A utility company operates a critical smart grid telemetry application across two accounts… — AWS Certified Solutions Architect - Professional

A utility company operates a critical smart grid telemetry application across two accounts in an AWS Organization: a Network account and a Workload account. The application currently runs in a single active Region (us-west-2). In the Workload account, the application tier consists of Amazon ECS tasks running on AWS Fargate in private subnets, fronted by an internal Application Load Balancer (ALB). The database tier runs on an Amazon Aurora PostgreSQL database cluster. The Workload VPC is connected to a central VPC in the Network account via an AWS Transit Gateway. Internal DNS resolution for grid.utility.internal is managed via a Route 53 Private Hosted Zone (PHZ) in the Network account, associated with the Network VPC.

The company needs to establish a Warm Standby disaster recovery (DR) solution in a secondary Region (us-east-1). The DR solution must support a Recovery Point Objective (RPO) of 5 minutes and a Recovery Time Objective (RTO) of 15 minutes.

Which architectural modification will meet these requirements while ensuring reliable failover and DNS resolution?

A
Configure hourly AWS Backup copy jobs to replicate Aurora snapshots from the active Region to the standby Region. Deploy the ECS cluster and Fargate task definitions in the standby Region with a desired capacity of zero. Associate the standby VPC with the Route 53 Private Hosted Zone using a cross-account IAM role. Deploy a single NAT Gateway in the standby VPC's public subnet to save costs. During failover, restore the database from the latest snapshot, scale up the ECS tasks, and manually update the Route 53 Private Hosted Zone records.
B
Promote the database to an Amazon Aurora Global Database with the primary cluster in the active Region and a secondary cluster in the standby Region. Pre-deploy the ECS tasks at a minimal scale in the standby Region's VPC. Connect the standby VPC to the Transit Gateway, relying on Transit Gateway's transitive routing to resolve DNS queries via the existing association in the Network account without creating a new VPC association for the Private Hosted Zone. Deploy a NAT Gateway in each Availability Zone of the standby VPC. Configure Route 53 active-passive failover routing records pointing to the primary and secondary Application Load Balancers.
Promote the database to an Amazon Aurora Global Database with the primary cluster in the active Region and a secondary cluster in the standby Region. Pre-deploy the ECS tasks at a minimal scale in the standby Region's VPC. Submit a VPC association authorization from the Network account for the standby VPC, and associate the standby VPC with the Route 53 Private Hosted Zone from the Workload account. Deploy a NAT Gateway in each Availability Zone of the standby VPC. Configure Route 53 Application Recovery Controller (ARC) routing controls to orchestrate failover, using Route 53 health checks associated with the routing controls to manage traffic redirection.Answer
D
Promote the database to an Amazon Aurora Global Database with the primary cluster in the active Region and a secondary cluster in the standby Region. Pre-deploy the ECS tasks at a minimal scale in the standby Region's VPC. Submit a VPC association authorization from the Network account for the standby VPC, and associate the standby VPC with the Route 53 Private Hosted Zone from the Workload account. Deploy a NAT Gateway in each Availability Zone of the standby VPC. Configure Route 53 failover records with Evaluate Target Health set to false and without Route 53 health checks, relying on AWS Transit Gateway route propagation to automatically redirect user traffic when the active Region becomes unreachable.

Answer

The correct recommendation is to promote the database to an Amazon Aurora Global Database, pre-deploy ECS tasks at a minimal scale in the standby Region, authorize and associate the standby VPC with the Route 53 Private Hosted Zone cross-account, deploy redundant NAT Gateways per Availability Zone, and use Route 53 Application Recovery Controller (ARC) routing controls to orchestrate failover.

The correct recommendation ensures that all constraints of the multi-account, multi-region environment are met. Using Amazon Aurora Global Database keeps replication lag under a second, meeting the 5-minute RPO. The Warm Standby pattern with ECS Fargate tasks running at a minimal scale allows the application to scale up within the 15-minute RTO. Authorizing and associating the standby VPC cross-account ensures that ECS tasks in the standby Region can resolve grid.utility.internal. NAT Gateways in each Availability Zone ensure outbound connectivity is highly available, avoiding single points of failure. Finally, Route 53 ARC routing controls provide safe, deterministic failover management.

Step-by-Step Solution

Implement low-latency database replication across Regions.

Amazon Aurora Global Database provides physical, storage-based replication with latency typically under 1 second.

This satisfies the strict 5-minute Recovery Point Objective (RPO) constraint.

Configure the standby application tier compute resources.

Pre-deploying ECS tasks at a minimal scale ensures a Warm Standby is ready to accept traffic and can be scaled out in minutes.

This enables meeting the 15-minute Recovery Time Objective (RTO) constraint.

Establish secure cross-account internal DNS resolution.

Authorize the standby VPC association from the Network account containing the Private Hosted Zone (PHZ), then associate it from the Workload account.

VPCs must be explicitly associated with a Route 53 Private Hosted Zone to resolve its records; this cannot be done transitively over AWS Transit Gateway.

Ensure egress redundancy in the standby Region.

Deploy a NAT Gateway in each Availability Zone of the standby VPC.

This prevents a single NAT Gateway failure from disabling outbound connectivity for the entire application tier in the standby Region.

Configure the global routing failover mechanism.

Implement Route 53 Application Recovery Controller (ARC) routing controls linked to Route 53 health checks.

This provides a highly reliable failover controller that can execute coordinated failovers across Regions without relying on local resource health check loops.

Key Concept

Multi-region disaster recovery planning requires coordinating storage replication (RPO), compute readiness (RTO), cross-account Private Hosted Zone DNS associations, and robust health-checked routing failovers.

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