- A
The target instance is taking too long to respond (e.g., more than the idle timeout).
Why wrong: Incorrect. If the target takes longer than the idle timeout to respond, the ALB returns a 504 Gateway Timeout, not a 502 Bad Gateway. A 502 results from an invalid or incomplete response, not timeout.
- B
The target instance is configured to respond to a different URL path.
Why wrong: Incorrect. If the target is configured to respond to a different URL path, it may return a 404 Not Found or other error, but that is a valid HTTP response and does not cause a 502 error.
- C
The ALB is configured with a different HTTP method than the target expects.
Correct. If the ALB sends an HTTP method (e.g., PATCH) that the target does not support, the target may close the connection or send an invalid response, causing the ALB to see a malformed response and return a 502.
- D
The security group for the target instances does not allow traffic from the ALB.
Correct. If the security group for the target instances does not allow traffic from the ALB, the ALB cannot establish a connection to the target, resulting in a 502 error.
- E
The target group has no healthy instances.
Correct. If the target group has no healthy instances, the ALB cannot forward the request to any target, and it returns a 502 Bad Gateway.
SOA-C02 502 Bad Gateway Practice Question
This SOA-C02 practice question tests your understanding of networking and content delivery. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. A key principle to apply: 502 Bad Gateway. 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 SysOps Administrator is troubleshooting an issue where an Application Load Balancer (ALB) returns 502 Bad Gateway errors. Which THREE are possible causes? (Choose THREE.)
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 configured with a different HTTP method than the target expects.
ALB returns 502 Bad Gateway when it receives an invalid, malformed, or incomplete response from the target, or when it cannot establish a connection to a healthy target. Option C is correct because if the ALB sends an HTTP method that the target does not support, the target may close the connection or send an invalid response, leading to a 502 error. Option D is correct because if the target security group does not allow traffic from the ALB, the connection fails, resulting in 502. Option E is correct because if no healthy targets exist in the target group, the ALB cannot forward requests, returning 502. Option A is incorrect: a target taking longer than the idle timeout causes a 504 Gateway Timeout, not a 502. Option B is incorrect: a different URL path typically results in a 404 or similar error, not a 502.
Key principle: 502 Bad Gateway
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 target instance is taking too long to respond (e.g., more than the idle timeout).
Why it's wrong here
Incorrect. If the target takes longer than the idle timeout to respond, the ALB returns a 504 Gateway Timeout, not a 502 Bad Gateway. A 502 results from an invalid or incomplete response, not timeout.
- ✗
The target instance is configured to respond to a different URL path.
Why it's wrong here
Incorrect. If the target is configured to respond to a different URL path, it may return a 404 Not Found or other error, but that is a valid HTTP response and does not cause a 502 error.
- ✓
The ALB is configured with a different HTTP method than the target expects.
- ✓
The security group for the target instances does not allow traffic from the ALB.
Why this is correct
Correct. If the security group for the target instances does not allow traffic from the ALB, the ALB cannot establish a connection to the target, resulting in a 502 error.
Related concept
502 Bad Gateway
- ✓
The target group has no healthy instances.
Common exam traps
Common exam trap: answer the scenario, not the keyword
A common mistake is to assume that any timeout results in a 502 error. However, a target response timeout (exceeding the idle timeout) leads to a 504 Gateway Timeout, while a 502 indicates an invalid response or connection issue, such as a method mismatch or blocked traffic.
Detailed technical explanation
How to think about this question
The ALB's idle timeout is distinct from the request timeout; the idle timeout governs how long the ALB keeps an idle connection open, while the request timeout (default 60 seconds) is the maximum time the ALB waits for a response from the target after forwarding the request. If the target sends a response header but the body is delayed beyond the idle timeout, the ALB may still return a 502. Additionally, security group misconfigurations (Option D) cause the ALB to receive no response at all, leading to a 502, and an unhealthy target group (Option E) means the ALB has no valid targets to forward traffic to, also resulting in a 502.
KKey Concepts to Remember
- 502 Bad Gateway
- Target Group Health Checks
- Security Group Rules
- HTTP Method Mismatch
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
502 Bad Gateway
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 502 Bad Gateway, then practise related SOA-C02 questions on the same topic to reinforce the concept.
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FAQ
Questions learners often ask
What does this SOA-C02 question test?
Networking and Content Delivery — This question tests Networking and Content Delivery — 502 Bad Gateway.
What is the correct answer to this question?
The correct answer is: The ALB is configured with a different HTTP method than the target expects. — ALB returns 502 Bad Gateway when it receives an invalid, malformed, or incomplete response from the target, or when it cannot establish a connection to a healthy target. Option C is correct because if the ALB sends an HTTP method that the target does not support, the target may close the connection or send an invalid response, leading to a 502 error. Option D is correct because if the target security group does not allow traffic from the ALB, the connection fails, resulting in 502. Option E is correct because if no healthy targets exist in the target group, the ALB cannot forward requests, returning 502. Option A is incorrect: a target taking longer than the idle timeout causes a 504 Gateway Timeout, not a 502. Option B is incorrect: a different URL path typically results in a 404 or similar error, not a 502.
What should I do if I get this SOA-C02 question wrong?
Review 502 Bad Gateway, then practise related SOA-C02 questions on the same topic to reinforce the concept.
What is the key concept behind this question?
502 Bad Gateway
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Last reviewed: Jul 4, 2026
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