SOA-C02 Reliability and Business Continuity Practice Question
This SOA-C02 practice question tests your understanding of reliability and business continuity. 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) is returning 503 errors to clients. The target group has healthy EC2 instances. Which THREE possible causes should the administrator investigate? (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 security group for the load balancer is blocking traffic.
Options A, B, and D are correct. An ALB returns 503 if no healthy targets are registered, if the load balancer is at capacity, or if there is a misconfigured security group blocking traffic. Option C is wrong because an unhealthy target group would show unhealthy instances. Option E is wrong because a missing subnet would prevent the ALB from being created or functioning, but the ALB is already working.
Key principle: Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
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 it's wrong here
ALB requires subnets to be created.
✓
The security group for the load balancer is blocking traffic.
Why this is correct
Can cause 503 if inbound/outbound rules are wrong.
Common exam trap: usable hosts are not the same as total addresses
Subnetting questions often tempt you into counting all addresses. In normal IPv4 subnets, the network and broadcast addresses are not usable host addresses.
Trap categories for this question
Command / output trap
Would show unhealthy targets, not 503.
Detailed technical explanation
How to think about this question
Subnetting questions test whether you can identify the network, broadcast address, usable range, mask and correct subnet. Slow down enough to calculate the block size correctly.
KKey Concepts to Remember
CIDR notation defines the prefix length.
Block size helps identify subnet boundaries.
Network and broadcast addresses are not usable hosts in normal IPv4 subnets.
The required host count determines the smallest suitable subnet.
TExam Day Tips
→Write the block size before choosing the subnet.
→Check whether the question asks for hosts, subnets or a specific address range.
→Do not confuse /24, /25, /26 and /27 host counts.
Key takeaway
Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
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 block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related SOA-C02 subnetting questions on CIDR, address ranges, and subnet selection.
Reliability and Business Continuity — This question tests Reliability and Business Continuity — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: The security group for the load balancer is blocking traffic. — Options A, B, and D are correct. An ALB returns 503 if no healthy targets are registered, if the load balancer is at capacity, or if there is a misconfigured security group blocking traffic. Option C is wrong because an unhealthy target group would show unhealthy instances. Option E is wrong because a missing subnet would prevent the ALB from being created or functioning, but the ALB is already working.
What should I do if I get this SOA-C02 question wrong?
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related SOA-C02 subnetting questions on CIDR, address ranges, and subnet selection.
What is the key concept behind this question?
CIDR notation defines the prefix length.
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Question Discussion
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