RDS vs Aurora cost comparison

RDS vs Aurora — same database, different bill

Aurora-MySQL and Aurora-Postgres are AWS's "managed-managed" databases — wire-compatible with RDS engines but with completely different storage architecture. The pricing implications are substantial when you have read replicas.

Architecture difference (the cost driver)

• RDS: each replica has its OWN copy of storage. 500 GB primary + 2 replicas = 1,500 GB billed.
• Aurora: shared cluster storage. 500 GB primary + 2 replicas = 500 GB billed.

For read-heavy workloads with multiple replicas, this is huge. Default scenario:

• RDS storage: 500 × 0.115 × 3 = $172/mo
• Aurora storage: 500 × 0.10 = $50/mo
• $122/mo savings on storage alone

Where Aurora costs more

• Compute: 20-30% premium per instance vs RDS
• I/O: per-request billing on Aurora Standard ($0.20 per million)
• Backtrack / backup retention: per-second time-travel costs on top

When Aurora wins

• 2+ read replicas
• High availability is non-negotiable (Aurora Multi-AZ is faster failover)
• Need read scaling (Aurora can have up to 15 replicas with shared storage)
• Like the auto-storage-grow feature

When RDS wins

• Single instance / no replicas — Aurora premium pure cost
• Predictable workload, doesn't need Aurora features
• I/O-heavy with consistent traffic (Aurora Standard's per-IOPS billing surprises)
• Cost-constrained startups (RDS gp3 instances are dirt cheap)