The answer is to deploy the ALB across at least two Availability Zones and use Amazon RDS Multi-AZ for the database tier. Deploying the ALB across multiple AZs ensures that traffic can be routed to healthy targets in another zone if one AZ fails, directly supporting high availability across Availability Zones for three-tier web application traffic distribution. Amazon RDS Multi-AZ enhances fault tolerance by automatically provisioning a synchronous standby replica in a different AZ, enabling automatic failover without manual intervention during an AZ outage or instance failure. On the AWS Certified Advanced Networking Specialty ANS-C01 exam, this tests your understanding of how to layer availability mechanisms across each tier—ALB for load balancing, Multi-AZ for stateful databases—and a common trap is assuming a single-AZ ALB or a non-Multi-AZ database provides sufficient resilience. Remember the memory tip: "Spread the ALB, sync the DB" to recall that both the load balancer and database must span zones for true fault tolerance.
ANS-C01 Network Design Practice Question
This ANS-C01 practice question tests your understanding of network design. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. 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 designing a network for a three-tier web application that must be highly available across multiple Availability Zones. The application uses an Application Load Balancer (ALB) for the web tier, EC2 instances for the application tier, and an Amazon RDS Multi-AZ database for the database tier. Which TWO design choices improve availability and fault tolerance?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Configure Amazon RDS Multi-AZ with a standby instance in a different Availability Zone.
Option B is correct because Amazon RDS Multi-AZ automatically provisions and maintains a synchronous standby replica in a different Availability Zone, providing automatic failover in the event of an AZ failure or database instance failure. This ensures the database tier remains available without manual intervention, directly improving fault tolerance for the three-tier application.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
Launch all EC2 instances in a single Availability Zone to reduce network latency.
Why it's wrong here
Single AZ is a single point of failure.
✓
Configure Amazon RDS Multi-AZ with a standby instance in a different Availability Zone.
Why this is correct
Provides automatic failover.
Related concept
Read the scenario before looking for a memorised answer.
✗
Use a single NAT gateway in one Availability Zone for all outbound traffic.
Read the scenario before looking for a memorised answer.
✗
Use VPC Gateway Endpoints for S3 to avoid NAT gateway costs.
Why it's wrong here
VPC endpoints are for connectivity, not fault tolerance.
Common exam traps
Common exam trap: answer the scenario, not the keyword
AWS often tests the misconception that a single NATgateway is sufficient for high availability, but the trap here is that a single NAT gateway is a single point of failure unless paired with a second NAT gateway in another AZ and route tables that direct traffic to the healthy gateway.
Detailed technical explanation
How to think about this question
Amazon RDS Multi-AZ uses synchronous replication to a standby in a different AZ, with a DNS name that automatically points to the primary; during failover, the standby is promoted with zero data loss (for supported engines) and typically completes within 1-2 minutes. The ALB, when deployed across at least two AZs, can distribute traffic and automatically reroute requests if an AZ fails, leveraging cross-zone load balancing to maintain application availability even if EC2 instances in one AZ become unhealthy.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
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
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
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.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Network Design — This question tests Network Design — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Configure Amazon RDS Multi-AZ with a standby instance in a different Availability Zone. — Option B is correct because Amazon RDS Multi-AZ automatically provisions and maintains a synchronous standby replica in a different Availability Zone, providing automatic failover in the event of an AZ failure or database instance failure. This ensures the database tier remains available without manual intervention, directly improving fault tolerance for the three-tier application.
What should I do if I get this ANS-C01 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Question Discussion
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