SAP-C02 Design for New Solutions Practice Question
A company is designing a new web application that will be deployed on Amazon EC2 instances behind an Application Load Balancer (ALB). The application must be highly available and fault-tolerant across multiple Availability Zones. Which THREE actions should the company take to meet these requirements? (Choose three.)
⚠ Common exam trap
Many exam-takers confuse vertical scaling (larger instances) with horizontal scaling and fault tolerance, or mistakenly think that using a single Availability Zone can be compensated by other means, ignoring the fundamental requirement for multi-AZ deployment.
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 an Auto Scaling group across multiple Availability Zones.
Option A is correct because an Auto Scaling group spanning multiple Availability Zones maintains capacity and automatically launches replacement instances when an AZ or instance fails, which is the foundation of high availability and fault tolerance. Option C is correct because ALB target group health checks continuously probe registered targets and, combined with the Auto Scaling group, cause unhealthy instances to be detected and replaced, restoring healthy capacity. Option D is correct because an Application Load Balancer is a regional, multi-AZ service that must have targets registered in multiple Availability Zones so it can route traffic away from a failed AZ and continue serving requests. Option B is not correct because a larger instance type only increases the capacity of a single instance and does nothing to provide redundancy across Availability Zones or to recover from failures. Option E is not correct because confining the deployment to a single Availability Zone creates a single point of failure and directly violates the multi-AZ high availability and fault tolerance requirement.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Launch EC2 instances in an Auto Scaling group across multiple Availability Zones.
Why this is correct
Launching EC2 instances in an Auto Scaling group across multiple Availability Zones satisfies the fault-tolerance requirement by distributing capacity so that an AZ failure does not take down the application. The Auto Scaling group also replaces unhealthy instances automatically, maintaining the desired capacity behind the ALB.
- ✗
Use a larger EC2 instance type to handle failures.
Why it's wrong here
A larger instance type increases capacity on one host but does not span Availability Zones, so an AZ outage still takes the application down. Vertical scaling suits performance or memory constraints, whereas fault tolerance requires instances distributed across multiple Availability Zones behind the ALB.
- ✓
Configure health checks on the ALB target group to automatically replace unhealthy instances.
Why this is correct
ALB health checks detect failed targets and trigger Auto Scaling replacement, restoring capacity without manual intervention. This satisfies the fault-tolerance requirement by ensuring unhealthy EC2 instances are removed from rotation and replaced, maintaining availability across the remaining Availability Zones.
- ✓
Configure the ALB to route traffic to instances in multiple Availability Zones.
Why this is correct
Distributing ALB nodes across multiple Availability Zones directly satisfies the fault-tolerance requirement: if one AZ fails, the load balancer continues routing to healthy targets in surviving zones. Cross-zone load balancing then spreads traffic evenly, keeping the application available during an AZ outage.
- ✗
Use a single Availability Zone to reduce latency.
Why it's wrong here
Concentrating instances in one Availability Zone means an AZ failure removes all capacity, defeating fault tolerance. Single-AZ deployment would be acceptable for development or latency-sensitive workloads tolerating outages, but high availability requires subnets and instances spread across at least two Availability Zones.
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Senior Network & Security Engineer · founder of Courseiva
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