Capacity Forecasting

Capacity forecasting

Running out of capacity is a predictable incident, which makes it an avoidable one. Forecasting converts a future outage into a scheduled piece of work.

Method

1. Identify the binding constraint. Which resource exhausts first, since forecasting the wrong one produces confident wrong plans (see capacity-planning).
2. Project from real growth, not from targets. Historical trend with its variance, because business plans are optimistic and capacity plans should not be.
3. Plan to a threshold, not to the limit. Trigger the increase at a utilisation level that leaves time to act.
4. Include the lead time. Procurement, provisioning, and migration take time that must be subtracted from the runway.
5. Account for headroom for spikes. Steady-state capacity that cannot absorb a peak is not adequate (see load-shedding).
6. Model step changes separately. A launch or a large customer moves demand discontinuously, and trend extrapolation misses it.
7. Review the forecast against actuals. A forecast never compared to what happened does not improve.

Boundaries

Forecasts assume patterns continue and miss discontinuities. Elastic infrastructure reduces but does not remove the problem, since quotas and cost ceilings still bind. Over-provisioning is a real cost, so the trade needs stating (see cloud-cost-optimization).