AWS RDS: Read Replicas vs. Multi-AZ Deployments

Understanding the difference between RDS Read Replicas and Multi-AZ Deployments is critical for the AWS Certified exams. Both features enhance database performance and reliability, but they serve different purposes.

1. Read Replicas (Scaling Reads)

Purpose:

Read Replicas help scale read-heavy workloads by creating asynchronous copies of a primary RDS instance.

Key Characteristics:

✅ Scales Read Traffic – Offloads read requests from the main database.

✅ Asynchronous Replication – Data is replicated eventually (not in real-time).

✅ Up to 15 Read Replicas – Supports multiple replicas for better scalability.

✅ Cross-AZ & Cross-Region Support – Replicas can be in the same AZ, different AZs, or even different regions.

✅ Promotion to Standalone DB – A replica can be promoted to its own independent database if needed.

Use Case Example: Analytics & Reporting

A production database is handling application traffic.
A reporting team wants to run analytics on the same data.
Instead of querying the primary database (which could impact performance), the reporting workload is directed to a Read Replica.

Important Limitations:

🚫 Only for Reads – Supports SELECT queries only (no INSERT, UPDATE, DELETE).