Answer: Set up a VPC peering connection between VPC-A and VPC-B.

## Explanation **Correct Answer: A - Set up a VPC peering connection between VPC-A and VPC-B.** **Why this is correct:** 1. **VPC Peering** is specifically designed to connect two VPCs together, allowing resources in different VPCs to communicate with each other using private IP addresses. 2. **Cross-account support**: VPC peering can be established between VPCs in different AWS accounts, which meets the requirement that both VPCs are in separate AWS accounts. 3. **No single point of failure**: VPC peering connections are highly available and redundant by design. The traffic flows through the AWS backbone network, which is designed for high availability. 4. **No bandwidth concerns**: VPC peering connections do not have bandwidth limitations or throughput constraints like VPN connections might have. The traffic uses AWS's internal network infrastructure. 5. **Secure access**: Communication between peered VPCs stays within the AWS network and does not traverse the public internet, providing enhanced security. **Why other options are incorrect:** **B. Set up VPC gateway endpoints for the EC2 instance running in VPC-B.** - VPC gateway endpoints are for accessing AWS services (like S3, DynamoDB) from within a VPC, not for connecting to EC2 instances in another VPC. - Gateway endpoints don't facilitate VPC-to-VPC connectivity. **C. Attach a virtual private gateway to VPC-B and set up routing from VPC-A.** - Virtual private gateways are for VPN connections from on-premises networks to AWS VPCs, not for VPC-to-VPC connectivity. - This would require setting up a VPN connection which could have bandwidth limitations and potentially create a single point of failure. **D. Create a private virtual interface (VIF) for the EC2 instance running in VPC-B and add appropriate routes from VPC-A.** - Private virtual interfaces are for AWS Direct Connect connections, which are for connecting on-premises data centers to AWS. - This is not designed for VPC-to-VPC connectivity and would be unnecessarily complex and expensive for this use case. **Key AWS Concepts:** - **VPC Peering**: A networking connection between two VPCs that enables you to route traffic between them using private IPv4 or IPv6 addresses. - **Cross-account VPC peering**: Requires the owner of the requester VPC to send a peering request to the owner of the accepter VPC. - **Security considerations**: Security groups and network ACLs still apply to traffic between peered VPCs, allowing you to control access. - **Routing**: You must update route tables in both VPCs to route traffic destined for the peered VPC through the peering connection.