Refer to the following figure below
A user wishing to access an application installed in “EC2-B” instance in “VPC B” can be reached by. (Choose the best answer)

Answer options:

A.Using an Internet Gateway that can be attached to VPC B
B.Through EC2-A Public subnet & EC2-A Private subnet using a VPC Peeringconnection to EC2-B
C.Through EC2-A Public subnet & EC2-A Private subnet using a VPN connection to EC2-B
D.Instancesusing Private IP address cannot be connected using VPC Peering

Correct Answer: B
Instances within a VPC’s subnets can communicate with each other by default. In order to seamlessly connect between different networks, a concept called VPC Peering is introduced by AWS. Using a VPC Peering connection, instances in private subnets in two different networks can talk to each other. In the above diagram, since VPC B does not have an Internet Gateway, the only way that an User can reach the EC2-B instance is through a VPC peering connection between EC2-A & EC2-B
Option A is incorrect since this will involve modifications to the existing Architecture and dilute existing security configurations
Option B is CORRECT. The user can connect to VPC A, EC2-A Public, EC2-A Private, EC2-B Private to access applications installed on EC2-B
Option C is incorrect since a VPN connection is normally used to connect On premises Servers to AWS services using the Internet
Option D is incorrect since the only way to connect instances using Private IP’s in different networks is through VPC Peering
References:
https://youtu.be/HMInA8yMw1k
https://docs.aws.amazon.com/vpc/latest/peering/what-is-vpc-peering.html