- A
Increase the EC2 instance size and keep all application servers in the same subnet.
Why wrong: Bigger instances add capacity, but they do not protect against the entire Availability Zone becoming unavailable.
- B
Configure the Auto Scaling group to launch instances across private subnets in at least two Availability Zones.
Spreading the application tier across multiple AZs preserves healthy capacity if one AZ fails and lets the load balancer keep serving requests.
- C
Replace the Application Load Balancer with a Network Load Balancer in a single Availability Zone.
Why wrong: A single-AZ load balancer still leaves the application vulnerable to an AZ outage and does not add redundant capacity.
- D
Convert the RDS for PostgreSQL database to a Multi-AZ deployment.
Multi-AZ RDS adds synchronous standby failover in another AZ, which protects the writer database from a single-AZ loss.
- E
Add an Amazon RDS read replica and point the application to the replica endpoint.
Why wrong: Read replicas help with read scaling, but they are not a direct replacement for automatic writer failover in this scenario.
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 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.
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
Configure the Auto Scaling group to launch instances across private subnets in at least two Availability Zones.
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.
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.
- ✗
Increase the EC2 instance size and keep all application servers in the same subnet.
Why it's wrong here
Bigger instances add capacity, but they do not protect against the entire Availability Zone becoming unavailable.
- ✓
Configure the Auto Scaling group to launch instances across private subnets in at least two Availability Zones.
Why this is correct
Spreading the application tier across multiple AZs preserves healthy capacity if one AZ fails and lets the load balancer keep serving requests.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Replace the Application Load Balancer with a Network Load Balancer in a single Availability Zone.
Why it's wrong here
A single-AZ load balancer still leaves the application vulnerable to an AZ outage and does not add redundant capacity.
- ✓
Convert the RDS for PostgreSQL database to a Multi-AZ deployment.
Why this is correct
Multi-AZ RDS adds synchronous standby failover in another AZ, which protects the writer database from a single-AZ loss.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Add an Amazon RDS read replica and point the application to the replica endpoint.
Why it's wrong here
Read replicas help with read scaling, but they are not a direct replacement for automatic writer failover in this scenario.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often think a read replica can serve as a high-availability solution for writes, but read replicas are asynchronous and do not support automatic failover for the primary database.
Trap categories for this question
Scenario analysis trap
Read replicas help with read scaling, but they are not a direct replacement for automatic writer failover in this scenario.
Detailed technical explanation
How to think about this question
Multi-AZ RDS deployments use synchronous replication to a standby instance in a different AZ, with automatic failover typically completing within 60–120 seconds. For the application tier, an Auto Scaling group with a multi-AZ launch configuration distributes instances across subnets, and the ALB automatically routes traffic only to healthy targets in remaining AZs. A common real-world scenario is a regional power outage affecting one AZ; without both changes, the API would be completely unavailable.
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 media company stores terabytes of video archives that are accessed once a year for audit purposes. Moving these objects to a cold storage tier (Azure Archive, S3 Glacier, or Google Nearline) costs a fraction of hot storage. Questions like this test whether you understand storage tiers, access frequency tradeoffs, and retrieval latency requirements.
What to study next
Got this wrong? Here's your next step.
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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: Configure the Auto Scaling group to launch instances across private subnets in at least two Availability Zones. — 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.
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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Last reviewed: Jun 11, 2026
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