How do you design high-availability controller architectures for critical processes?

High-availability controller design: redundancy modes (hot standby with automatic switchover, or active-active load sharing), synchronization (state transfer between redundant controllers, memory synchronization), switchover criteria (watchdog timeout, self-diagnostics, communication loss), bumpless transfer (outputs maintain value during switchover), independent failure paths (separate power, I/O buses, networks), and diagnostics (health monitoring, predictive failure). Implementation: configure synchronization parameters, test switchover under various failure scenarios, verify bumpless transfer on outputs, and establish maintenance procedures (online replacement, preventive switchover). Consider: TMR (triple modular redundancy) for highest availability, voting on outputs, and diversity to address common cause failures. Document failure modes and recovery procedures. Track switchover events for reliability analysis.