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Difficulty: HardDisaster Recovery Strategies

A company hosts a legacy resource planning application in the us-west-2 Region. The application consists of Amazon EC2 instances in an Auto Scaling group behind an Application Load Balancer (ALB) and an Amazon RDS for MySQL DB instance. The company needs to establish a disaster recovery (DR) site in the us-east-1 Region. The DR plan requires a Recovery Point Objective (RPO) of less than 5 minutes and a Recovery Time Objective (RTO) of less than 15 minutes. The configuration must minimize ongoing running costs in the secondary region. Which strategy should a SysOps administrator implement to meet these requirements?

  1. Configure a cross-region read replica of the RDS DB instance in the us-east-1 Region. Deploy the ALB and the VPC infrastructure in the us-east-1 Region, and set the Auto Scaling group minimum and desired capacity to 0. During a DR event, promote the read replica to a standalone DB instance, scale up the Auto Scaling group, and update the Amazon Route 53 DNS failover record to point to the new ALB.Answer
  2. B
    Configure Amazon RDS Multi-AZ replication to replicate the database synchronously between us-west-2 and us-east-1. Deploy an identical active Auto Scaling group and ALB in us-east-1. Rely on RDS Multi-AZ automatic failover to redirect database write traffic and automatically update the application configuration during a regional failure.
  3. C
    Configure a cross-region read replica of the RDS DB instance in us-east-1. Deploy the ALB and active EC2 instances in us-east-1. Set up Amazon Route 53 active-active failover routing without configuring Route 53 health checks on the primary us-west-2 record, relying instead on manual DNS modifications during a failure event.
  4. D
    Use AWS Backup to create daily snapshots of the database and EC2 instances, and replicate them to us-east-1 using Amazon S3 Cross-Region Replication (CRR) on the backup vaults, without enabling S3 versioning on either the source or destination S3 buckets. In a DR event, restore the database and EC2 instances from the snapshots in us-east-1.

Answer

Configure a cross-region read replica of the RDS DB instance in the us-east-1 Region. Deploy the ALB and the VPC infrastructure in the us-east-1 Region, and set the Auto Scaling group minimum and desired capacity to 0. During a DR event, promote the read replica to a standalone DB instance, scale up the Auto Scaling group, and update the Amazon Route 53 DNS failover record to point to the new ALB.
The correct answer represents a Pilot Light disaster recovery strategy. By keeping an Amazon RDS cross-region read replica in the standby region, the data is continuously and asynchronously replicated, meeting the RPO of less than 5 minutes. Having the infrastructure (VPC and ALB) ready but scaling the EC2 Auto Scaling group to 0 minimizes running costs. In the event of a disaster, promoting the read replica and scaling up the Auto Scaling group can be completed within the 15-minute RTO.

Step-by-Step Solution

1
Evaluate the database replication strategy to meet the RPO of less than 5 minutes.
Identify that cross-region RDS MySQL read replicas replicate asynchronously and typically achieve lag times of seconds to minutes, well within the 5-minute RPO.
Backup-and-restore strategies from snapshots fail to meet the 5-minute RPO because daily snapshots could result in up to 24 hours of data loss.
2
Evaluate the application tier deployment strategy to meet the RTO of less than 15 minutes while minimizing cost.
Identify that a Pilot Light strategy (pre-provisioning the network and ALB, and keeping the Auto Scaling group capacity at 0) keeps costs minimal while allowing rapid scaling in minutes.
Warm standby or active-active configurations would run active EC2 instances continuously, increasing ongoing costs unnecessarily. A backup-and-restore from snapshot strategy takes too long to restore the database instance, exceeding the 15-minute RTO.
3
Determine the failover mechanism for database promotion and DNS routing.
Promote the RDS cross-region read replica to a primary standalone DB instance, scale the Auto Scaling group, and update Amazon Route 53 DNS records using failover routing with health checks.
Promoting a read replica changes it to read-write mode in minutes, and DNS failover redirects client traffic to the secondary ALB.

Key Concept

Disaster Recovery Strategies (Pilot Light vs. Backup/Restore/Warm Standby) on AWS
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Topics

Disaster Recovery Strategies

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