Which solution will provide the required access MOST securely?
Create a DB instance security group that allows all traffic from the public IP address of the application server in VPC A.
Configure a VPC peering connection between VPC A and VPC B.
Make the DB instance publicly accessible. Assign a public IP address to the DB instance.
Launch an EC2 instance with an Elastic IP address into VPC B. Proxy all requests through the new EC2 instance.
Explanations:
Allowing all traffic from the public IP address of the application server exposes the database to potential attacks from any IP address that can spoof the public IP, making it less secure.
A VPC peering connection allows for secure, private communication between the two VPCs without exposing the database to the public internet. It provides a direct network path and maintains the security of both VPCs.
Making the DB instance publicly accessible increases its exposure to the internet, which poses significant security risks, including potential attacks and unauthorized access.
While this option could provide access, it introduces unnecessary complexity and potential performance bottlenecks by routing traffic through an additional EC2 instance. It also still requires proper security measures to protect the new EC2 instance.
I categorize that the answer is:
Configure a VPC peering connection between VPC A and VPC B.