DOP-C02 Resilient Cloud Solutions Practice Question
A development team wants to ensure that their application can continue serving traffic even if an entire AWS Availability Zone (AZ) becomes unavailable. The application runs on Amazon EC2 instances in an Auto Scaling group and uses an Application Load Balancer (ALB). Which configuration should the team implement to meet this requirement?
⚠ Common exam trap
A common mix-up: candidates confuse instance-level resilience (e.g., replacing unhealthy instances) with AZ-level resilience, or they think that multiple instances in a single AZ provide sufficient fault tolerance, ignoring the fact that an AZ failure takes down all instances in that AZ.
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 EC2 instances across multiple AZs, and ensure the ALB is enabled for cross-zone load balancing.
Deploying EC2 instances across multiple Availability Zones (AZs) ensures that if one AZ fails, the remaining AZs continue to serve traffic. Enabling cross-zone load balancing on the ALB distributes incoming requests evenly across all healthy instances in all AZs, preventing traffic from being sent only to instances in the same AZ as the client. This architecture meets the requirement for high availability and fault tolerance at the AZ level.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Configure the Auto Scaling group to launch EC2 instances across multiple AZs, and ensure the ALB is enabled for cross-zone load balancing.
Why this is correct
By configuring the Auto Scaling group to span multiple Availability Zones and enabling cross-zone load balancing on the ALB, the application can survive an entire AZ failure. If one AZ becomes unavailable, the ALB routes traffic only to the remaining healthy targets, while the ASG automatically launches replacement instances in the other AZs to maintain capacity. Cross-zone load balancing ensures that traffic is distributed evenly across all instances, even when one AZ has fewer instances. This design provides both redundancy and optimal utilization.
- ✗
Use a launch template with multiple instance types to ensure diversity across the fleet.
Why it's wrong here
Using a launch template with multiple instance types diversifies the underlying hardware and can improve capacity acquisition for Spot Instances, but it does not address Availability Zone failure. If all instances are launched in a single AZ, a failure of that AZ will take down every instance regardless of instance type. Instance type diversity is a cost and scaling strategy, not an availability or fault-tolerance mechanism for AZ-level outages.
- ✗
Use a single AZ but configure EC2 Auto Scaling to replace unhealthy instances automatically.
Why it's wrong here
Configuring Auto Scaling to replace unhealthy instances within a single Availability Zone can handle individual instance failures, such as hardware faults or crashes, by terminating and relaunching them. However, it cannot protect against an Availability Zone failure, because the replacement instances are launched in the same AZ and will likely be affected by the same outage, such as a network partition or power loss. Moreover, the ASG itself may be unable to launch new instances if the AZ's capacity is impaired, leaving the application completely unavailable.
- ✗
Launch all EC2 instances in the same AZ to minimize latency, and configure the Auto Scaling group to maintain a minimum of two instances.
Why it's wrong here
Launching all instances in the same Availability Zone and maintaining a minimum of two instances provides instance-level redundancy, so the application can continue if one instance fails and is replaced. But this design remains a single point of failure: if the entire AZ becomes unavailable—for example, due to a natural disaster or regional network issue—both instances are unreachable and the ASG cannot restore service elsewhere. High availability requires distributing instances across multiple geographically isolated AZs, not just having multiple instances in one location.
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Same concept, more angles
1 more way this is tested on DOP-C02
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 wants to design a highly available and fault-tolerant architecture for a stateless web application on AWS. Which TWO actions should they take? (Choose two.)
easy- A.Use a single large EC2 instance to simplify management
- B.Deploy multiple Application Load Balancers in each AZ
- ✓ C.Launch EC2 instances in at least two Availability Zones
- D.Use an RDS Multi-AZ deployment for the web server fleet
- ✓ E.Use an Auto Scaling group to replace failed instances automatically
Why C: To achieve high availability and fault tolerance for a stateless web application, you should deploy EC2 instances in at least two Availability Zones (C) to eliminate a single point of failure, and use an Auto Scaling group (E) to automatically replace failed instances and maintain desired capacity. Option A is incorrect because a single large instance is a single point of failure and does not provide fault tolerance. Option B is incorrect because multiple Application Load Balancers per AZ are unnecessary; a single ALB can route traffic across multiple AZs. Option D is incorrect because RDS Multi-AZ is a database feature, not for the web server fleet.
JA
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.