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Difficulty: MediumResilient Database Configurations and High Availability

A financial services company is migrating its transactional application to AWS. The database tier will run on Amazon RDS for PostgreSQL. The company requires a database design that guarantees high availability within a single AWS Region. The design must provide an automatic failover time of less than 60 seconds (Recovery Time Objective) and zero data loss (Recovery Point Objective) during an Availability Zone outage. In addition, the database must support horizontal read scaling during peak hours. Which of the following database configurations meets these requirements?

  1. A
    Deploy a Single-AZ RDS PostgreSQL DB instance and create two Read Replicas in different Availability Zones, configuring the application to promote a Read Replica if the primary fails.
  2. B
    Deploy a Single-AZ RDS PostgreSQL DB instance and use AWS Backup to restore hourly snapshots to a new DB instance in a different Availability Zone during a failure.
  3. Deploy an Amazon RDS Multi-AZ DB cluster with one writer DB instance and two readable standby DB instances across three Availability Zones.Answer
  4. D
    Deploy two Single-AZ RDS PostgreSQL DB instances in different Availability Zones and configure Amazon Route 53 latency-based routing to distribute database write and read traffic.

Answer

Deploy an Amazon RDS Multi-AZ DB cluster with one writer DB instance and two readable standby DB instances across three Availability Zones.
Deploying an Amazon RDS Multi-AZ DB cluster provides a high availability configuration with one primary (writer) DB instance and two readable standby DB instances across three Availability Zones. This deployment uses semi-synchronous replication to ensure zero data loss (RPO of 0) and supports automatic failover in under 35 seconds (meeting the RTO requirement). Furthermore, the readable standby instances allow horizontal scaling of read traffic through the reader endpoint.

Step-by-Step Solution

1
Analyze the requirements for high availability, failover time (RTO < 60s), data loss (RPO = 0), and read scaling.
The solution must support automatic failover in less than 60 seconds, semi-synchronous replication to guarantee zero data loss during an AZ outage, and have readable standby or secondary instances.
This establishes the baseline criteria for filtering out non-compliant architectures.
2
Evaluate Amazon RDS Multi-AZ DB clusters against these criteria.
An RDS Multi-AZ DB cluster consists of one primary (writer) instance and two reader instances across three AZs. It uses semi-synchronous replication to achieve zero data loss (RPO = 0) and offers automatic failover in under 35 seconds, which meets the RTO < 60s constraint.
This confirms that the cluster deployment satisfies all high availability and replication requirements.
3
Evaluate read scaling capabilities of the selected architecture.
Because the standby instances in a Multi-AZ DB cluster are readable, they can actively serve read queries via the reader endpoint, addressing the read scaling constraint without requiring separate asynchronous replicas.
This guarantees that the design scales horizontally under peak workloads.

Key Concept

High Availability and Read Scaling in Amazon RDS Multi-AZ DB Clusters
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Topics

Resilient Database Configurations and High Availability

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