Glossary · System coordination, integration and orchestration
Active-standby redundancy
Also known as: active-passive redundancy, primary-backup redundancy, hot standby
German: Aktiv-Standby-Redundanz
In system architecture, active-standby redundancy is a redundancy scheme in which one unit performs the function while a second unit is kept ready and takes over only when the active unit fails. The standby may be hot (synchronized and running), warm or cold.
- System integration
In one sentence
In active-standby redundancy one unit works while a second waits ready and takes over by failover when the active unit fails.
Example
A redundant PLC pair runs the kiln control on the primary CPU; the backup CPU tracks its data and takes control within one cycle when the primary faults.
How it applies
- Engineering: Decide how the standby learns about state changes (hot, warm or cold standby), how it detects failure of the active unit, typically by Heartbeat monitoring, and how long the switchover may take for the process.
- Maintenance: Standby units age silently. Plan periodic switchover tests so that a defective backup is found before it is needed.
- Documentation: Operator and service manuals should explain how to read the active/standby status, how to force a switchover for maintenance and what the plant does during the switchover. State the switchover time only if it has been verified.
Active-standby vs. active-active redundancy
Active-active redundancy shares the load across all nodes. Active-standby keeps spare capacity idle, which makes state handling simpler but introduces a Failover event that must be detected, executed and tested.