Automatic Instance Replacement Using ALB Health Checks
A company runs a web application on EC2 instances behind an ALB. To improve resilience, they want to automatically replace failed instances and maintain a minimum number of instances. Which AWS service should be used?
⚠ Common exam trap
DOP-C02 often tests the misconception that CloudFormation or Elastic Beanstalk 'does' auto scaling, when in fact Auto Scaling is the underlying service and the others merely orchestrate it — candidates must pick the service that directly provides the capability.
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
✓
Amazon EC2 Auto Scaling
Amazon EC2 Auto Scaling is purpose-built to maintain a desired/minimum number of instances and automatically replace unhealthy ones via health checks integrated with ELB. It continuously monitors instance health and launches replacements when instances fail, ensuring the minimum capacity is preserved. This directly satisfies the resilience requirement without manual intervention.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Amazon EC2 Auto Scaling
Why this is correct
Amazon EC2 Auto Scaling is the service that continuously monitors the health of EC2 instances using EC2 status checks and, when configured, Elastic Load Balancing health checks. If an instance fails these checks, Auto Scaling automatically terminates it and launches a replacement instance to maintain the desired or minimum fleet size. This health-based replacement is an inherent capability of an Auto Scaling group, making it the correct answer for automatically replacing unhealthy instances.
- ✗
AWS CloudFormation
Why it's wrong here
AWS CloudFormation is an infrastructure as code (IaC) service that provisions and manages resources by creating, updating, and deleting stacks based on a template. While CloudFormation can launch Auto Scaling groups and other resources, it does not continuously monitor instance health or react to failures. Once resources are created, CloudFormation's lifecycle management is event-driven only via stack operations, not by replacing failed EC2 instances, so it cannot perform automatic replacement on its own.
- ✗
AWS Elastic Beanstalk
Why it's wrong here
AWS Elastic Beanstalk is a Platform as a Service (PaaS) that abstracts the underlying EC2 infrastructure, and underneath it uses Auto Scaling groups to manage capacity. However, Elastic Beanstalk is not the service you directly configure to replace instances; it handles environments as a whole, and its replacement behavior is tied to environment updates or health-based rotations managed by its internal components. The question asks for the service responsible for automatic replacement, and that responsibility belongs to the Auto Scaling group, not to Elastic Beanstalk itself.
- ✗
AWS Systems Manager
Why it's wrong here
AWS Systems Manager is a management and automation service designed for operations such as patching, inventory, parameter management, and running commands or automation documents. It does not monitor the health of EC2 instances for the purpose of replacing them, nor does it manage fleet capacity. While Systems Manager can execute scripts or automations to recover instances, it lacks the built-in, automatic health-check-driven replacement loop that Auto Scaling provides, so it is not the appropriate service for this scenario.
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JA
Written and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed September 2026 · checked against the official Amazon Web Services exam blueprint
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.