About RDS redundancy (Multi-AZ)
Launching an instance of the Oracle database type in RDS to achieve a multi-AZ configuration can increase the availability of the website in the event of a database server failure.
Amazon RDS multi-AZ deployments provide extended availability and persistence of database (DB) instances, making them a natural fit for operational database workloads.
When you provision a Multi-AZ DB instance, Amazon RDS automatically creates a primary DB instance and simultaneously replicates the data to a standby instance in a different availability zone (AZ) .
Each availability zone operates on its own, physically distinct infrastructure. It is also designed to maintain high reliability.
In the event of an infrastructure failure, Amazon RDS will automatically failover to a standby (or read replica in the case of Amazon Aurora) so that the database can resume operation as soon as the failover is complete.
Amazon RDS provides high availability and failover support for DB instances using multi-AZ deployments.
Using the RDS console, multi-AZ deployments can be created simply by enabling multi-AZ when creating DB instances.
Using the console, an existing DB instance can be converted to a multi-AZ deployment by modifying the DB instance and specifying the multi-AZ option.
Multi-AZ deployments can also be specified using the AWS CLI or Amazon RDS API.