Possible Failover Reasons for RDS Primary Instance to Standby

Correct Answers: A and E.

In case of long-running queues or Database corruption error, Amazon Primary Instance will not automatically failover to standby instance in different AZ.

You need to manually failover to standby DB instance.

Options B, C, D are incorrect as in these cases, Amazon RDS automatically failover to standby DB instance in different AZ.

For more information on failover scenarios for Amazon RDS, refer to the following URL-

Sure, I'd be happy to explain this in detail.

To start with, Amazon RDS (Relational Database Service) is a managed service that provides an easy way to set up, operate, and scale a relational database in the cloud. It supports multiple database engines, such as MySQL, PostgreSQL, Oracle, SQL Server, and Amazon Aurora. RDS is designed to be highly available and durable by default, with automatic backups, point-in-time recovery, and multi-AZ deployments.

ElastiCache is a managed service that provides an in-memory data store, which can be used to cache frequently accessed data and reduce the load on the primary database. It supports two open-source caching engines: Memcached and Redis. ElastiCache also supports automatic failover in case of node or zone failures.

Now, coming to the question, the scenario described is a stateless highly available application developed using Amazon RDS and ElastiCache. The DB instance is set up in a different AZ (Availability Zone) of the us-west-1 region. This means that the primary DB instance is replicated to a standby DB instance in a different AZ for automatic failover.

The operations director is looking for failover scenarios in which the application will failover to the standby DB instance. In other words, if the primary DB instance fails for some reason, the application should automatically switch over to the standby DB instance to minimize downtime and data loss.

The question asks which of the following is not a possible reason when RDS primary instance failover to standby. Let's go through each option and see if it is a possible reason or not:

A. Long-running queries on primary DB instance: This is a possible reason for RDS failover. If the primary DB instance becomes unresponsive due to long-running queries or deadlocks, the RDS automatic failover mechanism will detect this and promote the standby DB instance to the new primary.

B. Connectivity issues at primary AZ: This is also a possible reason for RDS failover. If there is a network or connectivity issue at the primary AZ, the RDS automatic failover mechanism will detect this and promote the standby DB instance to the new primary.

C. Hardware Failure of primary DB instance: This is a possible reason for RDS failover. If there is a hardware failure at the primary DB instance, such as a disk or CPU failure, the RDS automatic failover mechanism will detect this and promote the standby DB instance to the new primary.

D. Storage failure on primary DB instance: This is also a possible reason for RDS failover. If there is a storage failure at the primary DB instance, such as a corrupted or inaccessible data volume, the RDS automatic failover mechanism will detect this and promote the standby DB instance to the new primary.

E. Database Corruption errors: This is a possible reason for RDS failover. If there is a database corruption error at the primary DB instance, the RDS automatic failover mechanism will detect this and promote the standby DB instance to the new primary.

Therefore, the answer to the question is: A. Long-running queries on primary DB instance and D. Storage failure on primary DB instance are not the possible reasons when RDS primary instance failover to standby.

I hope this explanation helps you understand the concept better.