Savings Plan vs On-Demand by Workload Type
Over-committing kills flexibility; under-committing wastes money. Per-workload analysis is the answer.
Why one rule is wrong
Stable workloads: commit deeply.
Variable workloads: commit shallowly + buffer with on-demand.
One-shot workloads: pure on-demand.
The wrong instrument for any of these wastes money.
Four workload categories
- Stable production: 90%+ committed.
- Variable production: 60-70% committed.
- Dev/staging: 30-50% committed.
- One-shot batch: 0% committed.
Math per category
Commitment cost = (steady-state usage × 0.7) typically. Buffer with on-demand for spike + safety.
Refresh quarterly; coverage drifts as workloads change.
On-demand buffer
Reserve 20-30% headroom on-demand. Keeps flexibility for surprise growth.
Without buffer, commitments lock you into yesterday’s capacity.
Antipatterns
- Same commitment for everything. Wastes flexibility.
- No buffer. Forced over-commit later.
- Annual review only. Drift wins.
What to do this week
Three moves. (1) Apply this lever to your highest-spend workload. (2) Measure the dollar impact for one month. (3) Roll the practice out to the next two services if the savings hold.