Autoscaling Controller · View 21 of 37 · 4 · Runtime
The decision
- Hysteresis, sustain windows and delta rate limits — timers and bands, not a control law.
- Chosen for explainability: an operator at 3am can reason about "it waited six intervals" and cannot reason about a clamped integral term.
- A PI controller with a clamped integral is kept as an alternative policy form for phase 3, for targets whose plant delay is stable enough to tune against.
Numbers, all stated assumptions
- Dead band 15% of setpoint. Sustain 2 intervals out, 6 in.
- Rate limit +100% growth, -10% reduction per 60 s window.
- Oscillation freeze at 3 direction reversals in 15 minutes, naming the signal that reversed.
- No target loses more than 10% of capacity in any 60 s window.
Why asymmetric
- Being late to add capacity costs latency. Being wrong to remove it costs availability.
- Scale-in is suppressed entirely while capacity added in the last cooldown window is still becoming serving, so the loop never reacts to its own unfinished actuation.
