A single server is a single point of failure — if it goes down, the service becomes unavailable. Unplanned downtime leads to revenue loss, user trust erosion, and SLA violations.
Active-passive failover uses a standby server that takes over if the active server fails, with heartbeat monitoring detecting failure and triggering the switch.
- The active server handles all production traffic while the passive server remains idle.
- Heartbeat signals are sent between the active and passive servers at regular intervals.
- If the passive server stops receiving heartbeats, it assumes the active has failed.
- The passive server takes over the active server’s IP address (via IP takeover or virtual IP).
- The passive resumes service from the point the active left off (with shared storage).
- Downtime depends on the standby type: hot standby (minutes) vs cold standby (hours).
- Passive server sits on standby, handling zero traffic during normal operation
- Only the active server handles client requests
- Heartbeat-based failure detection triggers automatic failover
- Also called master-slave failover
- Failover time varies by standby type: hot (minutes) vs cold (hours)
- Contrasts with: Active-Active Failover — passive standby vs both serving traffic
- Related: Availability Nines — failover improves uptime percentage
- Related: Layer 4 Load Balancing — load balancers orchestrate failover routing
- Related: Horizontal Scaling — adding passive nodes is a scaling concern
- Split-brain scenario: both servers think the other is dead and both become active, causing data corruption
- Heartbeat network itself can be a single point of failure — redundant heartbeat links recommended
- Stateful services (in-memory sessions) are lost on failover unless backed by shared storage