# 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: ```bash systemctl stop pve-cluster corosync ``` Watch the Proxmox web console — the VM should automatically start on another node