In AWS Cost Management, when we group costs by "Instance Type" for RDS Service I can see the No Instance Type *** is getting a really large portion of the total cost. In my case, it's around 45%.
At the bottom of the page we can see an explanation:
***This category includes costs (e.g., data transfer in/out) that are not directly attributable to a specific Instance Type.
What can be part of that except data transfer? Provisioned IOPS maybe?
To understand the “No Instance type”, please choose the Group by from the Instance type to the Usage type. you can see the cost StorageIOUsage, instancetype , ChargedBackupUsage, etc.
just give a try you will get the more detail..