← SOA-C02·Amazon Web Services

Question 1,126 of 1,546

Reliability and Business Continuity →mediumMultiple ChoiceObjective-mapped

Quick Answer

The correct answer is to ensure the Auto Scaling group launches instances in both Availability Zones and configure the Application Load Balancer with cross-zone load balancing enabled. This directly improves application high availability across availability zones by distributing the EC2 instance fleet so that if one AZ fails, the ALB can route traffic exclusively to healthy instances in the remaining AZ, keeping the application online without altering the existing Aurora database cluster. On the AWS Certified SysOps Administrator Associate SOA-C02 exam, this scenario tests your understanding of the shared responsibility model for high availability—specifically that the application tier must be architected for AZ failure independently of the database tier, which already has Multi-AZ resilience built into Aurora. A common trap is assuming you need to add a second VPC or a cross-region read replica, but those are costly overkill for a single-region AZ failure. Memory tip: think “spread the compute, keep the data” — distribute your EC2 instances across AZs, and let the ALB’s cross-zone balancing handle the traffic reroute.

SOA-C02 Reliability and Business Continuity Practice Question

This SOA-C02 practice question tests your understanding of reliability and business continuity. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. 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 has a production AWS account with a single VPC and multiple subnets across two Availability Zones. The company hosts a web application on EC2 instances in an Auto Scaling group. The application uses an Amazon Aurora MySQL database cluster with one writer and two reader instances in the same VPC. The SysOps administrator configured AWS CloudTrail to log API calls and Amazon CloudWatch alarms for operational monitoring. After a recent network partition event in one Availability Zone, the application became unavailable for several minutes. The administrator wants to improve the application's resilience to such events without changing the database cluster configuration. The administrator has budget for additional resources but wants to minimize costs. What should the administrator do?

Clue words in this question

Noticing these words before you look at the options changes how you read each choice.

Clue: "minimum / minimize"
Why it matters: Asks for the least resource use — fewest addresses, smallest subnet, lowest overhead. Eliminate over-provisioned options even if they would technically work.

Question 1mediummultiple choice

Review the full subnetting walkthrough →

A
Enable Multi-AZ for the Aurora cluster, which is already enabled by default. Additionally, increase the instance size of the writer instance.
Why wrong: Multi-AZ is already inherent in Aurora. Increasing instance size does not improve resilience to AZ failure.
B
Configure a cross-region read replica for the Aurora cluster and promote it to primary if the primary AZ fails.
Why wrong: Cross-region read replica does not help with AZ failure within the same region; it is for regional failure.
C
Create a second VPC in a different AWS Region and set up a second Aurora cluster. Use Route 53 with failover routing to direct traffic to the secondary region if the primary fails.
Why wrong: This is a multi-region DR solution, which is overkill and costly for an AZ failure scenario.
D
Ensure the Auto Scaling group launches instances in both Availability Zones. Configure the Application Load Balancer to be cross-zone load balancing enabled.
This distributes traffic across AZs, so if one AZ fails, the ALB routes to the other AZ's instances.

Full breakdown with real-world context →

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

✓

Ensure the Auto Scaling group launches instances in both Availability Zones. Configure the Application Load Balancer to be cross-zone load balancing enabled.

Option C is correct because distributing EC2 instances across multiple AZs and configuring the ALB as cross-zone enabled ensures that traffic is routed to healthy instances in any AZ. This provides high availability for the application tier without changing the database. Option A is wrong because adding a second VPC with its own database cluster would be expensive and complex. Option B is wrong because creating a read replica in another region does not help with AZ failure within the same region. Option D is wrong because Multi-AZ for Aurora is already inherent; the database cluster already has instances in multiple AZs by design.

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.

✗
Enable Multi-AZ for the Aurora cluster, which is already enabled by default. Additionally, increase the instance size of the writer instance.
Why it's wrong here
Multi-AZ is already inherent in Aurora. Increasing instance size does not improve resilience to AZ failure.
✗
Configure a cross-region read replica for the Aurora cluster and promote it to primary if the primary AZ fails.
Why it's wrong here
Cross-region read replica does not help with AZ failure within the same region; it is for regional failure.
✗
Create a second VPC in a different AWS Region and set up a second Aurora cluster. Use Route 53 with failover routing to direct traffic to the secondary region if the primary fails.
Why it's wrong here
This is a multi-region DR solution, which is overkill and costly for an AZ failure scenario.
✓
Ensure the Auto Scaling group launches instances in both Availability Zones. Configure the Application Load Balancer to be cross-zone load balancing enabled.
Why this is correct
This distributes traffic across AZs, so if one AZ fails, the ALB routes to the other AZ's instances.
Clue confirmation
The clue word "minimum / minimize" in the question point toward this answer.
Related concept
CIDR notation defines the prefix length.

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.

Trap categories for this question

Scenario analysis trap
This is a multi-region DR solution, which is overkill and costly for an AZ failure scenario.

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 startup's cloud architect reviews their monthly bill and notices costs are higher than expected for a long-running batch job. Switching from on-demand instances to Reserved Instances — or using Spot/Preemptible VMs — can reduce compute costs by up to 72 %. Questions like this test whether you understand the tradeoffs between commitment, flexibility, and cost across cloud pricing models.

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.

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FAQ

Questions learners often ask

What does this SOA-C02 question test?

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: Ensure the Auto Scaling group launches instances in both Availability Zones. Configure the Application Load Balancer to be cross-zone load balancing enabled. — Option C is correct because distributing EC2 instances across multiple AZs and configuring the ALB as cross-zone enabled ensures that traffic is routed to healthy instances in any AZ. This provides high availability for the application tier without changing the database. Option A is wrong because adding a second VPC with its own database cluster would be expensive and complex. Option B is wrong because creating a read replica in another region does not help with AZ failure within the same region. Option D is wrong because Multi-AZ for Aurora is already inherent; the database cluster already has instances in multiple AZs by design.

What should I do if I get this SOA-C02 question wrong?

Are there clue words in this question I should notice?

Yes — watch for: "minimum / minimize". Asks for the least resource use — fewest addresses, smallest subnet, lowest overhead. Eliminate over-provisioned options even if they would technically work.

What is the key concept behind this question?

CIDR notation defines the prefix length.

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Last reviewed: Jun 20, 2026

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