Can't delete directory

There are a few possible reasons why you may not be able to delete an AWS Directory Service directory if it says it has associated applications:

• Check if there are any AWS Transfer Family servers associated with that directory. Even if the servers are stopped, the directory association remains. You would need to detach or delete any Transfer servers first.

• There could be an application or resource outside of the Transfer Family using that directory. For example, an EC2 instance joined to the domain, a Lambda function using the directory, etc. Check all your resources.

• The directory could have been used for SSO in the past with a disabled/deleted application. Try detaching any inactive identity providers linked to the directory.

• Double check there are no WorkSpaces or AppStream 2.0 fleets using that directory.

• The directory metadata may think an application is still linked even if it is not. Try forcibly disassociating the directory from any applications via the CLI/SDK.

• As a last resort, you can delete the whole AWS account and re-create it if you want to completely remove the directory associations.

So in summary, check Transfer Family servers, look for any other resources integrated with the directory, detach old identity providers, and try disassociating forcefully via API. If all else fails, deleting the AWS account may be the nuclear option to fully remove the directory.