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Difficulty: Very hardEnhancing Reliability and Disaster Recovery

An enterprise operates a multi-account, multi-region architecture on AWS to support its core application. Account A (Production) hosts the primary application resources in the us-east-1 Region inside VPC-Prod, and the disaster recovery resources in the us-west-2 Region inside VPC-DR. The database layer is an Amazon Aurora PostgreSQL Global Database, with the primary cluster in us-east-1 and a secondary cluster in us-west-2.

Account B (Shared Services) hosts a Route 53 Private Hosted Zone (PHZ) named internal.production.local that contains critical service discovery records. The application in VPC-Prod relies on these records.

During a disaster recovery drill, the Solutions Architect identifies the following issues:
1. Microservices running in VPC-DR fail to resolve the service endpoints in internal.production.local during failover tests.
2. Outbound data replication and synchronization traffic from VPC-Prod to the secondary Region in us-west-2 is routed through a single NAT Gateway located in Availability Zone us-east-1a, posing a single point of failure.

The company requires a solution that minimizes replication failure risk, maintains a target recovery time objective (RTO) of 15 minutes, and resolves the cross-account DNS resolution issues.

Which TWO actions should the Solutions Architect take to address these requirements?

  1. In Account B, authorize the VPC association of the private hosted zone internal.production.local with VPC-DR in Account A using the Route 53 API. In Account A, associate VPC-DR with the private hosted zone.Answer
  2. In Account A, deploy a NAT Gateway in each Availability Zone of VPC-Prod, and configure the route tables of the private subnets in each Availability Zone to direct outbound replication traffic to the local NAT Gateway in that same Availability Zone.Answer
  3. C
    In Account B, configure a Route 53 Resolver outbound endpoint and a forwarding rule for the domain internal.production.local targeting the inbound endpoints of VPC-DR in Account A.
  4. D
    In Account A, configure the VPC route tables in VPC-Prod to route outbound traffic through a single NAT Gateway in us-east-1a, and configure a Route 53 health check that triggers an AWS Lambda function to update the route tables to point to a backup NAT Gateway in us-east-1b upon failure.
  5. E
    Configure AWS Backup to take continuous snapshots of the Aurora Global Database, and in the event of an outage, restore the database from the latest snapshot into VPC-DR using a Pilot Light recovery pattern.

Answer

Associate the private hosted zone cross-account and deploy redundant NAT Gateways in each Availability Zone.
To resolve the cross-account DNS resolution issue, the private hosted zone in Account B must be associated with the recovery VPC (VPC-DR) in Account A. In AWS Route 53, cross-account association requires the hosted zone owner (Account B) to authorize the association using the Route 53 API or AWS CLI. Once authorized, the VPC owner (Account A) must complete the association. To eliminate the single point of failure for outbound replication and synchronization traffic, a NAT Gateway should be deployed in each Availability Zone where resources reside. Routing traffic from private subnets to a local NAT Gateway in the same Availability Zone ensures high availability and resilience against an Availability Zone outage.

Step-by-Step Solution

1
Identify the mechanism for sharing the private hosted zone (PHZ) across accounts.
Recognize that Route 53 private hosted zones require cross-account association authorization from the owner account (Account B) and then acceptance/association from the consumer account (Account A).
This resolves the DNS resolution issue for resources in VPC-DR during disaster recovery without introducing the complexity of Route 53 Resolver endpoints.
2
Address the single point of failure in the outbound replication path.
Deploy a NAT Gateway in each Availability Zone of VPC-Prod and update the corresponding route tables.
This ensures that traffic from private subnets in different Availability Zones flows through local NAT Gateways, maintaining high availability and preventing an AZ outage from breaking replication.
3
Evaluate database disaster recovery options against RTO/RPO requirements.
Determine that promoting the secondary cluster of the Aurora Global Database is the proper path for low-latency failovers, while backup restoration methods are too slow for the 15-minute RTO.
Aligns the DR strategy with the existing Aurora Global Database architecture to meet recovery objectives.

Key Concept

Multi-Region reliability requires eliminating single points of failure in the network path (redundant NAT Gateways) and ensuring correct cross-account service discovery configuration (Route 53 Private Hosted Zone cross-account association) to meet low Recovery Time Objectives (RTO).
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Topics

Enhancing Reliability and Disaster Recovery