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Difficulty: HardDatabase High Availability

During a scheduled disaster recovery drill, a SysOps Administrator simulates an Availability Zone (AZ) outage for a high-priority application. The application's database tier consists of a primary Amazon RDS for MariaDB DB instance in subnet-A (AZ-1) and a Read Replica in subnet-B (AZ-2). The application connects to the primary DB instance for write operations and to the Read Replica for read operations. During the simulated outage of AZ-1, the application completely loses write access to the database, and no automated failover occurs. What is the root cause of this behavior, and how should the administrator resolve it to ensure automatic write failover?

  1. Read Replicas use asynchronous replication and do not support automatic failover. To resolve this, the administrator must modify the primary DB instance to enable a Multi-AZ deployment, which provides synchronous replication to a standby instance and automated DNS failover.Answer
  2. B
    The Read Replica was not designated as the failover target. To resolve this, the administrator must promote the Read Replica to a standalone DB instance, enable the 'Automatic Failover' option on the primary DB instance, and specify the promoted instance as the failover target.
  3. C
    Amazon Route 53 was not configured to monitor the primary DB instance. To resolve this, the administrator must create a Route 53 active-passive failover routing policy with a health check that automatically routes database write traffic to the Read Replica's endpoint during an outage.
  4. D
    The Read Replica was not configured with the 'Replication Failover' flag enabled. To resolve this, the administrator must modify the Read Replica configuration to set its replication state to synchronous and enable the automatic promotion setting in the RDS console.

Answer

Read Replicas use asynchronous replication and do not support automatic failover. The administrator must modify the primary DB instance to enable a Multi-AZ deployment, which provides synchronous replication to a standby instance and automated DNS failover.
The correct option is correct because Amazon RDS Multi-AZ deployments provide high availability and failover support. In a Multi-AZ deployment, RDS automatically provisions and maintains a synchronous standby replica in a different Availability Zone. If the primary instance fails, RDS automatically performs a failover by updating the DNS record of the DB instance to point to the standby, requiring no changes to the application's connection string. Read Replicas use asynchronous replication and are designed for read scalability, not automatic failover.

Step-by-Step Solution

1
Identify the replication and failover mechanism in the current setup.
The current setup uses a primary RDS instance and an asynchronous Read Replica in a separate AZ.
Understanding the difference between Multi-AZ standbys and Read Replicas is essential to diagnose why automated failover did not occur.
2
Evaluate the failover capabilities of the existing components.
Read Replicas cannot serve as automatic write failover targets in Amazon RDS without manual promotion.
This explains why the simulated outage resulted in a complete loss of write access.
3
Select the appropriate high availability configuration that enables automatic DNS failover.
A Multi-AZ deployment must be enabled on the primary DB instance.
Multi-AZ configuration provides synchronous replication to a standby instance in another AZ and handles automatic DNS failover when the primary instance fails.

Key Concept

Multi-AZ Deployment vs. Read Replicas failover behaviors
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Topics

Database High Availability

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