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Difficulty: MediumHigh Availability and Disaster Recovery Design

A financial technology company is designing a new multi-region web application for electronic contract signatures. The application requires a Recovery Time Objective (RTO) of 15 minutes and a Recovery Point Objective (RPO) of 1 minute. The primary infrastructure is located in the eu-west-2 (London) region, and the disaster recovery (DR) region is eu-west-1 (Ireland). The application tier consists of Amazon EC2 instances in private subnets that must access the internet to download software updates and contact external identity validation APIs. The database layer uses Amazon Aurora PostgreSQL. A private DNS endpoint db.internal.contract.com is managed in a Route 53 Private Hosted Zone for database connection strings. Which configuration should a Solutions Architect recommend to meet these requirements with high availability?

  1. A
    Deploy an Aurora Global Database with the primary cluster in eu-west-2 and a secondary cluster in eu-west-1. Deploy the EC2 instances in Auto Scaling groups across multiple Availability Zones in both regions. Deploy a single NAT Gateway in one public subnet in eu-west-2 and a single NAT Gateway in eu-west-1 to route outbound traffic for all private subnets. Associate the Route 53 Private Hosted Zone with the VPCs in both regions. Configure Route 53 Failover routing for the public application endpoint.
  2. B
    Deploy an Aurora PostgreSQL cluster in eu-west-2 and schedule automated snapshots every 4 hours, copying them to eu-west-1. Deploy the EC2 instances in Auto Scaling groups in eu-west-2, and configure an AWS CloudFormation template to deploy the application stack in eu-west-1 during a disaster. Associate the Route 53 Private Hosted Zone with both VPCs. Configure Route 53 Failover routing for the public application endpoint.
  3. Deploy an Aurora Global Database with the primary cluster in eu-west-2 and a secondary cluster in eu-west-1. Deploy the EC2 instances in Auto Scaling groups across multiple Availability Zones in both regions, with redundant NAT Gateways in each Availability Zone where private subnets are deployed. Associate the Route 53 Private Hosted Zone with the VPCs in both eu-west-2 and eu-west-1. Configure Route 53 Failover routing for the public application endpoint pointing to the Application Load Balancers in both regions.Answer
  4. D
    Deploy an Aurora Global Database with the primary cluster in eu-west-2 and a secondary cluster in eu-west-1. Deploy the EC2 instances in Auto Scaling groups across multiple Availability Zones in both regions, with redundant NAT Gateways in each Availability Zone where private subnets are deployed. Associate the Route 53 Private Hosted Zone only with the VPC in eu-west-2. Configure Route 53 Failover routing for the public application endpoint pointing to the Application Load Balancers in both regions.

Answer

The correct configuration is to deploy an Aurora Global Database, associate the Private Hosted Zone with the VPCs in both regions, deploy redundant NAT Gateways in each Availability Zone, and configure Route 53 Failover routing.
Deploying an Aurora Global Database ensures that data is continuously replicated across regions to satisfy the 1-minute RPO, while providing fast regional failovers to satisfy the 15-minute RTO. Redundant NAT Gateways across multiple Availability Zones in each region ensure that outbound internet connections remain available even during a single Availability Zone outage. Associating the Private Hosted Zone containing the database DNS endpoints with both VPCs ensures that the application tier in both the active and standby regions can resolve the database connection hostname.

Step-by-Step Solution

1
Evaluate target RTO and RPO against replication methods.
An RPO of 1 minute and RTO of 15 minutes require continuous cross-region database replication. Amazon Aurora Global Database provides physical replication with typical lag under 1 second, meeting the RPO, and cluster promotion within a minute, meeting the RTO.
Backup-and-restore strategies utilizing snapshots cannot meet low RPO targets and require longer restore operations that exceed the RTO.
2
Evaluate NAT Gateway configurations for high availability.
NAT Gateways must be deployed in each Availability Zone containing private subnets that require outbound internet connectivity.
Deploying a single NAT Gateway in an Availability Zone creates a single point of failure. If that Availability Zone fails, instances in other zones lose outbound connectivity.
3
Configure DNS resolution for the private database endpoint across regions.
Associate the Route 53 Private Hosted Zone with the VPCs in both the primary (eu-west-2) and secondary (eu-west-1) regions.
Without this cross-VPC association, the EC2 instances in the secondary region will not be able to resolve the database's custom private domain name during a disaster recovery scenario.

Key Concept

Cross-region database replication, Private Hosted Zone VPC association, and Availability Zone redundant NAT Gateways for disaster recovery design.
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Topics

High Availability and Disaster Recovery Design

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