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Difficulty: MediumHigh Availability and Disaster Recovery Design

A metropolitan public transit agency is designing a contactless fare validation system on AWS. The application tier runs on Amazon EC2 instances in private subnets across multiple Availability Zones in both the us-east-1 and us-west-2 Regions. The application must connect securely to external fare settlement endpoints on the public internet. Internal microservices rely on private DNS resolution for service discovery across all VPCs. Validation requests from devices must be routed to the closest Region with active failover capabilities to ensure high availability and low latency. The architecture must achieve a Recovery Time Objective (RTO) of less than 5 minutes and a Recovery Point Objective (RPO) of less than 1 minute.

Which two of the following configuration options should the Solutions Architect implement to meet these requirements? (Select TWO.)

  1. Deploy NAT Gateways in each Availability Zone of the VPCs in both Regions, updating the private subnet route tables to route outbound internet traffic to the local NAT Gateway in the same Availability Zone.Answer
  2. Configure Route 53 Latency routing records with active health checks to route public validation traffic to the Application Load Balancers in both Regions, automatically routing traffic away from a degraded Region.Answer
  3. C
    Deploy a single NAT Gateway in the primary Availability Zone of each Region's VPC, routing all outbound internet traffic from all private subnets through it to minimize NAT Gateway costs.
  4. D
    Create a Route 53 Private Hosted Zone in the us-east-1 VPC, and configure inter-region VPC peering to allow the us-west-2 VPC to automatically resolve internal DNS queries without local hosted zone association.
  5. E
    Configure Route 53 Geolocation routing records without health checks, relying on client-side retry logic to handle failover during regional outages.
  6. F
    Configure the database layer in us-east-1 and copy daily automated database snapshots to us-west-2 to restore the database cluster in the event of a regional disaster.

Answer

Deploy NAT Gateways in each Availability Zone of the VPCs in both Regions to ensure redundant outbound internet connectivity, and configure Route 53 Latency routing records with active health checks to route public validation traffic with low latency and automatic failover.
Deploying NAT Gateways in each Availability Zone provides fault tolerance for outbound traffic, ensuring that the loss of one Availability Zone does not impact outbound traffic from the other zones. Additionally, configuring Route 53 Latency routing with active health checks allows the agency to route validation traffic to the closest Region to minimize latency, while providing automatic failover within the 5-minute RTO boundary by detecting regional degradation and redirecting traffic to the remaining healthy Region.

Step-by-Step Solution

1
Evaluate the outbound connectivity requirements for high availability across Availability Zones.
Identified that deploying a NAT Gateway in each Availability Zone prevents an AZ outage from blocking outbound traffic in other zones.
Outbound connectivity to external fare settlement partners must remain highly available, requiring redundant NAT Gateways per AZ.
2
Evaluate the routing requirements for global validation requests.
Selected Route 53 Latency-based routing to ensure requests are routed to the closest Region to minimize validation latency.
The system requires low-latency routing to the closest Region while maintaining active failover capability.
3
Configure health checks on the Route 53 records.
Ensured that Route 53 can detect a regional outage and automatically fail over to the other Region within the 5-minute RTO.
Without health checks associated with the routing records, Route 53 cannot perform automatic DNS-level failover during an outage.

Key Concept

Designing multi-region disaster recovery and high availability with low-latency routing, redundant outbound gateways, and automated failover.
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Topics

High Availability and Disaster Recovery Design

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