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Difficulty: Very hardResilient Database Configurations and High Availability

An enterprise runs a critical transactional application backed by an Amazon RDS for PostgreSQL database instance in the us-east-1 Region. The database must sustain an Availability Zone outage with zero data loss (RPO = 0) and automatic failover in less than 60 seconds (RTO < 60s). The enterprise also requires a disaster recovery (DR) solution in the us-west-2 Region with an RPO of less than 5 minutes and an RTO of less than 15 minutes. Which two database configuration actions should the solutions architect take to meet these requirements with the least operational overhead?

  1. Modify the primary database instance to a Multi-AZ DB cluster deployment to support synchronous replication across three Availability Zones and automated failover.Answer
  2. B
    Configure an in-region read replica in another Availability Zone, and create a custom script to automate promotion of the replica if the primary instance becomes unresponsive.
  3. C
    Set up AWS Backup to perform daily database snapshots, copy them to the secondary region, and deploy an AWS CloudFormation template to restore the database in the secondary region during a disaster.
  4. Create an Amazon RDS cross-region read replica in the secondary region to asynchronously replicate data and serve as the promotion target for regional disaster recovery.Answer
  5. E
    Configure Amazon Route 53 latency-based routing to automatically distribute write traffic between the primary instance and the secondary region to achieve active-active database capabilities.

Answer

Modify the primary database instance to a Multi-AZ DB cluster deployment, and create a cross-region read replica in the secondary region.
To achieve high availability with an RPO of 0 and an RTO of less than 60 seconds, the database must be configured with synchronous replication and automated failover. An Amazon RDS Multi-AZ DB cluster deployment provides synchronous replication across three Availability Zones and failover in under 35 seconds, satisfying the primary region HA goals. For cross-region disaster recovery, an Amazon RDS cross-region read replica replicates data asynchronously with very low replication lag (RPO < 5 minutes) and can be promoted to a primary database in the secondary region in under 15 minutes (RTO < 15 minutes) with minimal administrative overhead.

Step-by-Step Solution

1
Evaluate the high availability and failover requirements within the primary region.
The requirements demand an RPO of 0 (no data loss) and an RTO of less than 60 seconds.
An Amazon RDS Multi-AZ DB cluster deployment replicates data synchronously across three Availability Zones, ensuring zero data loss (RPO = 0) and provides automated failover within 35 seconds, which satisfies the local high availability goal.
2
Evaluate the disaster recovery requirements in the secondary region.
The requirements demand an RPO of less than 5 minutes and an RTO of less than 15 minutes.
Creating a cross-region read replica replicates data asynchronously, keeping replication lag under a few seconds (RPO < 5 minutes). The replica can be promoted to a standalone primary database in under 15 minutes (RTO < 15 minutes), meeting the disaster recovery criteria.
3
Analyze and eliminate alternate database replication and recovery configurations.
Using custom promotion scripts for in-region replicas fails synchronous replication and failover RTO requirements. Re-provisioning from snapshots violates the 15-minute RTO. Route 53 latency routing is not supported for active-active writes on RDS PostgreSQL.
This leaves Multi-AZ DB cluster deployment and a cross-region read replica as the only options that satisfy both primary and secondary region constraints with minimal operational overhead.

Key Concept

Amazon RDS Multi-AZ DB clusters provide synchronous replication across three Availability Zones for zero data loss and automated sub-minute failovers, while cross-region read replicas provide asynchronous replication for multi-region disaster recovery with low replication lag and fast promotion capabilities.
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Resilient Database Configurations and High Availability

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