Troubleshooting ALB Latency Spikes
A company is running a web application on EC2 instances behind an Application Load Balancer. The application experiences intermittent latency spikes. The SysOps administrator needs to identify the root cause. Which set of CloudWatch metrics should be analyzed first?
Quick Answer
The correct answer is to analyze ALB TargetResponseTime and EC2 CPUUtilization first. This pairing is essential because TargetResponseTime directly measures how long the backend takes to respond to the load balancer, while CPUUtilization reveals whether the EC2 instance is under compute strain. When you see a latency spike in TargetResponseTime coinciding with high CPUUtilization, it strongly indicates a compute bottleneck—the instance is overwhelmed and cannot process requests quickly enough. On the AWS Certified SysOps Administrator Associate SOA-C02 exam, this question tests your ability to correlate application-layer metrics with infrastructure metrics, a core troubleshooting skill. A common trap is to start with ALB RequestCount or network metrics, but those won’t pinpoint whether the delay is on the target side. Remember the memory tip: “Time plus CPU tells the true story”—if the target takes long and the CPU is high, the instance is the culprit.
⚠ Common exam trap
Candidates often confuse latency metrics with availability metrics, choosing options like C or D that indicate failures or traffic volume, rather than the performance-specific metrics needed to diagnose intermittent slowness.
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
✓
ALB TargetResponseTime and EC2 CPUUtilization
Intermittent latency spikes in a web application behind an Application Load Balancer (ALB) are most directly investigated by correlating ALB TargetResponseTime (which measures the time taken for the target to respond to the ALB) with EC2 CPUUtilization (which indicates whether the instance is under compute pressure). A spike in TargetResponseTime alongside high CPUUtilization suggests the EC2 instance is struggling to process requests, pointing to a compute bottleneck as 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.
- ✓
ALB TargetResponseTime and EC2 CPUUtilization
Why this is correct
TargetResponseTime directly measures latency; CPUUtilization may indicate resource contention.
- ✗
EC2 CPUUtilization and NetworkIn
Why it's wrong here
Useful but not directly correlated to latency spikes.
- ✗
EC2 StatusCheckFailed and ALB UnhealthyHostCount
Why it's wrong here
These indicate instance failures, not intermittent latency.
- ✗
ALB RequestCount and HealthyHostCount
Why it's wrong here
These show request volume and health, not latency.
Go deeper
Related to this question
About these practice questions
This SOA-C02 question is part of Courseiva's 247-question bank — original exam-style content with full explanations and wrong-answer analysis, never real exam questions or exam dumps. Learn why practice questions differ from exam dumps →
Same concept, more angles
2 more ways this is tested on SOA-C02
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. An application running on EC2 instances behind an Application Load Balancer (ALB) is experiencing increased latency. The SysOps administrator checks CloudWatch and sees that the ALB's TargetResponseTime is high, but the backend EC2 instance's CPUUtilization and MemoryUtilization are low. What is the most likely cause?
hard- ✓ A.The ALB is experiencing connection queuing due to a high number of concurrent requests.
- B.The application is CPU-bound on the EC2 instances.
- C.The EC2 instances are throttled due to a burst balance limit.
- D.The application is waiting on a database query that is slow.
Why A: When TargetResponseTime is high but backend CPU and memory are low, the bottleneck is not the compute capacity of the instances but rather the ALB's ability to forward requests. The ALB has a default connection queue limit (typically 1024 pending connections per target group), and when concurrent requests exceed that, new requests are queued, increasing response time without stressing the backend. This is a classic sign of connection queuing at the load balancer level.
Variation 2. A company runs a critical web application on EC2 instances behind an Application Load Balancer (ALB) in an Auto Scaling group. The application experiences intermittent latency spikes. The SysOps administrator has enabled detailed CloudWatch metrics on the ALB and the EC2 instances. The administrator notices that during the latency spikes, the ALB's TargetResponseTime metric increases, but the EC2 instance's CPU utilization and memory usage remain normal. The administrator also observes that the number of concurrent connections to the ALB spikes during these periods. Which action should the administrator take to identify the root cause?
hard- ✓ A.Analyze the ALB's ActiveConnectionCount and RequestCountPerTarget metrics to see if the load balancer is reaching its connection limit.
- B.Check the RDS database's DatabaseConnections metric to see if the database is overwhelmed.
- C.Enable VPC Flow Logs and analyze the traffic patterns for dropped packets.
- D.Enable detailed monitoring on the EC2 instances to capture CPU credits for burstable instances.
Why A: The ALB's ActiveConnectionCount and RequestCountPerTarget metrics directly indicate whether the load balancer is approaching its connection limit (default 50,000 for ALBs). During latency spikes, if concurrent connections spike but instance CPU/memory are normal, the bottleneck is likely at the load balancer level, not the instances. Analyzing these metrics helps determine if the ALB is queuing or dropping requests due to connection limits, causing increased TargetResponseTime.
JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This SOA-C02 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 SOA-C02 exam.