Low EC2 Reserved Instance Coverage
CostLens flags accounts where a significant portion of EC2 compute is running On-Demand, and recommends Reserved Instance purchases to reduce costs by up to 40%.
EC2 Reserved Instances (RIs) provide up to 40% discount over On-Demand pricing in exchange for a 1-year or 3-year commitment. CostLens monitors your RI coverage and flags accounts where more than 30% of your EC2 compute is running On-Demand — a signal that purchasing additional Reserved Instances could significantly reduce your bill.
How it works
CostLens measures your RI coverage
Queries AWS Cost Explorer for your EC2 Reserved Instance coverage over the previous full calendar month. Coverage is the percentage of instance hours that were covered by Reserved Instances vs. charged at On-Demand rates.
Applies the coverage threshold
Accounts with RI coverage below 70% and On-Demand EC2 spend exceeding $200/month are flagged.
Estimates potential savings
Calculates the potential monthly saving by applying a 40% discount to the On-Demand spend that is not currently covered by RIs.
What to do
Step 1 — Identify your stable workloads
Reserved Instances make sense for workloads that run continuously or near-continuously. Review your EC2 instances and identify those that:
- Run 24/7 or at least 8+ hours per day, every day
- Have been running for several months with no planned changes
- Are not candidates for auto-scaling to zero
Step 2 — Choose the right RI type
| RI type | Flexibility | Discount |
|---|---|---|
| Standard RI | Fixed instance family, size, region | Up to 40% off On-Demand |
| Convertible RI | Can be exchanged for different instance types | Up to 31% off On-Demand |
| Compute Savings Plans | Automatically applies to any EC2, Lambda, or Fargate | Up to 66% off |
Consider Compute Savings Plans instead
If you are not sure which instance types you will need, a Compute Savings Plan offers similar discounts with more flexibility. See the Low Savings Plan Coverage check.
Step 3 — Purchase RIs in the AWS Console
Reserved Instances are purchased through the EC2 Console → Reserved Instances → Purchase Reserved Instances. AWS also provides a RI Recommendations tool in Cost Explorer that shows exactly which instance types to purchase based on your usage.
Step 4 — Dismiss the recommendation once purchased
After purchasing RIs, the next billing sync will re-measure your coverage. Once coverage exceeds 70%, the recommendation will automatically move to resolved.
Severity levels
| Severity | Estimated monthly savings |
|---|---|
| critical | >$500 |
| high | $100–$500 |
| medium | $20–$100 |
| low | <$20 |
Required IAM permissions
Included in the CostLens IAM policies from AWS Accounts:
ce:GetReservationCoverage
This is an account-level recommendation
RI coverage is measured across the entire AWS account, not per individual resource. The recommendation appears once per account rather than once per instance.