SAP-C02 Design for New Solutions Practice Question
A company is designing a new web application that will run on Amazon EC2 instances behind an Application Load Balancer. The application must be highly available across multiple Availability Zones. Which TWO actions should the architect take? (Choose TWO.)
⚠ Common exam trap
It's easy for candidates to think launching instances in a single AZ is sufficient if the ALB is configured across multiple AZs, but the ALB requires healthy targets in each enabled AZ to maintain high availability; without instances in at least two AZs, the ALB cannot route traffic if the sole AZ fails.
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
✓
Configure the ALB as internet-facing and attach it to multiple Availability Zones.
Option B is correct because an internet-facing Application Load Balancer must be attached to subnets in multiple Availability Zones so it can distribute incoming traffic across those zones and remain resilient if one AZ fails. Option C is correct because the EC2 instances themselves must be launched in at least two Availability Zones; an ALB can only route to targets in the AZs it is enabled for, so placing instances in multiple AZs is what actually makes the application highly available. Option A is wrong because confining all instances to a single AZ creates a single point of failure and defeats the multi-AZ requirement. Option D is wrong because the scenario specifies an Application Load Balancer for a web application, and swapping to an NLB is neither required nor appropriate for HTTP/HTTPS layer-7 routing. Option E is wrong because Elastic IP addresses are not needed for instances behind an ALB; the ALB's nodes handle public addressing, and EIPs do not provide multi-AZ high availability.
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 all EC2 instances in a single Availability Zone.
Why it's wrong here
Placing every instance in one Availability Zone means an AZ failure takes down all targets, so the load balancer has no healthy capacity elsewhere. It is tempting because single-AZ deployment reduces latency and data-transfer costs for non-production or fault-tolerant workloads.
- ✓
Configure the ALB as internet-facing and attach it to multiple Availability Zones.
Why this is correct
An internet-facing ALB distributes client traffic and, when attached to multiple Availability Zones, its nodes reside in each of those zones. This removes the load balancer as a single point of failure, satisfying the multi-AZ high availability requirement for the web tier.
- ✓
Launch EC2 instances in at least two Availability Zones.
Why this is correct
Spreading instances across two or more Availability Zones satisfies the multi-AZ high-availability constraint: each AZ has independent power, cooling and networking, so an AZ failure leaves capacity in the remaining zone. The Application Load Balancer then routes only to healthy targets in surviving zones, maintaining service.
- ✗
Use a Network Load Balancer instead of an Application Load Balancer.
Why it's wrong here
A Network Load Balancer operates at layer 4 and cannot perform the HTTP/HTTPS path-based or host-based routing the application requires; it also does not by itself span AZs for the instances. It is tempting because NLB suits extreme throughput or static IP requirements at TCP level.
- ✗
Assign Elastic IP addresses to each EC2 instance.
Why it's wrong here
Elastic IP addresses provide static public IPv4 addressing for a single instance, not cross-AZ redundancy; they cannot float between instances or AZs automatically. They suit whitelisting a fixed outbound address. High availability requires instances in multiple AZs behind the ALB, which already distributes traffic.
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