DOP-C02 Resilient Cloud Solutions Practice Question
A company runs a stateless web application on EC2 instances in an Auto Scaling group across three Availability Zones. The application uses an Application Load Balancer. The operations team needs to ensure that the application remains available if one AZ fails. Which solution is MOST resilient?
⚠ Common exam trap
Test-takers frequently think using two AZs is sufficient for high availability, but the question specifically asks for the 'MOST resilient' solution, and three AZs provide better fault isolation and recovery capacity than two, especially when the desired capacity is low.
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 in three Availability Zones with a desired capacity of 3.
Distributing instances across three Availability Zones (AZs) with a desired capacity of 3 ensures that even if one AZ fails, the remaining two AZs still have at least 2 instances running, maintaining service capacity. The Application Load Balancer (ALB) automatically routes traffic away from the failed AZ, and the Auto Scaling group will replace lost instances in the healthy AZs, providing the highest resilience against a single-AZ failure.
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 instances in a single Availability Zone with a desired capacity of 6.
Why it's wrong here
If that Availability Zone fails, all six instances become unavailable, causing a complete outage of the stateless web application. The Auto Scaling group cannot launch replacement instances in other zones because it is confined to a single AZ, so there is no automatic failover. Even with a desired capacity of six, every instance shares the same failure domain, so the additional capacity does not improve resilience.
- ✗
Configure the Auto Scaling group to launch instances in two Availability Zones with a desired capacity of 4.
Why it's wrong here
With a desired capacity of four spread across two Availability Zones, each AZ typically runs two instances, so a single AZ failure removes 50% of your serving capacity. The remaining AZ may not have spare capacity to launch replacements, and the ASG's rebalancing could be delayed or fail if that AZ is constrained. A three-AZ design with one instance per AZ would preserve two-thirds of capacity, making this two-AZ setup unnecessarily risky for production traffic.
- ✓
Configure the Auto Scaling group to launch instances in three Availability Zones with a desired capacity of 3.
Why this is correct
Configuring three Availability Zones with a desired capacity of three places one instance in each AZ, so if any single AZ fails, the remaining two instances continue serving traffic, preserving 66% of capacity. The Auto Scaling group will automatically detect the unhealthy instances and launch replacements in other healthy AZs, gradually restoring capacity to the desired level. Because the application is stateless, a load balancer can distribute traffic across the surviving instances, providing high availability with minimal disruption.
- ✗
Configure the Auto Scaling group to launch instances in two Availability Zones with a desired capacity of 6, all in one AZ.
Why it's wrong here
Placing all instances in one Availability Zone, even while specifying two AZs in the ASG configuration, completely defeats the purpose of multi-AZ deployment because a failure of that single AZ takes down the entire fleet. This situation often results from a misconfiguration, such as a launch template that only references subnets from one AZ, or from not redistributing instances across the configured zones. Regardless of the desired capacity of six, the architecture remains a single point of failure and cannot provide the promised resilience.
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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.