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High Availability

High Availability (HA) ensures that critical VMs are automatically restarted on another node if the node they are running on fails.

Prerequisites:

  • A working cluster with at least 3 nodes
  • Shared storage accessible by all nodes (so the VM disk can be accessed after failover)
  • The HA manager service must be running on all nodes

Note: HA requires a quorum (majority of nodes must be online). With 3 nodes, you can tolerate 1 node failure. With 2 nodes, there is no quorum and HA will not function.

 

Enabling HA for a VM

  1. Go to Datacenter > HA
  2. Click Add under Resources
  3. Select the VM ID you want to protect
  4. Set the HA State:
        • Started — HA will always try to keep this VM running
        • Stopped — HA will manage the VM but leave it stopped
        • Disabled — HA does not manage this VM
  5. Set Max Restart — how many times to try restarting on the same node before migrating
  6. Set Max Relocate — how many nodes to try before giving up
  7. Click Add

 

HA Groups

HA groups define which nodes are preferred or required for specific VMs.

  1. Datacenter > HA > Groups > Add
  2. Name the group and select nodes
  3. Set priority (higher = preferred) for each node
  4. Assign a VM to the group in HA Resources

 

Testing High Availability

  1. Start an HA-protected VM on one node
  2. Simulate a node failure by powering off that node or running:
systemctl stop pve-cluster corosync


Watch the Proxmox web console — the VM should automatically start on another node

 

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