DOP-C02 Resilient Cloud Solutions Practice Question
A company runs a critical application on EC2 instances in an Auto Scaling group behind an ALB. They want to ensure that if an instance fails, the application remains available with minimal disruption. Which combination of services provides the best resilience?
⚠ Common exam trap
A common mix-up: candidates think a single AZ with multiple instances (Option A) or instance recovery (Option B) provides sufficient resilience, but they overlook the need for AZ-level fault isolation and integrated health-check-driven replacement that only multi-AZ Auto Scaling with ELB health checks provides.
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
✓
Auto Scaling group with ELB health checks and multiple AZs.
Deploying an Auto Scaling group across multiple Availability Zones (AZs) with Elastic Load Balancer (ALB) health checks ensures that if an EC2 instance fails in one AZ, the ALB automatically routes traffic to healthy instances in other AZs, and Auto Scaling replaces the failed instance. This combination provides both fault isolation and automated recovery, minimizing disruption to the application.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Auto Scaling group with minimum 2 in a single AZ.
Why it's wrong here
An Auto Scaling group with a minimum of two instances confined to a single Availability Zone will maintain both instances only in that one AZ. If the AZ experiences an outage, all instances fail and the ASG cannot launch replacement capacity in a different AZ because it is restricted to the sole specified availability zone. This configuration does not protect against AZ-level failures, so it fails the stated requirement of high availability.
- ✗
EC2 instance recovery with CloudWatch alarms.
Why it's wrong here
EC2 instance recovery via CloudWatch alarms automatically restarts an instance on a new host within the same Availability Zone when a hardware failure is detected, preserving its private IP address. However, this mechanism only responds to specific health checks (e.g., status check failures) and does not replace an instance that has been terminated by a user or by a spot reclamation, nor does it provide any protection if the entire AZ fails. Additionally, recovery is per-instance and gives no automatic scaling or load-balanced traffic redistribution across AZs.
- ✗
Auto Scaling group with desired capacity of 2 and a lifecycle hook.
Why it's wrong here
A lifecycle hook places instances into a wait state during launch or termination, allowing a custom script or service to perform initialization or cleanup before the action completes. This delays termination but does not independently detect workload failure and does not automatically trigger replacement of an unhealthy instance unless combined with a separate health check mechanism. With a desired capacity of two, the ASG may or may not replace instances depending on its health check settings, but the hook itself is merely a notification mechanic, not an auto-healing solution.
- ✓
Auto Scaling group with ELB health checks and multiple AZs.
Why this is correct
An Auto Scaling group spanning multiple Availability Zones and using Elastic Load Balancing health checks meets the resilience requirement: the ELB sends HTTP/HTTPS health checks to each instance, and when an instance is marked unhealthy, the ASG terminates it and launches a new one to maintain desired capacity. Multi-AZ distribution ensures that even if one AZ fails, the remaining instances continue serving traffic, and the ASG can launch replacements in other AZs. This combination provides both automated fault replacement and cross-AZ high availability.
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Same concept, more angles
2 more ways 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 runs a critical application on AWS that uses an Auto Scaling group of EC2 instances. The application must remain available even if an entire Availability Zone fails. Which THREE actions should the company take?
hard- ✓ A.Configure an ALB health check to automatically replace unhealthy instances.
- B.Use a single instance in each Availability Zone to minimize cost.
- C.Use multiple subnets in each Availability Zone for the instances.
- ✓ D.Configure the Auto Scaling group to launch instances in at least two Availability Zones.
- ✓ E.Use an Elastic Load Balancer (ELB) to distribute traffic across the instances in different AZs.
Why A: Configuring an ALB health check allows the Auto Scaling group to automatically detect and replace unhealthy instances. The ALB health check pings the instances at a specified interval (e.g., every 30 seconds) and marks them as unhealthy if they fail to respond. This triggers the Auto Scaling group to terminate the unhealthy instance and launch a new one, maintaining application availability even if an instance fails within a single AZ.
Variation 2. 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?
easy- A.Configure the Auto Scaling group to launch instances in a single Availability Zone with a desired capacity of 6.
- B.Configure the Auto Scaling group to launch instances in two Availability Zones with a desired capacity of 4.
- ✓ C.Configure the Auto Scaling group to launch instances in three Availability Zones with a desired capacity of 3.
- D.Configure the Auto Scaling group to launch instances in two Availability Zones with a desired capacity of 6, all in one AZ.
Why C: 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.
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.