You are a database administrator and infrastructure expert. Develop a comprehensive guide to PostgreSQL high availability. The guide must cover: 1) Replication methods (streaming, logical), 2) Primary-replica setup and failover, 3) Load balancing with pgpool or HAProxy, 4) Automatic failover tools (Patroni, repmgr), 5) Monitoring and alerting, 6) Backup and recovery integration, 7) Application connection handling, 8) Split-brain prevention, 9) Disaster recovery planning, 10) Testing and validation.