terraform state mv not creating backups

[mattk-ce]

Terraform Version

0.14.6 - WINDOWS

Expected Behavior

backup file should be created

Actual Behavior

no backup file is created

Steps to Reproduce

0. on windows
1. using s3 remote state - might not be relevant, but is my current configuration
2. terraform state mv -backup="test.backup" -state-out="test/terraform.tfstate" aws_iam_role.test aws_iam_role.test
   OR
   terraform state mv -state-out="test/terraform.tfstate" aws_iam_role.test aws_iam_role.test

Additional Context

Using an s3 backend (might not be relevant, but is my current configuration). When specifying a -backup, no backup file is created when executing a state mv. When not specifying -backup, no backup file is created when executing a state mv

[alisdair]

Hi @mattk-ce, thanks for reporting this.

The remote state storage backends do not support local backups (including the -backup CLI flag), to avoid accidentally exfiltrating sensitive state to a local filesystem. For more on this, see #16464, where the change was made. We recommend using bucket versioning as the S3 backup strategy.

That said, Terraform could be clearer about this. I think we might be able to find somewhere in the docs to clarify this exception, and perhaps we can render a diagnostic warning or error when using -backup with a remote state storage backend.

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