- A
The application is not deployed to the EC2 instances.
Why wrong: If not deployed, the health check would fail, but the error message points to the target path and port.
- B
The application is listening on a different port than the health check expects.
The health check URL shows port 80, but the application may be configured to listen on a custom port, causing the health check to fail.
- C
The security group for the EC2 instances is blocking traffic on port 80.
Why wrong: The health check is made by the load balancer, and if the security group blocks it, the health check would fail, but the error message shows the health check target is not responding, indicating the application is not listening.
- D
The load balancer is not configured to listen on port 80.
Why wrong: The load balancer listener is separate from the health check target; the health check is failing because the application is not responding on that path.
Quick Answer
The answer is a port mismatch between the application and the Elastic Beanstalk health check target. This is the most likely cause because the default health check path is configured to hit HTTP port 80, but your Node.js application may be listening on a custom port, such as 8080 or 3000, causing the ELB health check to fail with the "not responding" error. On the AWS Certified Developer Associate DVA-C02 exam, this scenario tests your understanding of how Elastic Beanstalk integrates with the load balancer and the importance of aligning the health check port with the application’s actual listening port. A common trap is assuming the issue is a security group or deployment failure, but the specific log message points directly to a target port problem. Remember the memory tip: "Port 80 is the default, but your app may not be a default listener."
DVA-C02 Troubleshooting and Optimization Practice Question
This DVA-C02 practice question tests your understanding of troubleshooting and optimization. Match the stated requirement to the specific cloud service, access model, or configuration option — many options are valid in isolation but not for this scenario. 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.
A company is using AWS Elastic Beanstalk for a Node.js application. The environment's health is 'Severe' and the logs show 'ELB health check target http://:80/ is not responding'. 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.
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 is listening on a different port than the health check expects.
Option D is correct because the health check path is set to HTTP port 80 by default, but the application may be listening on a custom port. Option A is wrong because if the application is not deployed, the error would be different. Option B is wrong because the health check error is about the target, not the load balancer. Option C is wrong because the security group would block all traffic, not just health checks.
Key principle: NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
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 is not deployed to the EC2 instances.
Why it's wrong here
If not deployed, the health check would fail, but the error message points to the target path and port.
- ✓
The application is listening on a different port than the health check expects.
Why this is correct
The health check URL shows port 80, but the application may be configured to listen on a custom port, causing the health check to fail.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Static NAT maps one inside address to one outside address.
- ✗
The security group for the EC2 instances is blocking traffic on port 80.
Why it's wrong here
The health check is made by the load balancer, and if the security group blocks it, the health check would fail, but the error message shows the health check target is not responding, indicating the application is not listening.
- ✗
The load balancer is not configured to listen on port 80.
Why it's wrong here
The load balancer listener is separate from the health check target; the health check is failing because the application is not responding on that path.
Common exam traps
Common exam trap: NAT rules depend on direction and matching traffic
NAT is not only about the public address. The inside/outside interface roles and the ACL or rule that matches traffic are just as important.
Trap categories for this question
Command / output trap
The health check is made by the load balancer, and if the security group blocks it, the health check would fail, but the error message shows the health check target is not responding, indicating the application is not listening.
Detailed technical explanation
How to think about this question
NAT questions usually test address translation, overload/PAT behaviour, static mappings and whether the right traffic is being translated. Read the interface direction and address terms carefully.
KKey Concepts to Remember
- Static NAT maps one inside address to one outside address.
- PAT allows many inside hosts to share one public address using ports.
- Inside local and inside global describe the private and translated addresses.
- NAT ACLs identify traffic for translation, not always security filtering.
TExam Day Tips
- Identify inside and outside interfaces first.
- Check whether the scenario needs static NAT, dynamic NAT or PAT.
- Do not confuse NAT matching ACLs with normal packet-filtering intent.
Key takeaway
NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
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.
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related DVA-C02 NAT questions on configuration and troubleshooting.
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Troubleshooting and Optimization — study guide chapter
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FAQ
Questions learners often ask
What does this DVA-C02 question test?
Troubleshooting and Optimization — This question tests Troubleshooting and Optimization — Static NAT maps one inside address to one outside address..
What is the correct answer to this question?
The correct answer is: The application is listening on a different port than the health check expects. — Option D is correct because the health check path is set to HTTP port 80 by default, but the application may be listening on a custom port. Option A is wrong because if the application is not deployed, the error would be different. Option B is wrong because the health check error is about the target, not the load balancer. Option C is wrong because the security group would block all traffic, not just health checks.
What should I do if I get this DVA-C02 question wrong?
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related DVA-C02 NAT questions on configuration and troubleshooting.
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?
Static NAT maps one inside address to one outside address.
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Last reviewed: Jun 20, 2026
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