Question

Difficulty: Very hardNetworking and Connectivity Design

An enterprise is designing a highly available, multi-account network architecture in the `us-east-1` Region. The architecture consists of one Shared Services VPC in Account A and three spoke application VPCs in Account B. An AWS Transit Gateway in Account A is used to interconnect all VPCs. The spoke VPCs require private DNS resolution of the `corp.internal` domain, which is managed in a Route 53 Private Hosted Zone in Account A. Additionally, all spoke VPCs must route outbound internet traffic through a centralized set of NAT Gateways in the Shared Services VPC. Spoke-to-spoke network communication must be blocked, but spoke-to-shared communication must be allowed. The design must be resilient to Availability Zone outages and minimize operational overhead.

Which TWO steps should the solutions architect take to meet these requirements? (Select TWO.)

  1. A
    Configure the spoke VPCs to route all DNS traffic on port 5353 directly to the Transit Gateway IP address, which will automatically forward the queries to the Shared Services VPC without any Route 53 Private Hosted Zone association or Route 53 Resolver endpoints.
  2. In the Shared Services VPC, deploy a NAT Gateway in a public subnet in each Availability Zone. In the private subnets hosting the Transit Gateway attachments, create Availability Zone-specific route tables that route 0.0.0.0/00.0.0.0/0 traffic to the NAT Gateway located in the corresponding Availability Zone.Answer
  3. C
    To minimize costs, deploy a single NAT Gateway in a public subnet of one Availability Zone in the Shared Services VPC, and configure all private subnet route tables across all Availability Zones to route outbound traffic to this single NAT Gateway.
  4. In Account A, authorize the association of the spoke VPCs with the `corp.internal` Private Hosted Zone. In Account B, associate each spoke VPC with the `corp.internal` Private Hosted Zone using the AWS CLI or Route 53 API.Answer
  5. E
    Associate all spoke VPCs and the Shared Services VPC with a single Transit Gateway route table, and attach an AWS network security group directly to the Transit Gateway resource to block spoke-to-spoke traffic while permitting spoke-to-shared traffic.

Answer

Deploy a NAT Gateway in each Availability Zone in the Shared Services VPC with AZ-specific routing, and perform a cross-account association of the spoke VPCs to the Private Hosted Zone using Route 53 association authorizations.
Deploying a NAT Gateway in each Availability Zone with AZ-specific routing in the Shared Services VPC prevents a single zone outage from causing a total egress failure. Authorizing and accepting cross-account Private Hosted Zone associations allows spoke VPCs in Account B to query the shared hosted zone in Account A directly and securely without the cost and latency of Resolver endpoints.

Step-by-Step Solution

1
Configure cross-account Route 53 Private Hosted Zone association by running the AWS CLI command to authorize association from the owner account (Account A) to the spoke VPCs (Account B).
The spoke VPCs are authorized to associate with the hosted zone.
Allows Account B to link its spoke VPCs to Account A's hosted zone.
2
Associate each spoke VPC in Account B with the Private Hosted Zone using the associate-vpc-with-hosted-zone command in Account B.
The spoke VPCs can now resolve the corp.internal domain privately.
Enables local Route 53 DNS resolvers in the spoke VPCs to query the shared zone.
3
Deploy one NAT Gateway per Availability Zone in the public subnets of the Shared Services VPC.
Multi-AZ redundant NAT Gateways are created.
Prevents a single AZ failure from disrupting outbound internet access for all VPCs.
4
Configure separate route tables for each Transit Gateway attachment subnet in the Shared Services VPC, routing default traffic (0.0.0.0/0) to the local NAT Gateway in the same Availability Zone.
Outbound internet traffic is routed redundantly with AZ affinity.
Maintains Availability Zone isolation and prevents cross-AZ dependency.

Key Concept

Cross-account DNS association and multi-AZ NAT Gateway routing redundancy in Transit Gateway architectures
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