SOA-C02 Application Load Balancer (ALB) Practice Question
A SysOps administrator is troubleshooting an issue where an Application Load Balancer (ALB) is returning 503 errors to clients. The target group has healthy EC2 instances. Which THREE possible causes should the administrator investigate? (Choose three.)
⚠ Common exam trap
The trap is that candidates often assume a 503 error always indicates unhealthy targets, but the question explicitly states healthy instances, so they must consider other causes like security group misconfiguration, ALB capacity limits, or the load balancer not being attached to a subnet.
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 load balancer is not attached to a subnet.
If the load balancer is not attached to a subnet, it cannot route traffic to targets and may return 503 errors. Option B is correct because the load balancer's security group must allow inbound traffic from clients; if it blocks HTTP/HTTPS traffic, the ALB cannot forward requests and returns 503 errors. Option C is correct because an ALB has a capacity limit; once reached, it cannot handle new requests and returns 503 errors. Option D is incorrect because the stem explicitly states the target group has healthy EC2 instances, meaning registered targets exist. Option E is incorrect because the health check is functioning correctly since targets are healthy; a misconfigured health check would cause targets to be unhealthy, contradicting the given information.
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 load balancer is not attached to a subnet.
Why this is correct
Incorrect because the load balancer must be attached to subnets to function; if not, it would fail to provision, but the ALB is already running and returning 503, so this is not a likely cause.
- ✓
The security group for the load balancer is blocking traffic.
Why this is correct
Correct because the load balancer's security group must allow inbound traffic from clients. If it blocks HTTP/HTTPS traffic, the ALB cannot forward requests and returns 503 errors.
- ✓
The load balancer has reached its capacity limit.
Why this is correct
Correct because an ALB has a capacity limit; once reached, it cannot handle new requests and returns 503 errors.
- ✗
The target group has no registered targets.
Why it's wrong here
Incorrect because the stem explicitly states the target group has healthy EC2 instances, meaning registered targets exist; 'no registered targets' directly contradicts the given information.
- ✗
The target group health check is misconfigured.
Why it's wrong here
Correct because a misconfigured health check can cause the ALB to consider all targets unhealthy, even if the instances are healthy, leading to 503 errors.
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This SOA-C02 practice question is part of Courseiva's free Amazon Web Services certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the SOA-C02 exam.