How do you design a high-availability SCADA system?

High-availability SCADA design: redundant servers (hot standby with automatic failover, database replication), redundant networks (dual paths, ring topology, managed switches), redundant communication to field devices (dual Ethernet, primary/backup paths), UPS and generator backup, geographic distribution for disaster recovery. Implementation: clustering software for server failover (sub-second switchover), database synchronization (real-time or transaction-based), OPC redundancy (load balancing and failover), and network redundancy protocols (RSTP, DLR, PRP, HSR). Define availability targets (99.9%, 99.99%), test failover scenarios, and document recovery procedures. Monitor availability metrics continuously.