website: Reconcile docs about plugin discovery and downloading
I'm attempting to keep things simple for normal users while making sure we've
got the full behavior written down somewhere for plugin developers.
This commit doesn't stand alone; it's paired with a commit in the
terraform-website repo, to deal with some related content in the "extend"
section.
In the 0.10 release we added an opt-in mode where Terraform would prompt
interactively for confirmation during apply. We made this opt-in to give
those who wrap Terraform in automation some time to update their scripts
to explicitly opt out of this behavior where appropriate.
Here we switch the default so that a "terraform apply" with no arguments
will -- if it computes a non-empty diff -- display the diff and wait for
the user to type "yes" in similar vein to the "terraform destroy" command.
This makes the commonly-used "terraform apply" a safe workflow for
interactive use, so "terraform plan" is now mainly for use in automation
where a separate planning step is used. The apply command remains
non-interactive when given an explicit plan file.
The previous behavior -- though not recommended -- can be obtained by
explicitly setting the -auto-approve option on the apply command line,
and indeed that is how all of the tests are updated here so that they can
continue to run non-interactively.
In #15884 we adjusted the plan output to give an explicit command to run
to apply a plan, whereas before this command was just alluded to in the
prose.
Since releasing that, we've got good feedback that it's confusing to
include such instructions when Terraform is running in a workflow
automation tool, because such tools usually abstract away exactly what
commands are run and require users to take different actions to
proceed through the workflow.
To accommodate such environments while retaining helpful messages for
normal CLI usage, here we introduce a new environment variable
TF_IN_AUTOMATION which, when set to a non-empty value, is a hint to
Terraform that it isn't being run in an interactive command shell and
it should thus tone down the "next steps" messaging.
The documentation for this setting is included as part of the "...in
automation" guide since it's not generally useful in other cases. We also
intentionally disclaim comprehensive support for this since we want to
avoid creating an extreme number of "if running in automation..."
codepaths that would increase the testing matrix and hurt maintainability.
The focus is specifically on the output of the three commands we give in
the automation guide, which at present means the following two situations:
* "terraform init" does not include the final paragraphs that suggest
running "terraform plan" and tell you in what situations you might need
to re-run "terraform init".
* "terraform plan" does not include the final paragraphs that either
warn about not specifying "-out=..." or instruct to run
"terraform apply" with the generated plan file.
This guide covers assorted best practices and caveats for running
Terraform within orchestration tools and other automation. It provides
general examples and guidance, with the intent that this advice can be
adapted by the reader to a concrete implementation within a selected
orchestration tool.
This guide is based both on our in-house experience with Terraform
Enterprise and on in-house solutions we are aware of in certain
organizations.
