Explanation

Correct Answer: A

Why Network Load Balancer (NLB) is the right choice:

1. TCP Protocol Support: NLB operates at Layer 4 (transport layer) and is specifically designed to handle TCP, UDP, and TLS traffic. This makes it ideal for TCP-based applications.

2. High Performance Requirements: The question states the application needs to handle 3 million requests per second with low latency. NLB is designed for extreme performance:

   • Can handle millions of requests per second
   • Provides ultra-low latencies
   • Uses a single static IP address per Availability Zone
   • Preserves source IP addresses

3. Non-Standard TCP Port: NLB can be configured to listen on any TCP port, including non-standard ports, which matches the requirement.

4. Public Accessibility: NLB can be deployed as an internet-facing load balancer, making it publicly accessible.

Why other options are incorrect:

B. Application Load Balancer (ALB):

• ALB operates at Layer 7 (application layer) and is optimized for HTTP/HTTPS traffic
• While ALB can technically handle TCP traffic, it's not optimized for high-performance TCP workloads
• ALB has lower performance ceilings compared to NLB for TCP traffic

C. Amazon CloudFront with ALB origin:

• CloudFront is a CDN service optimized for HTTP/HTTPS content delivery
• It doesn't support arbitrary TCP ports
• CloudFront is not designed for TCP-based applications
• The combination adds unnecessary complexity for a TCP workload

D. API Gateway with Lambda:

• API Gateway is designed for REST APIs and WebSocket connections
• It doesn't support arbitrary TCP ports
• Lambda with provisioned concurrency is for serverless HTTP workloads, not TCP applications
• This architecture would require significant re-architecture of the TCP application

Key AWS Service Characteristics:

• NLB: Layer 4, TCP/UDP/TLS, high performance, static IPs, preserves source IP
• ALB: Layer 7, HTTP/HTTPS, content-based routing, WebSocket support
• CloudFront: Global CDN, HTTP/HTTPS, edge locations, caching
• API Gateway: REST/WebSocket APIs, HTTP endpoints, serverless integration

For migrating a high-performance TCP application with specific port requirements, NLB provides the most direct and performant solution.