- A
The target instances' security group does not allow inbound traffic from the ALB security group.
The target instances' security group must allow inbound traffic from the ALB's security group for health checks to succeed.
- B
The ALB security group does not allow outbound traffic to the targets.
Why wrong: The ALB's security group does not need to explicitly allow outbound to targets; security groups are stateful.
- C
The ALB’s security group is blocking health check traffic from the targets.
Why wrong: The ALB's security group controls inbound from clients, not inbound to targets.
- D
The target instances' security group does not allow inbound HTTP/HTTPS from the internet.
Why wrong: Target instances do not need to allow inbound from the internet directly; traffic is forwarded by the ALB.
Why ALB Health Checks Fail: Target Security Group Configuration
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: security Groups. 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 notices that traffic to an Application Load Balancer (ALB) is being rejected. The ALB has a security group that allows inbound HTTP (80) and HTTPS (443) from 0.0.0.0/0. The target group health checks are failing. What could be the issue?
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 target instances' security group does not allow inbound traffic from the ALB security group.
The issue is that the target instances' security group must allow inbound traffic from the ALB's security group (or the ALB's private IP addresses) for health checks to succeed. The ALB's security group allows inbound from 0.0.0.0/0 on ports 80/443 for client traffic, but health checks are initiated by the ALB to the targets. If the target security group does not permit this traffic, health checks fail. Option A correctly identifies this issue. Option B is incorrect because the ALB's security group does not need to explicitly allow outbound to targets; security groups are stateful. Option C is incorrect because the ALB's security group controls inbound from clients, not inbound to targets. Option D is incorrect because target instances do not need to allow inbound from the internet directly; traffic is forwarded by the ALB.
Key principle: Security Groups
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 instances' security group does not allow inbound traffic from the ALB security group.
Why this is correct
The target instances' security group must allow inbound traffic from the ALB's security group for health checks to succeed.
Related concept
Security Groups
- ✗
The ALB security group does not allow outbound traffic to the targets.
Why it's wrong here
The ALB's security group does not need to explicitly allow outbound to targets; security groups are stateful.
- ✗
The ALB’s security group is blocking health check traffic from the targets.
Why it's wrong here
The ALB's security group controls inbound from clients, not inbound to targets.
- ✗
The target instances' security group does not allow inbound HTTP/HTTPS from the internet.
Why it's wrong here
Target instances do not need to allow inbound from the internet directly; traffic is forwarded by the ALB.
Common exam traps
Common exam trap: answer the scenario, not the keyword
A common mistake is to focus on the ALB's security group inbound rules, but the actual issue is the target security group not allowing traffic from the ALB.
Detailed technical explanation
How to think about this question
Treat this as a scenario question. Identify the problem, the constraint, and the best action. Then compare each option against those facts.
KKey Concepts to Remember
- Security Groups
- ALB Health Checks
- Target Group
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
Security Groups
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 security Groups, 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 — Security Groups.
What is the correct answer to this question?
The correct answer is: The target instances' security group does not allow inbound traffic from the ALB security group. — The issue is that the target instances' security group must allow inbound traffic from the ALB's security group (or the ALB's private IP addresses) for health checks to succeed. The ALB's security group allows inbound from 0.0.0.0/0 on ports 80/443 for client traffic, but health checks are initiated by the ALB to the targets. If the target security group does not permit this traffic, health checks fail. Option A correctly identifies this issue. Option B is incorrect because the ALB's security group does not need to explicitly allow outbound to targets; security groups are stateful. Option C is incorrect because the ALB's security group controls inbound from clients, not inbound to targets. Option D is incorrect because target instances do not need to allow inbound from the internet directly; traffic is forwarded by the ALB.
What should I do if I get this SOA-C02 question wrong?
Review security Groups, then practise related SOA-C02 questions on the same topic to reinforce the concept.
What is the key concept behind this question?
Security Groups
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Last reviewed: Jun 20, 2026
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