Fully Redundant & Managed Internet Access Solution for Application Servers

Correct Answer - B.

NAT Gateway is AWS Managed solution for internet to private subnets.

This NAT Gateway is deployed in the public subnet.

NAT Gateway is redundant in a specific AZ on which it is deployed.

For Multi-AZ redundancy, NAT Gateway needs to be deployed in each AZ with a default route from the private subnet.

Options A & D are incorrect as the client is looking for a fully managed solution.

NAT instance needs to be managed by the client.

Option C is incorrect as NAT Gateway is redundant in an AZ.

For multi-AZ redundancy, add a NAT Gateway in each AZ.

For more information on the use case for NAT instance & NAT Gateway, refer to the following URL.

https://docs.aws.amazon.com/vpc/latest/userguide/vpc-nat-comparison.html

To allow the application servers in the private subnets of multiple VPCs to access the Internet for downloading data from database servers deployed in the us-east-1 region, a NAT (Network Address Translation) solution needs to be implemented. This NAT solution will enable the private subnet resources to connect to the internet without being directly exposed to it. Additionally, the solution needs to be fully redundant and managed by AWS, as the client lacks the competency to manage it.

Option A: Create a NAT Instance in the Public subnet of any one AZ in the region. Add a default route in the private subnet pointing to NAT Instance.

This option involves setting up a NAT Instance in a public subnet of an Availability Zone (AZ) in the region. The private subnet resources will be configured to use the NAT Instance as their default gateway to access the internet. However, this solution is not fully redundant, as the failure of the NAT Instance or the AZ in which it is located will result in a loss of internet access for the private subnet resources.

Option B: Create a NAT Gateway in the Public subnet of each AZ in the region. Add a default route in the private subnet pointing to NAT Gateway.

This option involves setting up a NAT Gateway in each public subnet of the AZs in the region. The private subnet resources will be configured to use the NAT Gateway as their default gateway to access the internet. This solution is fully redundant, as the failure of a single NAT Gateway or AZ will not result in a loss of internet access for the private subnet resources. However, setting up multiple NAT Gateways in each AZ can increase costs.

Option C: Create a NAT Gateway in the Public subnet of any one AZ in the region. Add a default route in the private subnet pointing to NAT Gateway.

This option involves setting up a single NAT Gateway in the public subnet of any one AZ in the region. The private subnet resources will be configured to use the NAT Gateway as their default gateway to access the internet. This solution is also fully redundant, as the failure of the NAT Gateway or AZ in which it is located will not result in a loss of internet access for the private subnet resources. This solution is more cost-effective than Option B.

Option D: Create a NAT Instance in the Public subnet of each AZ in the region. Add a default route in the private subnet pointing to NAT Instance.

This option involves setting up a NAT Instance in the public subnet of each AZ in the region. The private subnet resources will be configured to use the NAT Instance in their respective AZs as their default gateway to access the internet. This solution is fully redundant but can be costly to implement and manage.

Therefore, Option C is the most suitable solution as it provides a fully redundant and cost-effective NAT Gateway in a single AZ in the region.