What is rds db subnet group in AWS?
- A DB subnet group is a collection of subnets (typically private) that you create in a VPC
- DB instances will reside in the selected subnet group.
- A DB subnet group allows you to specify a particular VPC when creating DB instances.
- Each DB subnet group should have subnets in at least two Availability Zones in a given region
- When creating a DB instance in VPC, you must select a DB subnet group else default group will be selected.
- Amazon RDS uses that DB subnet group and your preferred Availability Zone to select a subnet and an IP address within that subnet to associate with your DB instance.
- If the primary DB instance of a Multi-AZ deployment fails, Amazon RDS can promote the corresponding standby and subsequently create a new standby using an IP address of the subnet in one of the other Availability Zones.
- When Amazon RDS creates a DB instance in a VPC, it assigns a network interface to your DB instance by using an IP address selected from your DB subnet group.
Note : Once RDS DB instance launched with subnet you can not modify the subnet group . You have to re create the Instance if you like to change the subnet group.
You can create subnet group as follows in AWS Console GUI
