SAP-C02 Design for New Solutions Practice Question
A company runs a critical e-commerce platform on AWS. The application is deployed across multiple Availability Zones in a single region (us-east-1). The architecture includes an Application Load Balancer (ALB), an EC2 Auto Scaling group, and an Amazon RDS for MySQL Multi-AZ database. The application experiences periodic spikes in traffic, and the Auto Scaling group scales out successfully. However, during a recent traffic spike, the database CPU utilization reached 90%, causing increased latency and some database connection timeouts. The company needs to improve the database performance to handle the spikes without over-provisioning. The solutions architect must design a solution that reduces the load on the primary database instance and improves read scalability. The application is read-heavy, with a read-to-write ratio of 80:20. Which solution should the architect implement?
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 one or more Amazon RDS Read Replicas in the same region and configure the application to route read queries to the read replica endpoint.
Amazon RDS Read Replicas can offload read traffic from the primary instance, reducing CPU utilization. For a read-heavy workload (80:20), creating Read Replicas in the same region and routing read queries to them is the most effective solution to improve read scalability without over-provisioning the primary. Option D is correct. Option A (ElastiCache) is more suited for caching but does not offload database reads directly; it requires significant application changes and may not handle all query patterns. Option B (scaling up instance class) has scaling limits and is less cost-effective; Multi-AZ is for high availability, not read scaling. Option C (DynamoDB) is a different database; migrating would be complex and unnecessary.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Implement an Amazon ElastiCache Redis cluster to cache frequent database queries.
Why it's wrong here
ElastiCache caches repeated query results but does not serve the 80% read volume directly from replicas, so the primary still absorbs most reads. It is tempting because caching genuinely reduces database load for repetitive queries; it would be correct alongside, not instead of, read replicas.
- ✗
Increase the DB instance class to a larger size and enable Multi-AZ with synchronous replication.
Why it's wrong here
Vertical scaling of the primary instance leaves the 80:20 read-heavy load concentrated on one node, so CPU saturation recurs at the next spike. Larger instances suit sustained, predictable workloads needing more memory or IOPS, not read distribution. Read replicas offload the primary's read traffic.
- ✗
Migrate the database to Amazon DynamoDB and use DynamoDB Accelerator (DAX) for read performance.
Why it's wrong here
DynamoDB is a NoSQL store, so migrating the existing MySQL schema and relational queries requires application rewrite, and DAX accelerates key-value reads rather than offloading an RDS primary. It is tempting because DynamoDB genuinely suits greenfield, non-relational workloads needing massive scale.
- ✓
Create one or more Amazon RDS Read Replicas in the same region and configure the application to route read queries to the read replica endpoint.
Why this is correct
Read Replicas offload read traffic from the primary via asynchronous MySQL replication, directly addressing the 80:20 read-heavy ratio and the 90% primary CPU saturation. The application routes SELECT queries to the replica endpoint, restoring primary capacity for writes without over-provisioning.
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