How to modify db subnet group for running aws rds db instance?
RDS DB subnet group is a collection of subnets in VPC. You can select the subnet group while launching RDS .Once you select the subnet group your DB will reside on the specific subnets. If you are not selecting any subnet group AWS will create and use defualt subnet group for the selected VPC.You can also modify the subnet list in default group.
If you are planning to move your DB instance to some other VPC you have to change the DB subnet group.
Unfortunately this option is not available in AWS . Even if you stop the instance also you wont get this option .You have to take a snapshot of particular db instance and create new RDS instance in your desired VPC from snapshot.
But you have option to change DB parameter group and option group.