RDS MySQL Read Replicas: Offload Read Traffic
A company has a high-traffic e-commerce application that uses Amazon RDS for MySQL. During flash sales, the database experiences high read load causing slow page loads. The application is read-heavy with occasional writes. Which design change would provide the most immediate performance improvement?
Quick Answer
The answer is to create read replicas of the RDS instance, as this directly offloads read traffic from the primary database to handle read scaling for high-traffic workloads. By promoting one or more read replicas, the application can route SELECT queries to these copies, reducing the load on the source instance and improving page load times during flash sales without affecting write capacity. On the AWS Certified Database Specialty DBS-C01 exam, this scenario tests your understanding of the fundamental difference between read scaling and high availability—a common trap is confusing Multi-AZ (which only provides failover, not read offloading) with read replicas. Remember that ElastiCache is for caching specific query results, not for scaling general read load, and upgrading the instance is a vertical scaling approach that is less elastic and cost-effective than adding replicas. Memory tip: “Replicas for reads, Multi-AZ for needs”—if the question says “read-heavy” or “read scaling,” always think replicas first.
⚠ Common exam trap
Test-takers frequently confuse Multi-AZ with read scaling, but Multi-AZ does not allow the standby to serve read traffic, making it ineffective for reducing read load.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Create read replicas of the RDS instance
Creating read replicas of the RDS instance offloads SELECT queries from the primary database, directly addressing the high read load during flash sales. Read replicas are asynchronous copies that can serve read traffic, reducing the burden on the primary instance and improving page load times for read-heavy workloads.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Add an Amazon ElastiCache layer
Why it's wrong here
Caching requires application changes and may miss dynamic data.
- ✓
Create read replicas of the RDS instance
Why this is correct
Read replicas offload read traffic, improving performance.
- ✗
Enable Multi-AZ deployment
Why it's wrong here
Multi-AZ provides failover, not read scaling.
- ✗
Upgrade to a larger instance type
Why it's wrong here
Vertical scaling is less elastic and more costly.
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Same concept, more angles
1 more way this is tested on DBS-C01
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. A company uses Amazon RDS for PostgreSQL for its e-commerce platform. The application team reports increasing read latency on the primary instance during sales events. Which action should be taken to reduce read load on the primary?
medium- A.Enable Multi-AZ deployment
- B.Migrate to Amazon DynamoDB
- ✓ C.Create one or more read replicas
- D.Increase the instance size of the primary
Why C: Creating one or more read replicas offloads read traffic from the primary RDS for PostgreSQL instance, directly addressing the increased read latency during sales events. Read replicas are asynchronous replicas that can serve SELECT queries, reducing the load on the primary without requiring application changes to the write path. This is the standard AWS solution for scaling read-heavy workloads in RDS.
JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This DBS-C01 practice question is part of Courseiva's free Amazon Web Services certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the DBS-C01 exam.