We recently made a change to how provisioners upload files in order to
address an unintended remote code execution vector when using SSH, which
revealed that we had not previously documented well enough the expected
contract for how provisioners upload files to remote systems, and so some
users were depending on unintended consequences of the the bug now fixed.
We are retaining the fix on security-related grounds, but this is a good
prompt to be clearer in the docs about what exactly Terraform is doing
when asked to upload files over SSH and WinRM, so users can understand
what is supported and write their configurations accordingly.
This also includes an additional section to the v1.1 upgrade guide, since
we apparently neglected to document this intentional breaking change in
the first draft of that page.
Of course, provisioners as a whole remain a last resort, and so we're
documenting this as hopefully a helpful aid to those who have no other
option, and not meaning in any way to recommend their use for any new
use-cases.
This is a secondary change to PR #28578
Details:
According to the [Provisioner Connection](https://www.terraform.io/docs/language/resources/provisioners/connection.html) page, provisioners require the connection block.
This change of behavior is shown prominently within a note on the [Provisioner Connection](https://www.terraform.io/docs/language/resources/provisioners/connection.html) page:
> Note: In Terraform 0.11 and earlier, providers could set default values for some connection settings, so that connection blocks could sometimes be omitted. This feature was removed in 0.12 in order to make Terraform's behavior more predictable.
However, this behavioral change is omitted from the [remote-exec provisioner](https://www.terraform.io/docs/language/resources/provisioners/remote-exec.html) page which is where a user will be if they are attempting to follow the prior behavior when this was permissible in versions prior to 0.12. This change prompts the user of that change and directs to the connection page.
Laura Pacilio