Underutilized RDS Commitment Due to Workload Drift

Jason DiDomenico

Service Category

Databases

Cloud Provider

AWS

Service Name

AWS RDS

Inefficiency Type

Overcommitted Reservation

Explanation

RDS workloads often evolve — changing engine types, rightsizing instances, or shifting to Aurora or serverless models. When these changes occur after Reserved Instances have been purchased, the existing commitments may no longer match active usage. This results in silent overspend, as underutilized RIs continue billing without offsetting usage.

Unlike Convertible EC2 RIs, RDS RIs cannot be exchanged. Selling unused RDS RIs is not supported. In rare cases, AWS Support may approve a goodwill adjustment, but this is not guaranteed. The most effective way to recover value is to steer eligible workloads back toward the reserved configuration.

Relevant Billing Model

Standard RDS Reserved Instances are billed hourly regardless of instance usage
RIs are tied to specific configurations and cannot be modified once purchased
If RDS usage patterns change or migrate away from covered configurations, the RI continues to accrue cost without providing benefit

Detection

Identify underutilized RDS Reserved Instances using billing and utilization data
Break down the instance classes, engines, and regions with low or zero usage
Trace whether existing workloads have moved off those configurations — and why
Quantify the cost of unused commitment to prioritize remediation

Remediation

Evaluate whether current or new workloads can run on the reserved instance types
Prioritize launching new RDS instances that align with the unused commitment
Where feasible, upgrade or shift workloads to covered instance classes while monitoring performance and future fit
Document changes made to consume the commitment and reassess once the reservation expires
In rare cases, contact AWS Support to request a reservation adjustment — note that approval depends on RI type, remaining term, and value parity

Relevant Documentation

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