Build a recovery-time budget for a redundant network path. Add failure detection, route convergence, state synchronization, and service recovery delays, then compare the sum with a target. The result shows both remaining margin and the largest delay component, helping teams focus testing and optimization on the part that dominates failover time.
A positive margin indicates that the staged estimate fits within the selected recovery target. A negative margin is the amount by which the target is missed.
This is a deterministic budget. Production recovery time also varies with packet loss, control-plane load, cold caches, health-check alignment, and dependency failures; validate percentiles through fault injection.
With a 5,000 ms target, 1,000 ms detection, 1,200 ms rerouting, 800 ms synchronization, and 500 ms service recovery, total failover time is 3,500 ms. The remaining margin is 1,500 ms.
No. This calculator budgets service interruption during failover, not steady-state request round-trip time.
Aggressive timeouts may interpret brief congestion or packet loss as a failure and trigger unnecessary failover.
Include DNS or client cache delay in rerouting when failover depends on clients resolving a new destination.
The estimated failover stages take longer than the selected recovery-time target.
Treat it as the first optimization candidate, then retest because another stage may become dominant.
| Variable | Meaning | Unit |
|---|---|---|
| T | Recovery-time objective | ms |
| D | Failure detection | ms |
| R | Route convergence | ms |
| S | State and service recovery | ms |