- A
The application source bundle is missing a required file.
Why wrong: Missing files cause application errors, not necessarily 502.
- B
The security group of the environment does not allow inbound HTTP traffic.
Why wrong: That would cause a timeout or connection refused, not 502.
- C
The environment's environment variables are misconfigured.
Why wrong: Misconfigured env vars cause application errors but not necessarily 502.
- D
The application is not binding to the correct port or is crashing under load.
If the application does not respond, the load balancer returns 502.
Question 444 of 1,750
Elastic Beanstalk 502 Bad Gateway — Application Port Binding
This DOP-C02 practice question tests your understanding of sdlc automation. 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.
A company uses AWS Elastic Beanstalk to deploy a web application. The deployment fails with a '502 Bad Gateway' error. The developer checks the logs and sees that the application is running but returns errors. The environment uses a load balancer. 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 not binding to the correct port or is crashing under load.
A 502 Bad Gateway error from an Elastic Beanstalk environment with a load balancer typically indicates that the reverse proxy (nginx or Apache) is unable to communicate with the application process. Since the logs show the application is running but returning errors, the most likely cause is that the application is not binding to the correct port (expected port 8080 by default) or is crashing under load, causing the proxy to receive no valid response and return a 502.
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 source bundle is missing a required file.
Why it's wrong here
Missing files cause application errors, not necessarily 502.
- ✗
The security group of the environment does not allow inbound HTTP traffic.
Why it's wrong here
That would cause a timeout or connection refused, not 502.
- ✗
The environment's environment variables are misconfigured.
Why it's wrong here
Misconfigured env vars cause application errors but not necessarily 502.
- ✓
The application is not binding to the correct port or is crashing under load.
Why this is correct
If the application does not respond, the load balancer returns 502.
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.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often confuse a 502 Bad Gateway with a security group or missing file issue, but the 502 specifically points to a communication failure between the proxy and the application process, not to external network access or deployment artifacts.
Detailed technical explanation
How to think about this question
In Elastic Beanstalk, the reverse proxy (nginx on Amazon Linux 2) is configured to forward requests to the application on port 8080 (or the PORT environment variable). If the application binds to a different port (e.g., 3000) or crashes under load (e.g., due to memory exhaustion or unhandled exceptions), the proxy receives a connection refused or empty response, which it translates into a 502 Bad Gateway. The health check path (default /) also fails in this scenario, causing the environment to show 'Severe' health status.
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 DOP-C02 question test?
SDLC Automation — This question tests SDLC Automation — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The application is not binding to the correct port or is crashing under load. — A 502 Bad Gateway error from an Elastic Beanstalk environment with a load balancer typically indicates that the reverse proxy (nginx or Apache) is unable to communicate with the application process. Since the logs show the application is running but returning errors, the most likely cause is that the application is not binding to the correct port (expected port 8080 by default) or is crashing under load, causing the proxy to receive no valid response and return a 502.
What should I do if I get this DOP-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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Last reviewed: Jul 4, 2026
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