SAP-C02 Design for New Solutions Practice Question
A company is running a production web application on AWS using an Application Load Balancer (ALB) in front of an Auto Scaling group of EC2 instances. The application uses a MySQL database hosted on Amazon RDS with Multi-AZ enabled. Recently, during a traffic spike, some users experienced increased latency and occasional 503 errors. The operations team noticed that the database CPU utilization reached 100% and the number of database connections peaked at the maximum limit. The application team confirmed that the application uses connection pooling on the EC2 instances but the pool size is fixed. Which solution should the solutions architect recommend to prevent recurrence?
⚠ Common exam trap
Candidates often confuse connection exhaustion with CPU or memory bottlenecks and choose vertical scaling (Option B) or read replicas (Option A), missing that the core issue is the fixed connection pool size and the database's max connections limit, which RDS Proxy directly addresses by pooling and reusing connections.
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
✓
Implement Amazon RDS Proxy to manage database connections.
The issue stems from database connections hitting the maximum limit, causing CPU saturation and 503 errors. Amazon RDS Proxy sits between the application and the database, efficiently managing and pooling connections from the EC2 instances, reducing the number of open connections to the RDS instance and preventing connection exhaustion. This allows the existing connection pooling on the EC2 side to scale without overwhelming the database, directly addressing the root cause.
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 read replicas to offload read queries.
Why it's wrong here
Read replicas only offload read traffic; the stem shows CPU and connection saturation driven by write load and a fixed pool, so replicas leave both untouched. They are tempting because they genuinely scale read-heavy workloads, and would be correct if the bottleneck were read queries rather than writes and connection count.
- ✗
Increase the DB instance class to a larger size.
Why it's wrong here
A larger instance class raises the connection ceiling only proportionally and leaves the fixed pool exhausting connections at peak; the bottleneck is connection count, not raw CPU alone. Scaling up is the right remedy when a single query or working set genuinely saturates CPU or memory on an adequately pooled workload.
- ✓
Implement Amazon RDS Proxy to manage database connections.
Why this is correct
Amazon RDS Proxy pools and shares database connections, absorbing traffic spikes so the fixed application-side pools no longer exhaust the RDS connection limit. This relieves the 100% CPU and connection ceiling causing latency and 503 errors.
- ✗
Increase the maximum number of EC2 instances in the Auto Scaling group.
Why it's wrong here
Adding EC2 instances increases concurrent application connections to RDS, worsening the connection-limit exhaustion and CPU saturation. It tempts because horizontal scaling relieves application-tier load, and it is correct when the bottleneck is EC2 capacity — but here the constraint is database connections, addressed by RDS Proxy pooling.
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