The correct answer is to use an Auto Scaling group with a minimum of two instances distributed across two Availability Zones with a 'balanced best effort' strategy. This configuration ensures high availability across Availability Zones because it maintains at least one healthy instance in each zone, so if one zone fails, the other continues serving traffic without interruption. On the AWS Certified Solutions Architect Professional SAP-C02 exam, this scenario tests your understanding of how Auto Scaling group distribution policies interact with fault isolation—the common trap is assuming a single instance per zone with a minimum of one is sufficient, but that allows scaling to zero, breaking availability. A key memory tip is to think "minimum of two, one per zone, balanced best effort" as the trifecta for zone-level resilience.
SAP-C02 Practice Question: Accelerate Workload Migration and Modernization
This SAP-C02 practice question tests your understanding of accelerate workload migration and modernization. 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 company is migrating a critical application to AWS. The application must be highly available across two Availability Zones. The migration plan includes rehosting the application on EC2 instances in an Auto Scaling group behind an ALB. Which configuration ensures that the application remains available during an Availability Zone failure?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Use an Auto Scaling group with a minimum of 2 across two Availability Zones, with a distribution strategy of 'balanced best effort'
Option D is correct because spreading instances across two AZs with a minimum of one per AZ ensures that if one AZ fails, the other still has capacity. Option A is wrong because a single AZ does not provide AZ-level fault tolerance. Option B is wrong because a single instance per AZ with a minimum of 1 would allow scaling down to 0. Option C is wrong because placing all instances in one subnet is a single point of failure.
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.
✓
Use an Auto Scaling group with a minimum of 2 across two Availability Zones, with a distribution strategy of 'balanced best effort'
Why this is correct
Auto Scaling group with minimum 2 across two AZs ensures at least one instance per AZ.
Use an Auto Scaling group with a minimum of 1 and maximum of 10 across two AZs
Why it's wrong here
Minimum of 1 could result in all instances in one AZ if the other AZ fails to launch.
✗
Launch instances in a single Availability Zone with multiple subnets
Why it's wrong here
Single AZ is not resilient to AZ failure.
✗
Launch instances in two Availability Zones but place all instances in the same subnet
Why it's wrong here
Subnets are tied to AZs; cannot span AZs.
Common exam traps
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.
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
An e-commerce site experiences heavy traffic on Black Friday and near-zero traffic during off-peak weeks. Rather than provisioning permanent large VMs, the team uses auto-scaling groups that add capacity automatically under load and reduce it overnight. Questions like this test whether you understand elasticity, availability zones, and cloud compute scaling patterns.
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 SAP-C02 subnetting questions on CIDR, address ranges, and subnet selection.
Accelerate Workload Migration and Modernization — This question tests Accelerate Workload Migration and Modernization — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: Use an Auto Scaling group with a minimum of 2 across two Availability Zones, with a distribution strategy of 'balanced best effort' — Option D is correct because spreading instances across two AZs with a minimum of one per AZ ensures that if one AZ fails, the other still has capacity. Option A is wrong because a single AZ does not provide AZ-level fault tolerance. Option B is wrong because a single instance per AZ with a minimum of 1 would allow scaling down to 0. Option C is wrong because placing all instances in one subnet is a single point of failure.
What should I do if I get this SAP-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 SAP-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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