AWS Certified Solutions Architect – Professional — Question 478

A large company has a business-critical application that runs in a single AWS Region. The application consists of multiple Amazon EC2 instances and an Amazon
RDS Multi-AZ DB instance. The EC2 instances run in an Amazon EC2 Auto Scaling group across multiple Availability Zones.
A solutions architect is implementing a disaster recovery (DR) plan for the application. The solutions architect has created a pilot light application deployment in a new Region, which is referred to as the DR Region. The DR environment has an Auto Scaling group with a single EC2 instance and a read replica of the RDS DB instance.
The solutions architect must automate a failover from the primary application environment to the pilot light environment in the DR Region.
Which solution meets these requirements with the MOST operational efficiency?

Answer options

• A. Publish an application availability metric to Amazon CloudWatch in the DR Region from the application environment in the primary Region. Create a CloudWatch alarm in the DR Region that is invoked when the application availability metric stops being delivered. Configure the CloudWatch alarm to send a notification to an Amazon Simple Notification Service (Amazon SNS) topic in the DR Region. Add an email subscription to the SNS topic that sends messages to the application owner. Upon notification, instruct a systems operator to sign in to the AWS Management Console and initiate failover operations for the application.
• B. Create a cron task that runs every 5 minutes by using one of the application's EC2 instances in the primary Region. Configure the cron task to check whether the application is available. Upon failure, the cron task notifies a systems operator and attempts to restart the application services.
• C. Create a cron task that runs every 5 minutes by using one of the application's EC2 instances in the primary Region. Configure the cron task to check whether the application is available. Upon failure, the cron task modifies the DR environment by promoting the read replica and by adding EC2 instances to the Auto Scaling group.
• D. Publish an application availability metric to Amazon CloudWatch in the DR Region from the application environment in the primary Region. Create a CloudWatch alarm in the DR Region that is invoked when the application availability metric stops being delivered. Configure the CloudWatch alarm to send a notification to an Amazon Simple Notification Service (Amazon SNS) topic in the DR Region. Use an AWS Lambda function that is invoked by Amazon SNS in the DR Region to promote the read replica and to add EC2 instances to the Auto Scaling group.

Correct answer: D

Explanation

Option D is the most operationally efficient and resilient solution because it automates the entire failover process using serverless components (CloudWatch, SNS, and Lambda) hosted in the DR Region. Options B and C are flawed because they rely on a cron job running on the primary Region's EC2 instances, which would fail to run if the primary region or instances experience an outage. Option A is incorrect because it requires manual intervention from a systems operator, failing to meet the requirement for automated failover.