RDS Moving a DB instance to a new subnet group

[tommylee9595]

To change VPC for a DB instance, you must create a new subnet group and modify the DB instance to the new subnet group.

this question in the practice exam,

A company uses an Amazon RDS for MariaDB instance in a Multi-AZ deployment for its e-commerce application. To meet the compliance audit, the company’s Database Specialist was required to move the primary DB instance out of its current Availability Zone (ap-southeast-2a) and restrict it to start only in Availability Zones (ap-southeast-2b) and (ap-southeast-2c) in the same Amazon VPC provided by the Network Specialist. The Database Specialist wants to avoid any database data modification and accomplish the task with minimum downtime.

What should the Database Specialist do to meet this requirement?

One of the wrong options, “The option that says: <strong style=”font-family: inherit; font-size: inherit;”>Create a new DB subnet group with appropriate Availability Zones. Modify the MariaDB instance and assign it to a new DB subnet group is incorrect. You cannot move an existing instance to a new DB subnet group.”

I thought you could move instances to new DB subnet group, but here it says you can’t. is this because the question said the setup is Multi-AZ, and you can’t change subnet groups if the setup is Multi-AZ?

Thanks!

[Michael Singer]

Hi. I’m also a little confused on this question. The question doesn’t specify which subnets are in the initial subnet group – but I believe the answer relies on the fact that only 2 subnet groups were in the initial subnet group? Since there were only 2 subnets initially and launching an RDS instance requires 2 subnets – you wouldn’t be able to delete one subnet (since it would only leave you with one) unless you switch to a Single-AZ deployment.

Anyone else have thoughts on this above theory/understanding?

[Joboy-Pineda-TD]

Hello Michael,

Thanks for raising your concern. It is a fair point and the question should have clearly stated the subnet configuration of the Multi-AZ deployment. However, you correctly guessed the implied initial setup which was that the MariaDB instance had subnets in two AZs. I will look into modifying and making the question more specific soon.

Hello tommylee9595,

In case you are still looking for some clarity, here is a link that better explains it: https://aws.amazon.com/premiumsupport/knowledge-center/rds-db-subnet-group/

Best,

Joboy

[Michael Singer]

Thanks Joboy! Appreciate your clarification!