What is Relational Database Service (RDS)? (Part-2)

What is Relational Database Service (RDS)?  (Part-2)

What is Multi-AZ in RDS?

  • You can select the Multi-AZ option during the RDS DB instance launch.

  • RDS Service creates standby instances in a different AZ in the same region and configures "Synchronous Replication" between the Primary and Standby.

  • You can not read/write to the standby RDS DB instances.

  • You can not select which AZ in the region will be chosen to create the standby DB instance.

  • You can however view, which AZ is selected after the standby is created.

  • Depending on the instance class, it may take 1 to a few minutes to failover to the standby instance

  • AWS recommends the use of provisioned IOPS instances for Multi-AZ RDS instances.

When Multi-AZ RDS Failover Triggers

  • In case of failure of the Primary DB instance failure.

  • In case of AZ failure.

  • Loss of Primary EC2 instance failure.

  • EBS failure of primary DB instance.

  • The primary DB instance is changed.

  • Patching the OS of the DB instance

  • Manual Failover (in case of Reboot)

Multi-AZ RDS Failover consequences

  • During failover, the CNAME (Canonical Name Record) of the RDS DB instance is updated to Map to the Standby IP address.

  • It is recommended to use the endpoint to reference your DB instances and not its IP address.

  • The CNAME does not change, because the RDS endpoint does not change.

Few More Points

  • The RDS endpoint does not change by selecting the Multi-AZ option. However, the Primary and standby instances will have different IP addresses, as they are in different AZ.

  • It is always recommended that you do not use the IP address to point RDS instances, always use endpoint. By using an endpoint, there will be no change whenever a failover happens.

When do we do Manual Failover?

  • In case of rebooting.

  • This is by selecting the "Reboot with Failover" reboot options on the primary RDS DB instances.

  • A DB instance reboot is required for changes to take effect when you change the DB parameter group or when you change a static DB parameter.

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