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.
Fixed a bug in which an example custom provider would be saved as "terraform-provider-custom-v0.0.1" instead of "terraform-provider-custom_v0.0.1". Not an issue when running the bundle on TFE, but a problem when trying to run a terraform bundle locally.
To make it easier to include third-party plugins in generated bundles, we'll now search a local directory for available plugins and skip attempting to install from releases.hashicorp.com if a dependency can be satisfied locally.
Normally "terraform init" will download and install the plugins necessary
to work with a particular configuration, but sometimes Terraform is
deployed in a network that, for one reason or another, cannot access the
official plugin repository for automatic download.
terraform-bundle provides an alternative method, allowing the
auto-download process to be run out-of-band on a separate machine that
_does_ have access to the repository. The result is a zip file that can
be extracted onto the target system to install both the desired
Terraform version and a selection of providers, thus avoiding the need
for on-the-fly plugin installation.
This is provided as a separate tool from Terraform because it is not
something that most users will need. In the rare case where this is
needed, we will for the moment assume that users are able to build this
tool themselves. We may later release it in a pre-built form, if it proves
to be generally useful.
It uses the same API from the plugin/discovery package is is used by the
auto-install behavior in "terraform init", so plugin versions are resolved
in the same way. However, it's expected that several different Terraform
configurations will run from the same bundle, so this tool allows the
bundle to include potentially many versions of the same provider and thus
allows each Terraform configuration to select from the available versions
in the bundle, avoiding the need to upgrade all configurations to new
provider versions in lockstep.
