DOP-C02 Resilient Cloud Solutions Practice Question
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.)
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
✓
Launch EC2 instances in at least two Availability Zones
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.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
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Use a single large EC2 instance to simplify management
Why it's wrong here
A single large EC2 instance, regardless of instance size, is a single point of failure. If the underlying physical host fails, the instance can't be restarted automatically, and if the entire Availability Zone experiences an outage, the application becomes unreachable. Vertical scaling also hits hard limits, and maintenance or patching typically requires downtime. True fault tolerance requires redundant instances spread across at least two Availability Zones.
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Deploy multiple Application Load Balancers in each AZ
Why it's wrong here
An Application Load Balancer is a regional, Layer 7 service that can route traffic to targets in multiple Availability Zones by simply attaching subnets in those AZs to the ELB. Deploying separate ALBs in each Availability Zone is redundant, expensive, and adds management overhead, and doesn't improve fault tolerance because the ALB itself already spans AZs and is designed to be highly available. In fact, using multiple ALBs can complicate DNS routing, health checks, and cross-zone load balancing without any benefit.
- ✓
Launch EC2 instances in at least two Availability Zones
Why this is correct
Launching EC2 instances in at least two Availability Zones is the foundational principle for highly available web server fleets. Availability Zones are physically separate data centers with independent power, cooling, and networking, so a failure in one AZ does not affect the other. Combined with a load balancer that spans those same AZs, traffic automatically continues to be served by healthy instances if one AZ loses capacity. This design eliminates the single-AZ dependency and is a core requirement for fault-tolerant compute tiers.
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Use an RDS Multi-AZ deployment for the web server fleet
Why it's wrong here
RDS Multi-AZ is a database-specific feature that provides a synchronous standby replica of an Amazon RDS instance in a different Availability Zone for automatic failover of the database tier. It has no relevance to EC2-based web servers, which are compute resources running your application code, not managed database instances. Deploying RDS Multi-AZ as a substitute for EC2 instance redundancy is a category error and would not improve the high availability of your web application layer; it only protects the data tier.
- ✓
Use an Auto Scaling group to replace failed instances automatically
Why this is correct
An Auto Scaling group is the correct mechanism to automatically replace failed or unhealthy EC2 instances, preserving the desired capacity of your web server fleet. It integrates with Elastic Load Balancing health checks and can terminate an instance that fails to pass them, then launch a fresh instance to maintain the configured count. This self-healing behavior works across multiple Availability Zones when the ASG is configured with subnets in each AZ, directly supporting fault tolerance and reducing manual intervention during infrastructure disruptions.
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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.