High Availability for Transport Layer Apps on EC2

SAA-C03 By islever Editorial Last updated

Determine high-performing and/or scalable network architectures. Design secure access to AWS resources.

Short answer

BD Configure a Network Load Balancer for TCP traffic and create an Auto Scaling group spanning multiple Availability Zones.

Question

A company hosts an application on Amazon EC2 instances that run in a single Availability Zone. The application is accessible by using the transport layer of the Open Systems Interconnection (OSI) model. The company needs the application architecture to have high availability. Which combination of steps will meet these requirements MOST cost-effectively? (Choose two.)
  1. Configure new EC2 instances in a different Availability Zone. Use Amazon Route 53 to route traffic to all instances.
  2. Configure a Network Load Balancer in front of the EC2 instances. Correct Answer
  3. Configure a Network Load Balancer for TCP traffic to the instances. Configure an Application Load Balancer for HTTP and HTTPS traffic to the instances.
  4. Create an Auto Scaling group for the EC2 instances. Configure the Auto Scaling group to use multiple Availability Zones. Configure the Auto Scaling group to run application health checks on the instances. Correct Answer
  5. Create an Amazon CloudWatch alarm. Configure the alarm to restart EC2 instances that transition to a stopped state.

Key Takeaways

The key insight is distinguishing between OSI layers: 'transport layer' implies TCP, requiring an NLB rather than an ALB, while HA requires multi-AZ distribution via Auto Scaling.

This question tests designing high availability for applications using the transport layer (TCP). The correct solution combines a Network Load Balancer with an Auto Scaling group across multiple Availability Zones.

Common mistake: Candidates often select Option C (NLB + ALB) assuming comprehensive coverage is needed, but the ALB is unnecessary and adds cost since the app only uses the transport layer, not the application layer (HTTP/HTTPS).

Expert Analysis

Why the Answer Is Correct

Option B provides the necessary load balancing capability for TCP traffic at the transport layer (Layer 4) without incurring the overhead of HTTP parsing. Option D ensures high availability by distributing instances across multiple Availability Zones and automatically replacing failed instances via health checks. Together, they provide a robust, cost-effective HA architecture.

Why the Other Options Are Wrong

Option A lacks load balancing, creating a single point of failure if one instance fails within a zone or if Route 53 DNS propagation delays occur during failover. Option C includes an Application Load Balancer (ALB), which operates at Layer 7; since the question specifies the transport layer, the ALB is redundant and violates the 'MOST cost-effectively' requirement. Option E relies solely on CloudWatch alarms to restart stopped instances, which does not address Availability Zone outages or provide load balancing.

Community Comment Notes

The community overwhelmingly agreed on BD, noting that 'transport layer means just NLB'. Many users highlighted that there was no mention of HTTP or application-layer features, making the ALB in Option C unnecessary. One user noted that 'C is more comprehensive', but this was countered by the cost-effectiveness constraint and the specific protocol layer mentioned.

Exam Strategy

Always map the protocol mentioned (e.g., TCP vs HTTP) to the correct load balancer type: NLB for Layer 4/TCP, ALB for Layer 7/HTTP. For High Availability questions, look for Multi-AZ deployment combined with either ELB or Auto Scaling as the primary indicators of resilience.

Frequently Asked Questions

Why is an Application Load Balancer (ALB) incorrect here?

The question specifies the application uses the transport layer (TCP), not the application layer (HTTP/HTTPS). An ALB is designed for Layer 7 routing and would be an unnecessary cost.

Can I use Route 53 instead of an NLB for this scenario?

Route 53 can distribute traffic across AZs, but it does not perform health checks at the application level or balance loads within an AZ as effectively as an ELB. It also has DNS propagation delays, making it less ideal for immediate HA compared to an NLB+ASG setup.

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Community Votes

BD
100%

100% of anonymous learners picked answer BD. Votes are pick records left by other test-takers — they are not the verified answer.

Discussion 9 contributions

Compiled from public community threads and reader submissions, lightly edited for clarity. Handles and vote tallies are shown as recorded, and comments reflect the views of individual contributors.

From public community threads 9

  1. Scheldon 👍 6
    AnswerBD There is no information about the ports numbers and only that means that we need to use NLB, ALB is only for HTTP hence there is no point of using that solution as connection can be done via any port for exampl 4000 Autoscaling with instances in multiple AZ is the best solution. it will allow run new EC2 if it fail and in case if whole AZ will go down we will have 2nd one.
  2. sandordini 👍 4
    No word about the HTTP/application layer, only OSI 4 - TCP > B, an NLB should be enough D: for Autoscaling.
  3. muhammadahmer36 👍 3
    as it mention "The application is accessible by using the transport layer" which is TCP, so no more information or reason to use ALB as well, so I will go for B+D
  4. Tanidanindo 👍 3
    transport layer means just NLB.
  5. xBUGx 👍 2
    question says the application is running on Transport Layer. i dont think there is need for ALB
Show 4 more comments
  1. mk168898 👍 2
    accessible by transport layer means not by application layer means no need ALB
  2. Awsbeginner87 👍 2
    B- since network layer operates at layer 4 i.e transport layer D- for hHA
  3. LuongTo 👍 2
    C is more comprehensive than B. I voted CD
  4. AbhiBK 👍 1
    Answer is A & D - By deploying EC2 instances in multiple Availability Zones (Option A), you ensure that your application remains available even if one Availability Zone experiences an outage. This setup provides redundancy and fault tolerance.

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