DOP-C02 Resilient Cloud Solutions Practice Question
A company wants to design a resilient architecture for a web application using AWS services. Which of the following is a best practice for improving resilience?
⚠ Common exam trap
Test-takers frequently confuse database-level high availability (RDS Multi-AZ) with full application resilience, mistakenly thinking that a single-AZ compute layer is acceptable as long as the database is redundant.
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 in multiple Availability Zones.
Deploying EC2 instances across multiple Availability Zones (AZs) is a fundamental best practice for resilience because it eliminates a single point of failure at the data center level. If one AZ experiences an outage, traffic can be automatically routed to healthy instances in other AZs via an Elastic Load Balancer (ELB), ensuring application availability. This approach aligns with the AWS Well-Architected Framework's Reliability Pillar, which mandates distributing workloads across multiple AZs to achieve high availability.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Deploy EC2 instances in multiple Availability Zones.
Why this is correct
Placing EC2 instances in multiple Availability Zones (AZs) and fronting them with an Elastic Load Balancer and an Auto Scaling group ensures that if an entire AZ becomes unavailable, the load balancer can route traffic only to healthy instances in the remaining AZs. This pattern provides fault tolerance at the AZ granularity, which is the foundation of a resilient web architecture. It also allows the application to absorb a single-AZ failure without requiring any manual intervention.
- ✗
Use an Auto Scaling group in a single AZ.
Why it's wrong here
An Auto Scaling group configured to use a single Availability Zone can replace a failed instance only within that same AZ, because the group's launch configuration or launch template constrains capacity to that zone. If the AZ itself suffers an outage—such as a loss of power or network connectivity—the Auto Scaling group cannot provision instances anywhere else, so all application capacity is lost. This design protects against instance-level failures but not against AZ-level failures.
- ✗
Use a single AZ with RDS Multi-AZ.
Why it's wrong here
RDS Multi-AZ provides database high availability by maintaining a standby replica in a different Availability Zone and automatically failing over if the primary becomes unhealthy. However, the compute and web application layer remains deployed in only one AZ, so if that AZ fails, the application instances are unreachable even though the database has failed over successfully. The overall architecture is still unavailable because the front-end and application tiers are a single point of failure.
- ✗
Use one large EC2 instance to handle all traffic.
Why it's wrong here
A single large EC2 instance is a single point of failure regardless of its size or instance class; any hardware failure, scheduled maintenance event, or spot-instance interruption would take the entire application offline. Vertical scaling (choosing a larger instance type) improves performance headroom but does not provide redundancy. Without a second instance in a different AZ, there is no way to fail over traffic when the sole instance becomes unavailable.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This DOP-C02 practice question is part of Courseiva's free Amazon Web Services certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the DOP-C02 exam.