Question

Difficulty: HardHybrid and Multi-Account Network Connectivity Design

An enterprise is designing a highly available, multi-account hybrid network architecture. The architecture consists of a Shared Services AWS account and 5050 spoke VPCs deployed across 33 Availability Zones (AZs) in the us-east-1 Region. The Shared Services account hosts a central Route 53 Private Hosted Zone (PHZ) for internal service discovery. The enterprise requires secure, transitive routing between the spoke VPCs and its on-premises data center, which will be connected via a 10 Gbps10\text{ Gbps} AWS Direct Connect connection with a backup AWS Site-to-Site VPN. Additionally, all outbound internet traffic from the spoke VPCs must be routed through a centralized egress VPC in the Shared Services account for security inspection. The solution must ensure high availability across all AZs, support internal DNS resolution, and prevent single points of failure. Which of the following designs meets these requirements?

  1. A
    Deploy a Direct Connect Gateway (DXGW) and associate it directly with the 5050 spoke VPCs using private virtual interfaces (private VIFs) to handle spoke-to-spoke and hybrid traffic routing, bypassing the need for AWS Transit Gateway. In the egress VPC, deploy redundant NAT Gateways across all 33 Availability Zones. Associate the Route 53 Private Hosted Zone in the Shared Services account with all 5050 spoke VPCs. Set up a backup Site-to-Site VPN connection to each individual spoke VPC.
  2. B
    Deploy an AWS Transit Gateway in the Shared Services account and share it with the spoke VPC accounts using AWS Resource Access Manager (RAM). Attach the spoke VPCs and the centralized egress VPC to the Transit Gateway. In the egress VPC, deploy redundant NAT Gateways across all 33 Availability Zones. Attach the Direct Connect connection via a transit virtual interface (transit VIF) to a Direct Connect Gateway (DXGW) associated with the Transit Gateway, and establish a backup Site-to-Site VPN connection. Create the Route 53 Private Hosted Zone in the Shared Services account and associate it only with the egress VPC, relying on Transit Gateway route propagation to transitively resolve internal DNS queries from the spoke VPCs.
  3. Deploy an AWS Transit Gateway in the Shared Services account and share it with the spoke VPC accounts using AWS Resource Access Manager (RAM). Attach the spoke VPCs and the centralized egress VPC to the Transit Gateway. In the egress VPC, deploy redundant NAT Gateways across all 33 Availability Zones and route internet-bound traffic through them. Associate the Route 53 Private Hosted Zone in the Shared Services account with all 5050 spoke VPCs. Attach the Direct Connect connection via a transit virtual interface (transit VIF) to a Direct Connect Gateway (DXGW) associated with the Transit Gateway, and establish a backup Site-to-Site VPN connection attached directly to the Transit Gateway.Answer
  4. D
    Deploy an AWS Transit Gateway in the Shared Services account and share it with the spoke VPC accounts using AWS Resource Access Manager (RAM). Attach the spoke VPCs and the centralized egress VPC to the Transit Gateway. In the egress VPC, deploy a single NAT Gateway in one Availability Zone to minimize running costs. Associate the Route 53 Private Hosted Zone in the Shared Services account with all 5050 spoke VPCs. Attach the Direct Connect connection via a transit virtual interface (transit VIF) to a Direct Connect Gateway (DXGW) associated with the Transit Gateway, and establish a backup Site-to-Site VPN connection attached directly to the Transit Gateway.

Answer

The configuration utilizing AWS Transit Gateway shared via RAM, redundant NAT Gateways across all Availability Zones in the egress VPC, Route 53 Private Hosted Zone associated with all 5050 spoke VPCs, and a Direct Connect Gateway using a transit VIF with a backup VPN attached directly to the Transit Gateway.
AWS Transit Gateway acts as a central hub to connect multiple VPCs and on-premises networks, enabling transitive routing. By sharing it via AWS Resource Access Manager (RAM), all spoke VPCs can attach to it. Redundant NAT Gateways across all 33 Availability Zones in the egress VPC guarantee high availability. Explicitly associating the Route 53 Private Hosted Zone with all 5050 spoke VPCs ensures they can resolve DNS queries. Connecting the Direct Connect via a transit VIF to a DXGW associated with the Transit Gateway, alongside a backup Site-to-Site VPN, provides a highly available hybrid network with automatic failover.

Step-by-Step Solution

1
Determine the transitive routing model for the 5050 spoke VPCs and the hybrid connection.
Select AWS Transit Gateway shared via AWS Resource Access Manager (RAM) to allow multi-account spoke VPCs to communicate with each other and the on-premises environment.
AWS Transit Gateway acts as a cloud router, supporting transitive spoke-to-spoke and hybrid routing, which is not supported by Direct Connect Gateway alone.
2
Design the centralized egress path for outbound internet traffic.
Route outbound traffic from the spoke VPCs through the Transit Gateway to a centralized egress VPC containing redundant NAT Gateways deployed across all 33 Availability Zones.
Redundant NAT Gateways across Availability Zones prevent a single Availability Zone outage from disrupting outbound internet access for the entire network.
3
Configure DNS resolution for the Private Hosted Zone (PHZ) in the multi-account architecture.
Explicitly associate the Route 53 PHZ in the Shared Services account with all 5050 spoke VPCs.
Transit Gateway does not route DNS resolution queries transitively; each VPC must be associated with the PHZ to resolve its DNS records.
4
Establish high-availability hybrid connectivity with failover.
Attach the Direct Connect connection via a transit virtual interface (transit VIF) to a DXGW associated with the Transit Gateway, and establish a backup Site-to-Site VPN connection directly to the Transit Gateway.
Transit VIF is required to connect Direct Connect to a Transit Gateway, and the VPN provides a cost-effective, high-availability backup path.

Key Concept

Hybrid and Multi-Account Network Connectivity Design
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