Practical guide
Avoid unused Compute Engine commitment spend
Measure committed use discount utilization, account for eligible usage, and size a Compute Engine commitment from the lowest reliable baseline.
Updated · Sources checked
Utilization is the cost-control metric
Commitment utilization asks how much of the discounted obligation is matched by eligible use. A high nominal discount does not help when workloads disappear, move regions, change machine family, or become ineligible. Google applies commitments hourly, so monthly averages can mask overnight or weekend gaps.
Imagine a commitment worth 10 eligible units per hour. If usage is 10 units for 12 hours and 2 units for 12 hours, daily eligible consumption is 144 unit-hours while the commitment requires 240 unit-hours. Utilization is 144 ÷ 240 = 60%. A monthly spend chart that only shows total usage may hide that recurring gap; calculate at the same hourly granularity as commitment application.
Separate stable and variable demand
Build an hourly series for each eligible resource or spend category. Mark workloads that are scheduled, seasonal, migrating, or likely to be replaced. The smallest repeatedly observed baseline is a better starting point than the mean. A workload that autoscale-to-zero is not suitable for an always-on commitment merely because its monthly peak is high.
For compute-flexible CUDs, confirm which eligible Compute Engine, GKE, and Cloud Run charges share coverage. For resource-based CUDs, confirm regional resource quantities. A reservation is a separate capacity decision, and does not repair a commitment that has no matching use.
Review after purchase
Monitor commitment coverage and utilization in billing reports. Investigate a sustained drop promptly: a new region, a change from a supported machine type, or a deployment schedule can be the cause. Keep a dated record of the measured baseline and renewal assumption so a one-time launch month does not become a three-year forecast.
Test the range in the Compute Engine Committed Use Discount Calculator. Use the Compute Engine Cost Calculator to price the uncovered or variable remainder.
FAQ
Is 100% utilization required?
No, but utilization must leave enough savings after unused obligation to justify the commitment and its term risk.
Can sustained-use discounts be added to CUD savings?
No. Google documents discount types as mutually exclusive for eligible resources.
Official sources
- https://cloud.google.com/compute/docs/instances/committed-use-discounts-overview
- https://cloud.google.com/products/compute/pricing