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DVA-C02 Development with AWS Services Practice Question

This DVA-C02 practice question tests your understanding of development with aws services. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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 Amazon EC2 instances behind an Application Load Balancer (ALB) intermittently returns 503 errors. The ALB health checks are failing for some instances intermittently. The developer checks the instance system logs and finds no application errors. What is the most likely cause of the health check failures?

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.

Question 1easymultiple choice

Full question →

A
The application on the instances is experiencing resource exhaustion (e.g., memory or CPU) which causes it to stop responding to health checks temporarily
Intermittent failures suggest transient issues like high resource utilization. The application may become unresponsive during spikes, causing health checks to fail until resources are freed.
B
The security group for the instances does not allow inbound traffic from the ALB on the health check port
Why wrong: Security group misconfiguration would cause health checks to fail consistently, not intermittently.
C
The health check path is not configured correctly and the default path returns a 404 status
Why wrong: Incorrect health check configuration would result in persistent failures for all instances.
D
The target group is not configured with the correct protocol
Why wrong: Protocol mismatch would cause consistent health check failures.

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 application on the instances is experiencing resource exhaustion (e.g., memory or CPU) which causes it to stop responding to health checks temporarily

Intermittent 503 errors from the ALB combined with intermittent health check failures and no application errors in the system logs strongly point to transient resource exhaustion (CPU or memory) on the EC2 instances. When an instance runs out of memory or CPU, the application process may become unresponsive or be killed by the OS (e.g., OOM killer), causing it to fail health checks temporarily. Once resources are freed (e.g., after a spike subsides), the application resumes responding, which explains the intermittent nature of the failures.

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 application on the instances is experiencing resource exhaustion (e.g., memory or CPU) which causes it to stop responding to health checks temporarily
Why this is correct
Intermittent failures suggest transient issues like high resource utilization. The application may become unresponsive during spikes, causing health checks to fail until resources are freed.
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 security group for the instances does not allow inbound traffic from the ALB on the health check port
Why it's wrong here
Security group misconfiguration would cause health checks to fail consistently, not intermittently.
✗
The health check path is not configured correctly and the default path returns a 404 status
Why it's wrong here
Incorrect health check configuration would result in persistent failures for all instances.
✗
The target group is not configured with the correct protocol
Why it's wrong here
Protocol mismatch would cause consistent health check failures.

Common exam traps

Common exam trap: answer the scenario, not the keyword

The trap here is that candidates often assume health check failures are always due to misconfiguration (security groups, paths, or protocols) and overlook transient resource exhaustion, which is a common cause of intermittent failures in production.

Detailed technical explanation

How to think about this question

Under the hood, ALB health checks are sent from the ALB's private IP addresses to the target instances on the configured health check port and path. If the application process is unresponsive due to resource exhaustion, the TCP connection may time out or the HTTP response may be delayed beyond the health check interval (default 30 seconds) and threshold (default 5 consecutive failures). In real-world scenarios, memory leaks or CPU spikes from burst traffic are common causes of such intermittent failures, and monitoring CloudWatch metrics like CPUUtilization and MemoryUtilization can help correlate the timing.

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

A healthcare organisation deploys an application with a public-facing web tier and a private database tier. The database subnet has no public IP and only accepts connections from the web tier's security group. Questions like this test whether you can design cloud network isolation using VNets/VPCs, subnets, and security group rules.

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 DVA-C02 question test?

Development with AWS Services — This question tests Development with AWS Services — Read the scenario before looking for a memorised answer..

What is the correct answer to this question?

The correct answer is: The application on the instances is experiencing resource exhaustion (e.g., memory or CPU) which causes it to stop responding to health checks temporarily — Intermittent 503 errors from the ALB combined with intermittent health check failures and no application errors in the system logs strongly point to transient resource exhaustion (CPU or memory) on the EC2 instances. When an instance runs out of memory or CPU, the application process may become unresponsive or be killed by the OS (e.g., OOM killer), causing it to fail health checks temporarily. Once resources are freed (e.g., after a spike subsides), the application resumes responding, which explains the intermittent nature of the failures.

What should I do if I get this DVA-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.

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