Question

Difficulty: Very hardNetworking and Connectivity Design

An enterprise is designing a highly resilient hybrid network architecture to connect its AWS multi-Region environment with an on-premises datacenter. The AWS deployment spans two Regions: `us-east-1` (containing `vpc-app-use1` for workloads and `vpc-sec-use1` for egress security control) and `us-west-2` (containing `vpc-app-usw2` for workloads and `vpc-sec-usw2` for egress security control). A single 10 Gbps10\text{ Gbps} AWS Direct Connect connection terminates at a Direct Connect Gateway (`dxgw-global`). The solution must satisfy the following requirements:
1. VPCs within each Region must route inter-VPC traffic via a regional AWS Transit Gateway (`tgw-use1` and `tgw-usw2`).
2. Workloads in both Regions must access the on-premises network with minimal latency and high availability.
3. Outbound internet traffic from application VPCs must route through the security VPC in their respective Region. This traffic must remain highly available even during an Availability Zone (AZ) outage, without routing across Regions.
4. Active Directory DNS queries for `corp.local` must resolve to on-premises DNS servers, while queries for the Route 53 Private Hosted Zone (PHZ) `aws.corp` (hosted in a centralized AWS account) must resolve across all VPCs.

Which of the following connectivity and DNS configurations meets these requirements while minimizing latency and single points of failure?

  1. A
    Associate `dxgw-global` only with `tgw-use1` in the primary Region. Establish a Transit Gateway peering connection between `tgw-use1` and `tgw-usw2` to route all on-premises traffic from `us-west-2` transitively through the peering link. Deploy redundant NAT Gateways across multiple Availability Zones in `vpc-sec-use1` and `vpc-sec-usw2`. Point the default route (0.0.0.0/00.0.0.0/0) in the application VPCs to their local Transit Gateway, routing to the local security VPC. Associate the `aws.corp` Private Hosted Zone with all VPCs in both Regions.
  2. Associate `dxgw-global` with both `tgw-use1` and `tgw-usw2` using transit virtual interfaces. Establish a Transit Gateway peering connection between `tgw-use1` and `tgw-usw2` for inter-Region VPC-to-VPC traffic. Deploy redundant NAT Gateways across multiple Availability Zones in both `vpc-sec-use1` and `vpc-sec-usw2`. In the route tables of the application VPCs, point the default route (0.0.0.0/00.0.0.0/0) to the local Transit Gateway, which routes to the local security VPC. Create Route 53 Resolver outbound endpoints in the security VPCs of both Regions and configure forwarding rules for `corp.local` pointing to the on-premises DNS servers. Authorize cross-account Private Hosted Zone association and associate the `aws.corp` Private Hosted Zone with all application and security VPCs in both Regions.Answer
  3. C
    Associate `dxgw-global` with both `tgw-use1` and `tgw-usw2` using transit virtual interfaces. Establish a Transit Gateway peering connection between `tgw-use1` and `tgw-usw2`. Deploy a single NAT Gateway in a single Availability Zone in both `vpc-sec-use1` and `vpc-sec-usw2` to minimize NAT gateway costs. In the route tables of the application VPCs, point the default route (0.0.0.0/00.0.0.0/0) to the local Transit Gateway, which routes to the local security VPC. Create Route 53 Resolver outbound endpoints in the security VPCs of both Regions and configure forwarding rules for `corp.local` pointing to the on-premises DNS servers. Authorize cross-account Private Hosted Zone association and associate the `aws.corp` Private Hosted Zone with all application and security VPCs in both Regions.
  4. D
    Associate `dxgw-global` with both `tgw-use1` and `tgw-usw2` using transit virtual interfaces. Establish a Transit Gateway peering connection between `tgw-use1` and `tgw-usw2`. Deploy redundant NAT Gateways across multiple Availability Zones in both `vpc-sec-use1` and `vpc-sec-usw2`. In the route tables of the application VPCs, point the default route (0.0.0.0/00.0.0.0/0) to the local Transit Gateway, which routes to the local security VPC. Create Route 53 Resolver outbound endpoints in the security VPCs of both Regions and configure forwarding rules for `corp.local` pointing to the on-premises DNS servers. Associate the `aws.corp` Private Hosted Zone only with the centralized network account's VPC, and configure a Route 53 Resolver conditional forwarding rule in all application VPCs to forward queries for `aws.corp` to Route 53 Resolver inbound endpoints deployed in the network account's VPC.

Answer

The correct architecture associates the Direct Connect Gateway with both Transit Gateways, deploys redundant NAT Gateways across multiple Availability Zones in both security VPCs, configures Route 53 Resolver outbound endpoints for on-premises DNS resolution, and authorizes cross-account Private Hosted Zone association for the application and security VPCs.
The correct configuration establishes direct association between the Direct Connect Gateway and the Transit Gateways in both Regions, ensuring low-latency and compliant transit routing to the on-premises network. It ensures high availability for egress traffic by deploying redundant NAT Gateways across multiple Availability Zones in both security VPCs. For DNS resolution, it correctly configures Route 53 Resolver outbound endpoints for on-premises forwarding and utilizes cross-account PHZ association to resolve the `aws.corp` zone in all VPCs.

Step-by-Step Solution

1
Evaluate hybrid connectivity and transit capabilities over AWS Direct Connect.
AWS Transit Gateway peering does not support transitive routing for traffic from a Direct Connect Gateway or VPN attachment. Peering Transit Gateways to route on-premises traffic from a remote Region will fail.
This establishes that the Direct Connect Gateway must be directly associated with both `tgw-use1` and `tgw-usw2` using transit virtual interfaces.
2
Analyze outbound internet routing and high availability constraints.
Deploying a single NAT Gateway in a security VPC creates a single point of failure. Redundant NAT Gateways must be placed across multiple Availability Zones in both `vpc-sec-use1` and `vpc-sec-usw2` to ensure high availability during an Availability Zone outage.
This rules out configurations that compromise egress redundancy to save costs.
3
Determine Private Hosted Zone (PHZ) resolution requirements across multiple accounts and VPCs.
Using Route 53 Resolver forwarding rules to point to inbound endpoints to resolve a Private Hosted Zone is unsupported. The PHZ must be explicitly associated with each VPC in all accounts that require name resolution.
This validates that cross-account PHZ association is mandatory for the application and security VPCs to resolve the `aws.corp` domain.
4
Configure on-premises domain resolution.
Create Route 53 Resolver outbound endpoints in the security VPCs of both Regions and associate conditional forwarding rules for `corp.local` pointing to the on-premises DNS servers.
This ensures that DNS queries for the on-premises directory resolve correctly through the Direct Connect path.

Key Concept

Multi-Region hybrid networking, Transit Gateway routing limitations, and Private Hosted Zone cross-VPC association.
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