Inactive RDS Read Replica

Service Category

Cloud Provider

AWS

Service Name

AWS RDS

Inefficiency Type

Unused Resource

Explanation

Read replicas are intended to improve performance for read-heavy workloads or support cross-region redundancy. However, it's common for replicas to remain in place even after their intended purpose has passed. In some cases, they were provisioned for scaling or analytics workloads that no longer exist; in others, they are tied to live environments but not actively receiving queries. Since each replica incurs full RDS costs, retaining one that is no longer used leads to unnecessary ongoing expenses.

Relevant Billing Model

Amazon RDS pricing is based on several components:

Compute – Billed hourly based on the instance type and size of each database instance, including read replicas
Storage – Charged per GB provisioned, regardless of usage
I/O Operations – Additional charges for reads and writes, depending on storage type
Data Transfer – Especially relevant for cross-region replication

Read replicas are billed as independent RDS instances, meaning they incur the same base costs as a standard instance—whether or not they are actively serving traffic.

Detection

Identify all existing RDS read replicas and their associated primary instances
Assess whether read traffic is being actively routed to each replica
Review recent query activity to determine if the replica is used for reporting, analytics, or scaling
Evaluate whether the replica is still needed for its original purpose (e.g., disaster recovery, cross-region availability, performance optimization)
Confirm there are no active failover configurations or application connections relying on the replica
Validate with relevant teams (e.g., DBA, application owners) that decommissioning the replica will not impact availability, performance, or redundancy

Remediation

If a read replica is no longer receiving queries and has no clear operational or redundancy purpose, it should be deleted to avoid unnecessary compute and storage costs. Coordinate with database and application teams before removal to ensure that dependencies or failover plans are not disrupted.

Relevant Documentation

RDS Pricing

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