Fail over an RDS PostgreSQL cross-Region read replica behind a Route 53 failover record

SAP-C02 By islever Editorial Last updated

Design a solution to ensure business continuity. Design a strategy to meet reliability requirements. Architect network connectivity strategies.

Short answer

AD Use a cross-Region read replica promoted by Lambda on failover and a Route 53 failover routing policy for the database record.

Question

A solutions architect must implement a multi-Region architecture for an Amazon RDS for PostgreSQL database that supports a web application. The database launches from an AWS CloudFormation template that includes AWS services and features that are present in both the primary and secondary Regions. The database is configured for automated backups, and it has an RTO of 15 minutes and an RPO of 2 hours. The web application is configured to use an Amazon Route 53 record to route traffic to the database. Which combination of steps will result in a highly available architecture that meets all the requirements? (Choose two.)
  1. Create a cross-Region read replica of the database in the secondary Region. Configure an AWS Lambda function in the secondary Region to promote the read replica during a failover event. Correct Answer
  2. In the primary Region, create a health check on the database that will invoke an AWS Lambda function when a failure is detected. Program the Lambda function to recreate the database from the latest database snapshot in the secondary Region and update the Route 53 host records for the database.
  3. Create an AWS Lambda function to copy the latest automated backup to the secondary Region every 2 hours.
  4. Create a failover routing policy in Route 53 for the database DNS record. Set the primary and secondary endpoints to the endpoints in each Region. Correct Answer
  5. Create a hot standby database in the secondary Region. Use an AWS Lambda function to restore the secondary database to the latest RDS automatic backup in the event that the primary database fails.

Key Takeaways

A cross-Region read replica replicates continuously rather than on a schedule, so the RPO is far tighter than the two-hour requirement, and promotion takes on the order of a minute, which is what makes the fifteen-minute RTO achievable without a restore from backup.

A web application uses an RDS for PostgreSQL database that is created from a CloudFormation template and configured with automated backups. The target is a multi-Region architecture with an RTO of fifteen minutes and an RPO of two hours, and the application resolves the database through a Route 53 record.

Common mistake: Satisfying the RPO with a scheduled backup copy and calling it a standby. Copying the latest automated backup every two hours leaves nothing running in the secondary Region to be promoted, so a failover would still require a restore that blows the fifteen-minute RTO.

Expert Analysis

Why the Answer Is Correct

A cross-Region read replica continuously replicates the primary's transaction log to the secondary Region, so the data loss on failover is bounded by replication lag rather than by a backup schedule, which comfortably satisfies the two-hour RPO. Promoting that replica takes on the order of a minute, which is what makes the fifteen-minute RTO reachable, and a Lambda function in the secondary Region can perform the promotion automatically when a failover event occurs. The Route 53 failover routing policy in D then supplies the client-side failover: with primary and secondary endpoints set to the records in each Region and health evaluation enabled, applications resolving the database through that record are directed to the promoted instance in the secondary Region. Together they give a highly available design meeting both objectives.

Why the Other Options Are Wrong

B: Recreating the database from the latest snapshot in the secondary Region takes far longer than fifteen minutes, because it must copy snapshots, restore them, and update records, so the RTO is not met. C: Copying the latest automated backup every two hours meets the RPO only if the copy completes reliably within that window, and it does not address failover at all because there is no standby database running, so nothing exists to promote and the RTO is not achievable. E: A hot standby restored from an RDS automatic backup has the same RTO problem as B, and it also depends on automated backups having been copied to the secondary Region, which the option does not specify.

Community Comment Notes

The community voted 100 to 0 for A and D, and the top-voted comment noted that this is a classic question. Commenters broke down why the others fail in the same terms: C meets the RPO but provides no standby to fail over to, B will not meet the fifteen-minute RTO, and E is incomplete because it does not say how the backups reach the secondary Region.

Official Reference

https://docs.aws.amazon.com/AmazonRDS/latest/UserGuide/USER_PostgreSQL.Replication.ReadReplicas.html

This link opens the official vendor documentation in a new tab.

Community Votes

AD
100%

100% of anonymous learners picked answer AD. Votes are pick records left by other test-takers — they are not the verified answer.

Discussion 5 contributions

Compiled from public community threads and reader submissions, lightly edited for clarity. Handles and vote tallies are shown as recorded, and comments reflect the views of individual contributors.

From public community threads 5

  1. Dgix 👍 2
    A is required to meet the RTO as well as the RPO. B will not meet the RTO. C meets the RPO but doesn't handle failover D handles failover E is incomplete and says nothing of how backups arrive in the secondary region and will most likely not meet the RTO.
  2. CMMC 👍 2
    cross region read replicate at secondary region, promote during failover, together with Route 53 failover routing policy
  3. AzureDP900 👍 1
    Here's a breakdown of the correct steps: Step A: Cross-Region Read Replica: Create a cross-Region read replica of the database in the secondary Region. This ensures continuous data replication between Regions, minimizing data loss and ensuring business continuity. Step D: Failover Routing Policy: Create a failover routing policy in Route 53 for the database DNS record. Set the primary and secondary endpoints to the endpoints in each Region. This allows for swift failover to the standby database in case of a failure. These two steps together ensure: Continuous data replication between Regions, minimizing data loss and ensuring business continuity. Swift failover to the standby database in case of a failure, with minimal disruption to services.
  4. Russs99 👍 1
    Option C involves copying the latest automated backup to the secondary Region every 2 hours, which does not provide a standby database instance and may not meet the RTO requirement.
  5. trungtd 👍 2
    Classic question

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