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Quick Answer
The answer is deploying EC2 instances across at least two Availability Zones, using Amazon RDS Multi-AZ, and storing session data in ElastiCache for Redis with replication across two AZs. These three choices work together because they eliminate single points of failure at the AZ level: the ALB distributes traffic to healthy EC2 instances in surviving AZs, RDS Multi-AZ provides automatic failover to a standby in a different AZ, and ElastiCache with cross-AZ replication ensures session state persists even if the primary cache node goes down. On the SAA-C03 exam, this scenario tests your understanding of stateless application design and the difference between high availability and disaster recovery—a common trap is assuming a single-AZ ElastiCache cluster is sufficient, but without replication across AZs, a failure would wipe out all session data. Memory tip: think of the three pillars of AZ resilience—compute (EC2 across AZs), database (RDS Multi-AZ), and state (ElastiCache cross-AZ replication).
SAA-C03 Design Resilient Architectures Practice Question
This SAA-C03 practice question tests your understanding of design resilient architectures. 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 designing a highly available web application on AWS. The application runs on Amazon EC2 instances behind an Application Load Balancer (ALB) and uses an Amazon RDS Multi-AZ DB instance. Which three design choices would improve the application's resilience against an AWS Availability Zone failure? (Choose three.)
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
✓
Deploy EC2 instances across at least two Availability Zones in the same AWS Region.
Deploying EC2 instances across at least two Availability Zones (AZs) ensures that if one AZ fails, the ALB can route traffic to healthy instances in the other AZ, maintaining application availability. This is a fundamental pattern for building resilient architectures on AWS, as it eliminates the single point of failure at the AZ level.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often confuse AZ-level failures with Regional failures and incorrectly select cross-Region solutions like Route 53 failover routing, which is unnecessary and adds latency for an AZ-level scenario.
Detailed technical explanation
How to think about this question
Amazon RDS Multi-AZ deployment automatically synchronously replicates data to a standby instance in a different AZ and provides automatic failover with a typical DNS change time of 60-120 seconds, ensuring database resilience without manual intervention. ElastiCache for Redis with replication across two AZs uses a primary node in one AZ and a replica in another; if the primary AZ fails, Redis automatically promotes the replica, maintaining session state continuity. Both services rely on synchronous replication (RDS) or asynchronous replication (Redis) to minimize data loss during failover.
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
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.
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FAQ
Questions learners often ask
What does this SAA-C03 question test?
Design Resilient Architectures — This question tests Design Resilient Architectures — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Deploy EC2 instances across at least two Availability Zones in the same AWS Region. — Deploying EC2 instances across at least two Availability Zones (AZs) ensures that if one AZ fails, the ALB can route traffic to healthy instances in the other AZ, maintaining application availability. This is a fundamental pattern for building resilient architectures on AWS, as it eliminates the single point of failure at the AZ level.
What should I do if I get this SAA-C03 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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Same concept, more angles
3 more ways this is tested on SAA-C03
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. A company is deploying a stateless web application on Amazon ECS with Fargate. The application must be resilient to individual task failures and Availability Zone failures. Which three steps should the company take to achieve this resilience? (Choose three.)
medium- ✓ .Configure the ECS service to use a spread placement strategy across Availability Zones.
- ✓ .Set a minimum healthy percent of 50 and a maximum percent of 200 in the ECS service deployment configuration.
- .Place all ECS tasks in a single subnet to minimize network latency.
- ✓ .Use an Application Load Balancer (ALB) in front of the ECS service to distribute traffic across tasks.
- .Store application session data in an attached EFS file system shared across all tasks.
- .Disable automatic task replacement to avoid unnecessary task churn during failures.
Why : Configuring the ECS service with a spread placement strategy across Availability Zones ensures tasks are distributed across multiple AZs, providing resilience against AZ failures. Setting a minimum healthy percent of 50 and a maximum percent of 200 allows the service to maintain at least half of the desired tasks during deployments or failures while scaling up to replace failed tasks without downtime. Using an Application Load Balancer (ALB) in front of the ECS service distributes incoming traffic across healthy tasks in different AZs, automatically rerouting traffic if a task or AZ fails.
Variation 2. A retail API runs on Amazon EC2 instances behind an Application Load Balancer and stores orders in an Amazon RDS for PostgreSQL database. A test that stopped one Availability Zone caused the API to return errors because all application servers were in the same AZ and the database was single-AZ. Which two changes should the architect make to continue serving traffic during a single-AZ failure? Select two.
medium- A.Increase the EC2 instance size and keep all application servers in the same subnet.
- ✓ B.Configure the Auto Scaling group to launch instances across private subnets in at least two Availability Zones.
- C.Replace the Application Load Balancer with a Network Load Balancer in a single Availability Zone.
- ✓ D.Convert the RDS for PostgreSQL database to a Multi-AZ deployment.
- E.Add an Amazon RDS read replica and point the application to the replica endpoint.
Why B: Option B is correct because distributing EC2 instances across multiple Availability Zones via an Auto Scaling group ensures that if one AZ fails, the remaining AZs continue to serve traffic. Option D is correct because converting the RDS for PostgreSQL database to a Multi-AZ deployment provides a standby replica in a different AZ, enabling automatic failover and continued database availability during a single-AZ failure.
Variation 3. A retail API runs on Amazon EC2 instances behind an Application Load Balancer and stores orders in an Amazon RDS for PostgreSQL database. A test that stopped one Availability Zone caused the API to return errors because all application servers were in the same AZ and the database was single-AZ. Which two changes should the architect make to continue serving traffic during a single-AZ failure? Select two.
medium- A.Increase the EC2 instance size and keep all application servers in the same subnet.
- ✓ B.Configure the Auto Scaling group to launch instances across private subnets in at least two Availability Zones.
- C.Replace the Application Load Balancer with a Network Load Balancer in a single Availability Zone.
- ✓ D.Convert the RDS for PostgreSQL database to a Multi-AZ deployment.
- E.Add an Amazon RDS read replica and point the application to the replica endpoint.
Why B: Option B is correct because distributing EC2 instances across private subnets in at least two Availability Zones (AZs) ensures that if one AZ fails, the Auto Scaling group can continue serving traffic from instances in the remaining AZs. This eliminates the single point of failure for the application tier. Option D is correct because converting the RDS for PostgreSQL database to a Multi-AZ deployment automatically provisions a standby replica in a different AZ, enabling automatic failover during an AZ outage and preserving database availability.
Last reviewed: Jun 11, 2026
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