PAS-C01 Technology Practice Question
A company runs a critical web application on Amazon EC2 instances behind an Application Load Balancer (ALB). The application uses an Amazon RDS for PostgreSQL database. The operations team reports that the application becomes unresponsive for about 30 seconds every hour at the same time. The team checks the ALB access logs and notices that during the outage, the ALB returns HTTP 504 errors. The RDS monitoring shows a spike in CPU usage and active connections during the same period. The application team confirms there are no scheduled jobs during that time. What should the team do to diagnose the root cause?
⚠ Common exam trap
Test-takers frequently confuse HTTP 504 errors with ALB or EC2 health check failures, but 504 specifically indicates the ALB received no response from the target (often due to database timeout), not that the target is unhealthy.
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
✓
Check the RDS Enhanced Monitoring metrics for the database instance to identify resource bottlenecks such as high memory pressure or disk I/O.
The symptoms—hourly 30-second unresponsiveness, HTTP 504 errors from the ALB, and a correlated spike in RDS CPU and active connections—point to a database-side bottleneck. RDS Enhanced Monitoring provides OS-level metrics (memory, disk I/O, CPU) that can reveal resource contention or throttling events (e.g., swap usage, IOPS exhaustion) not visible in standard CloudWatch metrics, enabling precise root cause identification.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Review the security group rules for the database to ensure the application can connect.
Why it's wrong here
Security group rules are static and unlikely to cause periodic outages.
- ✗
Review the ALB target group health checks and ensure the EC2 instances are passing the health check.
Why it's wrong here
Health checks would fail if instances are unhealthy, but the issue is likely database-related, not instance-level.
- ✗
Increase the EC2 instance size to handle more concurrent connections.
Why it's wrong here
The symptoms indicate a database bottleneck; scaling EC2 instances does not resolve database issues.
- ✓
Check the RDS Enhanced Monitoring metrics for the database instance to identify resource bottlenecks such as high memory pressure or disk I/O.
Why this is correct
Enhanced Monitoring provides detailed OS-level metrics to pinpoint the root cause of the database spike.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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