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Difficulty: HardHigh Availability and Disaster Recovery Design

An energy trading company is designing a disaster recovery (DR) architecture for its core trade execution platform on AWS. The primary workload runs in the us-east-1 Region, and the secondary DR site is in the us-west-2 Region. The business requires a Recovery Time Objective (RTO) of less than 15 minutes and a Recovery Point Objective (RPO) of less than 1 minute. The architecture must satisfy the following:
- Within each region, the infrastructure must be highly available across multiple Availability Zones.
- The application tier runs on Amazon EC2 instances in private subnets behind an Application Load Balancer (ALB).
- Private microservices within the VPC communicate using a Route 53 private hosted zone named trading.internal.
- The application requires outbound internet connectivity to communicate with external clearinghouses.
- The database backend is Amazon Aurora PostgreSQL.

Which design meets the business requirements while minimizing cost and operational complexity?

  1. A
    Configure an Amazon Aurora Global Database with the primary cluster in us-east-1 and a secondary cluster in us-west-2 containing a single db.r6g.large instance. Associate the trading.internal private hosted zone with the VPCs in both us-east-1 and us-west-2. Deploy a single NAT Gateway in one Availability Zone in each region's VPC. Configure an Amazon Route 53 failover routing policy with health checks associated with the ALBs to route client traffic.
  2. B
    Configure an Amazon Aurora Global Database with the primary cluster in us-east-1 and a secondary cluster in us-west-2 containing a single db.r6g.large instance. Create the trading.internal private hosted zone in the us-east-1 VPC but do not associate it with the us-west-2 VPC. Deploy NAT Gateways in each Availability Zone within both regions' VPCs. Configure an Amazon Route 53 failover routing policy with health checks associated with the ALBs to route client traffic.
  3. Configure an Amazon Aurora Global Database with the primary cluster in us-east-1 and a secondary cluster in us-west-2 containing a single db.r6g.large instance. Associate the trading.internal private hosted zone with the VPCs in both us-east-1 and us-west-2. Deploy NAT Gateways in each Availability Zone within both regions' VPCs. Configure an Amazon Route 53 failover routing policy with health checks associated with the ALBs to route client traffic.Answer
  4. D
    Configure hourly Amazon Aurora database snapshot exports in us-east-1 and copy them to us-west-2 using AWS Backup. Associate the trading.internal private hosted zone with the VPCs in both us-east-1 and us-west-2. Deploy NAT Gateways in each Availability Zone within both regions' VPCs. Configure an Amazon Route 53 latency-based routing policy to route client traffic to the lowest-latency region.

Answer

Configure an Amazon Aurora Global Database with a single instance in the secondary region, associate the private hosted zone with both VPCs, deploy NAT Gateways in each Availability Zone, and use Route 53 failover routing.
The correct design uses Amazon Aurora Global Database to achieve replication times of less than 1 second, meeting the RPO of less than 1 minute. It allows promotion of the secondary cluster in minutes, meeting the RTO of less than 15 minutes. To keep cost low, the secondary region has a single database instance (pilot light/warm standby footprint). Outbound traffic is kept highly available within each region by placing a NAT Gateway in each Availability Zone. Finally, internal DNS resolution functions correctly after failover because the private hosted zone is associated with both the primary and secondary VPCs.

Step-by-Step Solution

1
Analyze database replication and disaster recovery limits.
Amazon Aurora Global Database provides storage-level, physical replication across regions with typical lag of less than one second, satisfying the RPO requirement of less than 1 minute. The secondary cluster can be promoted to write mode within minutes, satisfying the RTO requirement of less than 15 minutes.
Choosing the correct replication technology is critical to meet tight RTO and RPO requirements.
2
Determine private DNS requirements for multi-region failover.
A Route 53 Private Hosted Zone is only resolvable within VPCs that are explicitly associated with it. Therefore, the trading.internal zone must be associated with both the us-east-1 and us-west-2 VPCs.
Without this association, microservices in the secondary region will face DNS resolution failures during a disaster recovery event.
3
Evaluate intra-region high availability requirements for outbound traffic.
Deploying a NAT Gateway in each Availability Zone ensures that an outage in a single Availability Zone does not impact outbound traffic from instances in other zones.
A single NAT Gateway per VPC creates a single point of failure, violating the multi-AZ high availability requirement.
4
Establish external traffic routing and failover mechanics.
Configure a Route 53 failover routing policy referencing health checks on the regional Application Load Balancers.
This setup automates client redirection when the primary region becomes completely unreachable.

Key Concept

Multi-region disaster recovery pattern design matching RTO and RPO objectives, database replication, and network dependencies.
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Topics

High Availability and Disaster Recovery Design

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