The answer is three possible causes: the target group has no healthy instances, the target’s security group blocks traffic from the ALB, and the target’s response times out. These all prevent the ALB from successfully forwarding requests to a healthy backend, resulting in a 502 Bad Gateway error because the load balancer cannot complete the TCP connection or receive a valid HTTP response within the idle timeout. On the AWS Certified SysOps Administrator Associate SOA-C02 exam, this question tests your understanding of ALB health checks, security group rules, and timeout configurations—common pitfalls include confusing 502 with 404 errors (which stem from incorrect paths) or assuming HTTP methods cause gateway errors. A strong memory tip is to think of the “three T’s” for 502: Targets unhealthy, Traffic blocked, Timeout exceeded.
SOA-C02 Networking and Content Delivery 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. 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 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 the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The target instance is taking too long to respond (e.g., more than the idle timeout).
Option A is correct because if the target group has no healthy instances, the ALB may return 502. Option B is correct because if the target's security group blocks traffic from the ALB, it can cause 502. Option C is correct because if the target's response times out, the ALB returns 502. Option D is wrong because an incorrect path would cause 404, not 502. Option E is wrong because HTTP methods are not the cause of 502 errors.
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 target instance is taking too long to respond (e.g., more than the idle timeout).
Why this is correct
Correct because a slow response can cause the ALB to timeout and return 502.
Related concept
Static NAT maps one inside address to one outside address.
✗
The target instance is configured to respond to a different URL path.
Why it's wrong here
Incorrect because a path mismatch results in 404, not 502.
✗
The ALB is configured with a different HTTP method than the target expects.
Why it's wrong here
Incorrect because HTTP methods are not related to 502 errors.
✓
The security group for the target instances does not allow traffic from the ALB.
Why this is correct
Correct because if the ALB cannot connect to the target, it returns 502.
Related concept
Static NAT maps one inside address to one outside address.
✓
The target group has no healthy instances.
Why this is correct
Correct because no healthy targets can cause 502.
Related concept
Static NAT maps one inside address to one outside address.
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.
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 SOA-C02 NAT questions on configuration and troubleshooting.
Networking and Content Delivery — This question tests Networking and Content Delivery — Static NAT maps one inside address to one outside address..
What is the correct answer to this question?
The correct answer is: The target instance is taking too long to respond (e.g., more than the idle timeout). — Option A is correct because if the target group has no healthy instances, the ALB may return 502. Option B is correct because if the target's security group blocks traffic from the ALB, it can cause 502. Option C is correct because if the target's response times out, the ALB returns 502. Option D is wrong because an incorrect path would cause 404, not 502. Option E is wrong because HTTP methods are not the cause of 502 errors.
What should I do if I get this SOA-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 SOA-C02 NAT questions on configuration and troubleshooting.
What is the key concept behind this question?
Static NAT maps one inside address to one outside address.
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Question Discussion
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