High availability clustering eliminates single points of failure by running services across multiple nodes with automatic failover. Linux-HA's Heartbeat daemon provides a proven foundation for building HA clusters that maintain service availability even when individual servers fail.
Heartbeat Configuration and Resource Management
Heartbeat monitors the health of cluster nodes by exchanging UDP packets over a dedicated heartbeat network link. When a node fails to respond within the configured timeout, the surviving node takes ownership of the shared resources, including virtual IP addresses and application services. Use a dedicated crossover cable or VLAN for heartbeat traffic to prevent false failovers caused by network congestion.
Shared storage is typically required for stateful services. A SAN or DRBD (Distributed Replicated Block Device) provides the shared data layer that both nodes can access. DRBD is particularly attractive as it replicates data over the network, eliminating the need for expensive shared storage hardware while providing synchronous replication for data consistency.
Test failover regularly by simulating various failure scenarios including network failure, process crash, and complete node shutdown. Document the expected failover time and verify that it meets your service level objectives. Automated failback is convenient but should be used cautiously; manual failback after investigating the root cause of the original failure is often safer.