A developer is building an application on a fleet of Amazon EC2 Linux instances that...

The requirement in this scenario is encryption in transit for sensitive data exchanged between two EC2-based application fleets. AWS best practices clearly distinguish between network isolation and transport-layer encryption. Security groups (Option A) restrict traffic but do not encrypt it. EBS encryption (Option C) protects data at rest and does not affect data transmitted over the network.

Although a Site-to-Site VPN (Option B) would encrypt traffic, AWS documentation considers this approach unnecessary and operationally heavy when both workloads run inside AWS and application-level encryption is sufficient.

The most efficient and AWS-recommended approach is to use TLS (HTTPS) for application communication. AWS Certificate Manager (ACM) allows developers to provision and manage TLS certificates without manual certificate handling. Apache can be configured to use HTTPS with ACM-issued certificates, ensuring that all API traffic between the fleets is encrypted in transit using industry-standard TLS.

AWS documentation consistently recommends TLS for service-to-service communication within AWS when sensitive data is transmitted. This approach minimizes operational overhead, avoids additional networking infrastructure, and integrates natively with existing EC2-based applications.

Therefore, using ACM-issued certificates and HTTPS for Apache communication is the correct and most efficient solution.