CLF-C02 Cloud Technology and Services Practice Question
A company is running their application on EC2 instances behind an Application Load Balancer. They want to ensure the application remains available during an AZ outage. What is the minimum architecture configuration required?
⚠ Common exam trap
Many exam-takers confuse 'multiple subnets' with 'multiple Availability Zones,' assuming that deploying across subnets within the same AZ provides fault tolerance, but subnets are AZ-scoped and do not offer AZ-level redundancy.
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
✓
EC2 instances distributed across at least two Availability Zones behind an ALB
To remain available during an Availability Zone outage, the application must be resilient to the failure of an entire AZ. An Application Load Balancer distributes traffic across healthy targets, but it cannot route to instances in a failed AZ. Therefore, EC2 instances must be deployed in at least two separate Availability Zones, and the ALB must be configured with subnets in those same AZs to route traffic and perform health checks, ensuring continuous availability if one AZ goes down.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Multiple EC2 instances in a single Availability Zone
Why it's wrong here
Multiple instances in a single Availability Zone protect against the loss of any one individual instance, but they share the same underlying power, cooling, and networking infrastructure of that AZ. If the entire Availability Zone experiences an outage, all instances become unavailable at the same time, so this architecture cannot provide availability during an AZ-wide failure.
- ✓
EC2 instances distributed across at least two Availability Zones behind an ALB
Why this is correct
An Application Load Balancer is a regional service that distributes incoming traffic across targets in multiple Availability Zones. By placing EC2 instances in at least two different AZs and registering them with an ALB, the ALB continually monitors target health and automatically reroutes traffic away from an unhealthy or unreachable AZ. This design ensures that the application remains available even if one entire Availability Zone fails.
- ✗
A single large EC2 instance with enhanced networking
Why it's wrong here
A single large instance with enhanced networking such as the Elastic Network Adapter provides higher throughput and lower latency, but it is still one compute resource running in one specific Availability Zone. Any instance failure, hardware malfunction, or even a routine AWS maintenance event will bring the application down, making this a single point of failure. Enhanced networking improves network performance only; it offers no redundancy or resiliency against failures.
- ✗
EC2 instances in a single Region across multiple subnets in the same AZ
Why it's wrong here
Subnets are simply logical ranges of IP addresses carved out of a VPC within a single Availability Zone; they do not represent distinct physical locations or independent infrastructure. Multiple subnets within the same AZ all run on the same hardware, power grid, and network spine, so an outage in that AZ will affect every instance regardless of which subnet it is in. This setup gives no AZ-level fault tolerance, it only provides segmented network security groups or routing policies.
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This CLF-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 CLF-C02 exam.