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Difficulty: MediumEnhancing Reliability and Disaster Recovery

An enterprise operates a critical reporting application running on Amazon EC2 instances across three Availability Zones in a single VPC within the us-west-2 Region. The instances are managed by an Auto Scaling group behind an Application Load Balancer (ALB). The application reads and writes data to a multi-AZ Amazon RDS for PostgreSQL database. Outbound reporting logs are uploaded to an external partner API via a single NAT Gateway located in one of the public subnets.

The solutions architect must enhance the disaster recovery (DR) posture and reliability of the application. The new DR strategy must support a recovery point objective (RPO) of under 15 minutes and a recovery time objective (RTO) of under 30 minutes in the us-east-1 Region, while minimizing idle resource costs. Additionally, the outbound connectivity must be highly resilient against Availability Zone outages.

Which of the following configurations will meet these requirements? (Select TWO.)

  1. Create an Amazon RDS for PostgreSQL cross-region read replica in the us-east-1 Region, and implement an AWS Lambda function to promote the replica to a standalone DB instance during a failover event.Answer
  2. Deploy a NAT Gateway in each public subnet across all three Availability Zones, and update the route tables of each private subnet to direct egress traffic through the NAT Gateway in its respective Availability Zone.Answer
  3. C
    Configure AWS Backup to take hourly snapshots of the Amazon RDS for PostgreSQL database, automatically copy the snapshots to the us-east-1 Region, and restore the DB instance in us-east-1 during a failover.
  4. D
    Configure a Route 53 failover routing policy pointing to the Application Load Balancers in both regions, and configure Route 53 health checks on the passive region's ALB only, while leaving health checks disabled on the active region's ALB.
  5. E
    Create a Route 53 Private Hosted Zone (PHZ) for the internal API endpoints in the us-west-2 VPC, but omit associating the PHZ with the us-east-1 VPC, relying instead on inter-region VPC peering to automatically resolve DNS queries across regions.

Answer

The correct configurations are to create an Amazon RDS for PostgreSQL cross-region read replica in the recovery region and automate its promotion, and to deploy a NAT Gateway in each Availability Zone and update the route tables of each private subnet to route outbound traffic through its local NAT Gateway.
The correct configurations address both disaster recovery and reliability. The option to create and automate the promotion of an RDS cross-region read replica handles the database DR requirements (RPO < 15 mins, RTO < 30 mins) cost-effectively. The option to deploy a NAT Gateway in each public subnet per Availability Zone removes the egress network single point of failure, satisfying the AZ redundancy requirement.

Step-by-Step Solution

1
Evaluate the database recovery requirements (RPO < 15 minutes, RTO < 30 minutes, minimize cost).
Identify that cross-region read replication for Amazon RDS PostgreSQL provides low-latency asynchronous replication that meets the low RPO, while promoting the replica via automation meets the RTO without incurring the high costs of active-active setups.
RDS cross-region read replicas replicate data asynchronously to the target region, maintaining a recovery point within seconds or minutes, and can be promoted to standalone instances quickly.
2
Evaluate the outbound connectivity reliability requirement.
Identify that the current single NAT Gateway is a single point of failure (SPOF) for AZ outages, and deploying a NAT Gateway in each Availability Zone removes this SPOF.
By having a NAT Gateway per Availability Zone, a failure in one AZ does not impact outbound traffic originating from the other AZs.

Key Concept

Disaster recovery planning using cross-region read replicas for low RTO/RPO database failover combined with multi-AZ NAT Gateway redundancy to prevent egress connectivity single points of failure.
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Topics

Enhancing Reliability and Disaster Recovery