DOP-C02 Resilient Cloud Solutions Practice Question
A company runs a web application on EC2 instances behind an Application Load Balancer. The application experiences intermittent failures due to a single Availability Zone failing. Which solution is MOST resilient and cost-effective?
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
✓
Deploy EC2 instances across two Availability Zones and configure the ALB to distribute traffic
Most resilient and cost-effective. Deploying EC2 instances across two Availability Zones and configuring the ALB to distribute traffic ensures high availability by handling a single AZ failure without over-provisioning. Option A is wrong because using a larger instance in the same AZ does not address AZ failure. Option B is wrong because using three AZs with a single instance each and a Network Load Balancer is more expensive and not necessary for this scenario; ALB already supports cross-zone load balancing. Option C is wrong because migrating to a different region adds latency, complexity, and cost.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Use a larger instance type in the same Availability Zone
Why it's wrong here
Scaling vertically to a larger instance type within the same Availability Zone does nothing to eliminate the single point of failure represented by that AZ. If the AZ experiences an outage, or a hardware failure impacts that specific instance, the application becomes unavailable regardless of the instance's size. High availability requires redundancy across independent failure domains, not simply more compute capacity in the same location.
- ✗
Use an Auto Scaling group with a single instance in each of three Availability Zones and a Network Load Balancer
Why it's wrong here
Using a Network Load Balancer introduces an unnecessary Layer 4 abstraction for an HTTP web application, and it cannot perform the URL path or host-based routing that an ALB provides. Additionally, maintaining one instance per AZ across three AZs is over-provisioned and more costly than a two-AZ ALB architecture; an ALB with healthy targets in two AZs already meets typical high-availability requirements without the extra complexity and expense of an NLB.
- ✗
Migrate to a single larger instance in a different region
Why it's wrong here
Migrating to a single larger instance in a different region simply relocates the single point of failure rather than eliminating it, and it introduces significant cross-region network latency between users and the application. This approach also incurs higher data transfer costs and complexity around regional failover, without any benefit for the web application's immediate availability. It is not a valid high-availability strategy.
- ✓
Deploy EC2 instances across two Availability Zones and configure the ALB to distribute traffic
Why this is correct
Deploying EC2 instances across two Availability Zones behind an Application Load Balancer provides both fault isolation and active load balancing. The ALB performs health checks, routes traffic only to healthy instances, and can distribute requests across both AZs, so if one entire AZ becomes unavailable, the other continues to serve traffic. This is the standard architecture for achieving regional high availability with an HTTP web application.
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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 startup runs a web application on EC2 instances behind an Application Load Balancer. They want to improve resilience by distributing instances across multiple Availability Zones. Currently, all instances are in us-east-1a. They create a launch template and an Auto Scaling group with a desired capacity of 2. They configure the Auto Scaling group to use two subnets: one in us-east-1a and one in us-east-1b. However, after updating, all instances remain in us-east-1a. What is the most likely reason?
easy- ✓ A.The instance type is not available in us-east-1b.
- B.The Auto Scaling group's subnet configuration was not updated to include the new subnet.
- C.The new subnet in us-east-1b has no route to the internet.
- D.The launch template specifies a single subnet in us-east-1a.
Why A: The most likely reason is that the instance type is not available in us-east-1b. If the instance type is not supported in that Availability Zone, the Auto Scaling group cannot launch instances there, so it will launch all instances in the AZ where the instance type is available (us-east-1a). This is a common issue when using specialized instance types that are not available in all AZs.
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.