← SOA-C02·Amazon Web Services

Question 774 of 1,546

Monitoring, Logging, and Remediation →hardMultiple ChoiceObjective-mapped

Diagnosing High ALB Latency Due to Connection Queuing

This SOA-C02 practice question tests your understanding of monitoring, logging, and remediation. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.

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?

Clue words in this question

Noticing these words before you look at the options changes how you read each choice.

Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.

A
The ALB is experiencing connection queuing due to a high number of concurrent requests.
High concurrency can cause the ALB to queue requests, increasing response time without backend load.
B
The application is CPU-bound on the EC2 instances.
Why wrong: CPUUtilization is low, so the application is not CPU-bound.
C
The EC2 instances are throttled due to a burst balance limit.
Why wrong: Throttling would cause high CPU or I/O wait, not low CPU.
D
The application is waiting on a database query that is slow.
Why wrong: Database wait would not cause low CPU; the application would be waiting, but CPU might still be used for other tasks.

Full breakdown with real-world context →

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

✓

The ALB is experiencing connection queuing due to a high number of concurrent requests.

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.

Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.

Answer analysis

Option-by-option breakdown

For each option: why learners choose it and why it is or isn't the right answer here.

✓
The ALB is experiencing connection queuing due to a high number of concurrent requests.
Why this is correct
High concurrency can cause the ALB to queue requests, increasing response time without backend load.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
The application is CPU-bound on the EC2 instances.
Why it's wrong here
CPUUtilization is low, so the application is not CPU-bound.
✗
The EC2 instances are throttled due to a burst balance limit.
Why it's wrong here
Throttling would cause high CPU or I/O wait, not low CPU.
✗
The application is waiting on a database query that is slow.
Why it's wrong here
Database wait would not cause low CPU; the application would be waiting, but CPU might still be used for other tasks.

Common exam traps

Common exam trap: answer the scenario, not the keyword

The trap here is that candidates assume high latency always means the backend is overloaded, but the question deliberately shows low CPU/memory to force you to consider load balancer-level queuing as the root cause.

Detailed technical explanation

How to think about this question

The ALB's connection queue is managed by the target group's 'slow start' and 'deregistration delay' settings, but the key limit is the number of concurrent connections the ALB can maintain to each target (default 1024). When this limit is reached, the ALB buffers requests in a queue, and the TargetResponseTime metric reflects the total time from request receipt to response start, including queuing delay. In contrast, the backend's CPU and memory remain low because the requests are not being dispatched to the instances.

KKey Concepts to Remember

Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.

TExam Day Tips

Watch for words such as best, first, most likely and least administrative effort.
Review why wrong options are wrong, not only why the correct option is correct.

Key takeaway

Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.

Real-world example

How this comes up in practice

An e-commerce site experiences heavy traffic on Black Friday and near-zero traffic during off-peak weeks. Rather than provisioning permanent large VMs, the team uses auto-scaling groups that add capacity automatically under load and reduce it overnight. Questions like this test whether you understand elasticity, availability zones, and cloud compute scaling patterns.

What to study next

Got this wrong? Here's your next step.

Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.

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FAQ

Questions learners often ask

What does this SOA-C02 question test?

Monitoring, Logging, and Remediation — This question tests Monitoring, Logging, and Remediation — Read the scenario before looking for a memorised answer..

What is the correct answer to this question?

The correct answer is: The ALB is experiencing connection queuing due to a high number of concurrent requests. — 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.

What should I do if I get this SOA-C02 question wrong?

Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.

Are there clue words in this question I should notice?

Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.

What is the key concept behind this question?

Read the scenario before looking for a memorised answer.

About these practice questions

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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. 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?

medium

✓ A.ALB TargetResponseTime and EC2 CPUUtilization
B.EC2 CPUUtilization and NetworkIn
C.EC2 StatusCheckFailed and ALB UnhealthyHostCount
D.ALB RequestCount and HealthyHostCount

Why A: The correct answer is A because 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.

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: Option A is correct because 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.

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