ALB High Availability — Internet-Facing and Multi-AZ Instances
A company is designing a highly available architecture for a web application using an Application Load Balancer (ALB) across multiple Availability Zones. Which TWO actions should be taken to ensure high availability?
Quick Answer
The correct answer is to configure the ALB as internet-facing and place the EC2 instances in multiple Availability Zones. An internet-facing ALB is required because it receives traffic directly from users over the internet, routing it to healthy targets, while deploying instances across multiple AZs ensures the application survives an entire AZ failure without downtime. On the AWS Certified Advanced Networking Specialty ANS-C01 exam, this scenario tests your understanding of high availability design patterns for load balancers, often appearing as a trap where candidates confuse internal versus internet-facing ALBs or mistakenly propose a single-AZ deployment. A common memory tip is to remember that “internet-facing” equals public traffic ingress, and “multi-AZ” equals fault tolerance—if either is missing, the architecture is not highly available. For quick recall, think “ALB HA: public face + spread across space.”
⚠ Common exam trap
The ANS-C01 exam often tests the misconception that using a Network Load Balancer instead of an Application Load Balancer improves high availability, but the trap is that high availability depends on distributing targets across multiple AZs, not on the load balancer type, and the question explicitly requires an ALB for Layer 7 features.
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
✓
Register EC2 instances in multiple Availability Zones.
Registering EC2 instances in multiple Availability Zones ensures that if one AZ becomes unavailable, the ALB can route traffic to healthy instances in another AZ. This is a fundamental requirement for high availability because the ALB distributes incoming traffic across targets in different AZs, and if all instances are in a single AZ, that AZ becomes a single point of failure.
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 Network Load Balancer instead of an ALB.
Why it's wrong here
NLB is for TCP/UDP, not HTTP.
- ✓
Register EC2 instances in multiple Availability Zones.
Why this is correct
Multi-AZ provides fault tolerance.
- ✗
Place the EC2 instances in a single Availability Zone.
Why it's wrong here
Single AZ is not highly available.
- ✗
Configure the ALB as internal.
Why it's wrong here
Internal ALB is not accessible from internet.
- ✓
Configure the ALB as internet-facing.
Why this is correct
Internet-facing ALB receives user traffic.
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Same concept, more angles
1 more way this is tested on ANS-C01
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 company is designing a highly available architecture for a web application using an Application Load Balancer (ALB) in multiple Availability Zones. Which TWO configurations are required to achieve high availability?
medium- ✓ A.The ALB must be configured with subnets in at least two Availability Zones
- ✓ B.The ALB must be internet-facing
- C.At least three EC2 instances must be registered with the ALB
- D.A NAT gateway must be deployed in each Availability Zone
- E.Cross-zone load balancing must be enabled on the ALB
Why A: The ALB must be configured with subnets in at least two Availability Zones to remain available if one AZ fails. Option B is correct because an internet-facing ALB is required to accept traffic from the internet; an internal ALB would not be accessible. Option C is incorrect because high availability does not require three instances; two instances (one per AZ) can provide high availability. Option D is incorrect because NAT gateways are not required for ALB high availability; they are used for outbound internet access from private subnets. Option E is incorrect because cross-zone load balancing is enabled by default, but it is not a requirement for high availability; high availability is achieved by having instances in multiple AZs.
JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This ANS-C01 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 ANS-C01 exam.