You are designing a new TCP-based service that must be highly available across Availability Zones and reachable via the publicly resolvable DNS name my.service.com. The service uses a fixed TCP port and requires fixed IP addresses that external partners will whitelist. Resources are deployed across multiple Availability Zones in a single Region. Which design meets these requirements?

The correct option meets all requirements. A Network Load Balancer (NLB) is ideal for TCP services requiring fixed IP addresses, as it can provision static Elastic IP addresses per Availability Zone. Registering EC2 instances with the NLB ensures high availability across zones. An A (alias) Route 53 record pointing to the NLB's DNS name provides the publicly resolvable DNS name. Sharing the NLB's Elastic IP addresses with partners satisfies the whitelisting requirement. The first incorrect option fails because registering EC2 instances directly with their EIPs in Route 53 bypasses the NLB's high-availability and health-checking features, and the NLB would not be used to expose the service. The second incorrect option is wrong because ECS task public IPs are dynamic, not fixed, and an NLB targets an entire cluster, not individual task IPs directly in an A record. The fourth incorrect option uses an Application Load Balancer (ALB), which is for HTTP/HTTPS, not raw TCP, and CNAME records don't directly associate public IPs with a domain for whitelisting fixed IPs.