- 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. A key principle to apply: auto Scaling groups can distribute EC2 instances across multiple Availability Zones.. 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 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.
Key principle: Auto Scaling groups can distribute EC2 instances across multiple Availability Zones.
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
Auto Scaling groups can distribute EC2 instances across multiple Availability Zones.
- ✗
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
Auto Scaling groups can distribute EC2 instances across multiple Availability Zones.
- ✗
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 confuse a read replica (which is for read scaling and requires manual promotion) with a Multi-AZ standby (which provides automatic failover for high availability).
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. Auto Scaling groups distribute instances across AZs by defining multiple subnets in the launch configuration; the load balancer health checks automatically route traffic only to healthy instances. This combination ensures both compute and database layers survive a single-AZ outage without manual intervention.
KKey Concepts to Remember
- Auto Scaling groups can distribute EC2 instances across multiple Availability Zones.
- Application Load Balancers are inherently multi-AZ and distribute traffic to healthy targets.
- RDS Multi-AZ provides synchronous replication and automatic failover for databases.
- Multi-AZ deployments protect against single Availability Zone outages for both compute and data.
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
Auto Scaling groups can distribute EC2 instances across multiple Availability Zones.
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 auto Scaling groups can distribute EC2 instances across multiple Availability Zones., then practise related SAA-C03 questions on the same topic to reinforce the concept.
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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 — Auto Scaling groups can distribute EC2 instances across multiple Availability Zones..
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 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.
What should I do if I get this SAA-C03 question wrong?
Review auto Scaling groups can distribute EC2 instances across multiple Availability Zones., then practise related SAA-C03 questions on the same topic to reinforce the concept.
What is the key concept behind this question?
Auto Scaling groups can distribute EC2 instances across multiple Availability Zones.
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Last reviewed: Jun 11, 2026
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