The most suitable option is Create Amazon Machine Images (AMIs) from the EC2 instances and replicate them to a different AWS Region. Use AWS CloudFormation templates to automate infrastructure provisioning during recovery. This strategy follows a pilot light disaster recovery model: only essential resources (like AMIs and templates) are maintained in the secondary Region until a disaster occurs. When triggered, CloudFormation can quickly and reliably provision the necessary infrastructure, meeting the sub-4-hour RTO while keeping operational costs low during normal business operations.

The option Generate AMIs from the EC2 instances and copy them to a secondary Region. Use AWS Lambda functions and custom automation scripts to orchestrate failover deployment is operationally more complex. While this could work, maintaining custom automation increases the burden of upkeep and risk of failure compared to the declarative, version-controlled approach of CloudFormation.

The choice Deploy EC2 instances in a backup Region and keep them continuously running to ensure immediate availability represents a warm standby or even active-active strategy. This guarantees a quick failover but consumes significantly more resources and costs during normal operationscontradicting the requirement to minimize AWS resource usage.

The option Provision a duplicate EC2 environment in a second Availability Zone and keep it fully operational for high availability provides fault tolerance within the same Region but doesnt protect against a full Regional outage. Since the scenario requires cross-Region DR, this doesnt meet the fundamental requirement.

This question is important for evaluating your understanding of disaster recovery strategies and their trade-offs. The phrase RTO of less than 4 hours points to either a pilot light or warm standby solution. The requirement to use minimal resources in normal conditions favors a pilot light model, ideally paired with automated, infrastructure-as-code tools like CloudFormation.

The trap in this question is the allure of Lambda and custom scripts, which may sound flexible but introduce more maintenance and room for error. CloudFormation is purpose-built for repeatable infrastructure deployment, making it both simpler and more reliable under pressure.

Full AWS Practitioner Certification Question