Aurora vs RDS

Aurora and RDS are both AWS-managed database services, but Aurora re-engineers the storage layer for better performance and availability. Understanding when the premium is worth it is key for cloud architecture design.

Architecture Differences

RDS runs standard database engines (MySQL, PostgreSQL, MariaDB, Oracle, SQL Server) on EC2 instances with EBS volumes. Replication is handled by the database engine's native mechanism: streaming replication for PostgreSQL, binary log replication for MySQL.

Aurora replaces the storage layer with a distributed, fault-tolerant storage system spanning six copies across three AZs. The compute layer runs modified MySQL or PostgreSQL. Only WAL records are written to storage, reducing write amplification and I/O.

Performance Characteristics

Aurora's distributed storage delivers up to 5x MySQL throughput and 3x PostgreSQL throughput compared to the same engines on RDS. The improvement comes from reduced write amplification, parallel I/O, and the shared storage architecture that eliminates replica lag.

For read-heavy workloads, Aurora's 15 read replicas (versus RDS's 5) sharing the same storage volume provide more read capacity with near-zero replication lag.

Trade-offs

Aurora costs 20-50% more than equivalent RDS instances. For many workloads, standard RDS provides sufficient performance at lower cost. The decision should be based on actual performance requirements, not aspirational ones.

RDS supports five database engines while Aurora supports only MySQL and PostgreSQL. For Oracle or SQL Server workloads, RDS is the only managed AWS option.

When to Upgrade from RDS to Aurora

Consider Aurora when: your RDS instance is hitting I/O limits, you need more than 5 read replicas, you want faster failover (typically under 30 seconds versus 60+ for RDS), or you need multi-region replication with Aurora Global Database.

Stay with RDS when: your workload is modest, cost is the primary concern, you need Oracle/SQL Server, or performance on RDS is adequate.

Real-World Usage

Aurora powers Samsung, Dow Jones, and Capital One. RDS hosts workloads at thousands of companies that need managed databases without Aurora's premium pricing.

Explore cloud database patterns and high availability design. See our system design guide and pricing.