ HA Communication & Heartbeats


HA uses the Management Network for heartbeats.


Datastore Heartbeats are used as a secondary check if network heartbeats fail.


HA detects failures based on heartbeat loss and triggers VM restarts accordingly.


πŸ“Œ Key VMware HA Ports


UDP 8182 - Used for HA agent communication.


TCP 443- Used for vSphere Client to vCenter communication.


UDP 902 Used for host management.

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