One of the pre-requisites for using of AWS DMS is having configured a subnet group, which is a collection of subnets that will be used by the DMS Replication Instance.
Go to AWS Console > Services > Database Migration Service > Subnet groups and click on Create subnet group button.
In the Create replication subnet group enter the following parameter values:
|Description||Target VPC Subnet Group for DMS|
|Add subnets||select TargetVPC-private-a-db, TargetVPC-private-b-db|
Click on the Create subnet group button
In this step you will create an AWS Database Migration Service Replication Instance that initiates the connection between the source and target databases, transfers the data, and caches any changes that occur on the source database during the initial data load.
Inside AWS Console, go to Services and Database Migration Service.
Click on Replication instances and then on the Create replication instance button.
On the Create replication instance screen configure a new replication instance with the following parameter values:
|Description||DMS replication instance|
|Allocated storage (GB)||50|
Like on the screenshot below.
In the Advanced security and network configuration, make sure to select the replication subnet group, Availability zone (us-west-2a) and the replication instance security group that you created earlier.
Click Create button.
If you get an error saying “SYSTEM ERROR MESSAGE: Cannot create a dms.t2.medium replication instance”, create the DMS replication instance again but select us-west-2b Availability Zone and if this doesn’t help - select larger instance class.