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Difficulty: MediumEnhancing Reliability and Disaster Recovery

An enterprise operates a critical order-processing application in the us-east-1 Region. The application layer runs on Amazon EC2 instances distributed across three Availability Zones (AZs) in private subnets. Outbound API validation requests are routed through a single NAT Gateway located in the us-east-1a public subnet. The database layer uses an Amazon Aurora PostgreSQL Global Database with the primary cluster in us-east-1 and a secondary cluster in us-west-2. A Route 53 Private Hosted Zone (PHZ) is used for internal microservice resolution. The company requires a disaster recovery strategy with a Recovery Time Objective (RTO) of 15 minutes and a Recovery Point Objective (RPO) of 1 minute. During a recent outage in us-east-1a, outbound API validation failed for the entire application, and DNS failover did not execute correctly. Which set of actions should the Solutions Architect recommend to meet the reliability and disaster recovery requirements?

  1. Deploy a NAT Gateway in each Availability Zone in us-east-1 and update the private subnet route tables. Implement an active-passive multi-region strategy by deploying warm standby EC2 instances in us-west-2, and associate the Route 53 Private Hosted Zone with the VPC in us-west-2. Use Route 53 Application Recovery Controller (ARC) routing controls and application-level health checks to orchestrate failover, promoting the Aurora secondary cluster to primary.Answer
  2. B
    Maintain the single NAT Gateway in us-east-1a to minimize baseline infrastructure costs. Implement a pilot light disaster recovery strategy in us-west-2 by keeping secondary EC2 instances shut down. Configure Route 53 active-passive failover records based on basic EC2 instance status checks, and rely on Aurora's automatic multi-region database failover to promote the secondary cluster.
  3. C
    Provision a NAT Gateway in each Availability Zone in us-east-1 and update the private subnet route tables. Set up warm standby EC2 instances in us-west-2. Configure Route 53 active-passive failover with health checks pointed directly to the individual EC2 instances, but do not associate the Route 53 Private Hosted Zone with the us-west-2 VPC because Private Hosted Zones automatically resolve across all VPCs in the AWS Organization. Promote the Aurora secondary cluster to primary during failover.
  4. D
    Deploy a single NAT Gateway in the us-west-2 region and route all outbound traffic from us-east-1 to it over a VPC peering connection to reduce NAT Gateway costs. Configure Route 53 active-active routing using weighted alias records pointing directly to the EC2 instances, and use Aurora Global Database write endpoint routing for automatic database failover.

Answer

Deploy a NAT Gateway in each Availability Zone in us-east-1, configure a warm standby pattern in us-west-2, associate the Route 53 Private Hosted Zone with the secondary VPC, and orchestrate the failover using Route 53 Application Recovery Controller (ARC) and manual/scripted Aurora cluster promotion.
The correct solution addresses all aspects of the scenario. First, it establishes NAT Gateway redundancy by deploying a NAT Gateway per Availability Zone in the primary region. Second, it implements a warm standby strategy in the secondary region to guarantee a 15-minute RTO. Third, it associates the Route 53 Private Hosted Zone with the secondary VPC so internal DNS resolution remains functional after failover. Fourth, it uses Route 53 Application Recovery Controller (ARC) routing controls and application-level health checks to orchestrate failover, along with promoting the secondary Aurora cluster to primary.

Step-by-Step Solution

1
Ensure AZ-level networking redundancy in the primary region
Deploy a NAT Gateway in each of the public subnets in us-east-1 (us-east-1a, us-east-1b, us-east-1c) and configure the private subnet route tables to send internet-bound traffic to their local AZ's NAT Gateway.
This removes the single point of failure where an outage in a single Availability Zone (us-east-1a) disrupts internet access for the application servers running in the other Availability Zones.
2
Establish the secondary region application and database tier configurations
Deploy a warm standby environment in us-west-2 with application instances and configure the Aurora Global Database replication to the secondary cluster.
Warm standby satisfies the 15-minute RTO requirements, and Aurora Global Database replication maintains an RPO of under 1 minute.
3
Configure internal DNS resolution for the secondary region VPC
Associate the existing Route 53 Private Hosted Zone (PHZ) with the VPC in us-west-2.
Private Hosted Zones are not automatically shared across VPCs. Without this association, internal service names will fail to resolve in us-west-2 after failover.
4
Orchestrate multi-region failover and health checking
Set up Route 53 Application Recovery Controller (ARC) routing controls and application-level health checks that evaluate dependency endpoints. Write automation to promote the secondary Aurora cluster during a failover event.
Route 53 ARC controls allow for safe, coordinated manual or automated traffic shifting without relying solely on simple instance pings, and Aurora Global Database requires manual promotion of the secondary cluster to write mode.

Key Concept

Multi-region disaster recovery, NAT Gateway redundancy, Route 53 Private Hosted Zone association, and Aurora Global Database failover orchestration.
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Topics

Enhancing Reliability and Disaster Recovery