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Difficulty: MediumHigh Availability and Disaster Recovery Design

A healthcare provider is designing a new telemedicine consultation platform. The platform runs on Amazon EC2 instances in private subnets across two Availability Zones in the us-east-1 (Primary) Region and needs a disaster recovery (DR) solution in the us-west-2 (Secondary) Region. The backend database is an Amazon RDS for PostgreSQL instance. The platform must meet a Recovery Time Objective (RTO) of 15 minutes and a Recovery Point Objective (RPO) of 5 minutes. To control costs, active application servers must not run in the recovery region during normal operations. Additionally, the platform must automatically route user traffic to the secondary region during a disaster, and outbound connectivity from the EC2 instances to external pharmacy APIs must be highly available and redundant within each region. Which architecture should a Solutions Architect design to meet these requirements?

  1. A
    Create an RDS PostgreSQL cross-region read replica in us-west-2. Deploy a single NAT Gateway in each region, routing all outbound traffic from both Availability Zones through this single NAT Gateway. Use a Route 53 Private Hosted Zone for internal database endpoint resolution and associate it with the VPCs in both regions. Configure a Route 53 Failover routing policy with health checks pointing to the primary Application Load Balancer. Keep the secondary Auto Scaling group at a desired capacity of 0, scaling it up and promoting the database replica during a failover.
  2. Create an RDS PostgreSQL cross-region read replica in us-west-2. Deploy a NAT Gateway in each Availability Zone in both regions. Use a Route 53 Private Hosted Zone for internal database endpoint resolution and associate it with the VPCs in both regions. Configure a Route 53 Failover routing policy with health checks pointing to the primary Application Load Balancer. Keep the secondary Auto Scaling group at a desired capacity of 0, scaling it up and promoting the database replica during a failover.Answer
  3. C
    Configure daily RDS snapshots and copy them to us-west-2. Deploy a NAT Gateway in each Availability Zone in both regions. Use a Route 53 Private Hosted Zone for internal database endpoint resolution and associate it with the VPCs in both regions. Configure Route 53 Latency routing to distribute traffic between the two regions, keeping the application servers active in both regions.
  4. D
    Create an RDS PostgreSQL cross-region read replica in us-west-2. Deploy a NAT Gateway in each Availability Zone in both regions. Use a Route 53 Private Hosted Zone for internal database endpoint resolution and associate it only with the primary VPC. Configure a Route 53 Failover routing policy with health checks pointing to the primary Application Load Balancer. Keep the secondary Auto Scaling group at a desired capacity of 0, scaling it up and promoting the database replica during a failover.

Answer

The correct architecture uses an Amazon RDS cross-region read replica, redundant NAT Gateways in each Availability Zone, a Route 53 Private Hosted Zone associated with both VPCs, a Route 53 Failover routing policy, and a secondary Auto Scaling group with a capacity of 0.
The correct architecture leverages an Amazon RDS cross-region read replica to meet the 5-minute RPO requirement via low-latency asynchronous replication. By keeping the secondary Auto Scaling group's desired capacity at 0, compute costs are minimized during normal operations. Deploying NAT Gateways in every Availability Zone within both regions prevents a single point of failure for outbound connections to external APIs. Associating the Route 53 Private Hosted Zone with both the primary and secondary VPCs ensures that the application servers in the recovery region can resolve the database endpoint upon failover. Finally, a Route 53 Failover routing policy dynamically redirects client traffic based on health check results.

Step-by-Step Solution

1
Evaluate the replication strategy for the Amazon RDS for PostgreSQL database to meet the 5-minute RPO constraint.
Determine that an RDS cross-region read replica is required, as snapshot-based backups are too infrequent.
Cross-region read replicas provide near-continuous asynchronous replication, keeping data lag well under 5 minutes.
2
Design the compute layer for the secondary region to satisfy the cost-minimization constraint while meeting the 15-minute RTO.
Configure an Auto Scaling group in the secondary region with a desired capacity of 0, to be scaled up to active instances only during failover.
This avoids ongoing EC2 costs in the secondary region, and scaling up takes only a few minutes, fitting within the 15-minute RTO.
3
Verify networking and DNS requirements for outbound connectivity and database resolution in the secondary region.
Deploy NAT Gateways in each Availability Zone of both regions, and associate the Route 53 Private Hosted Zone for the database endpoint with both the primary and secondary VPCs.
A single NAT Gateway per region is a single point of failure. The database Private Hosted Zone must be associated with the recovery VPC to allow the scaled-up EC2 instances to resolve the database's endpoint.

Key Concept

Multi-region disaster recovery design balancing RTO/RPO requirements, cost optimization, local NAT redundancy, and Route 53 DNS routing/private hosted zone associations.
Estimated Time:2m 0s
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Topics

High Availability and Disaster Recovery Design

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