docs/cl/bare-metal: Install providers to Terraform 3rd party plugin directory

[ghost]

Listing providers in ~/.terraformrc has been deprecated: https://www.terraform.io/docs/commands/cli-config.html#deprecated-settings

They should be installed into the 3rd party plugins directory instead: https://www.terraform.io/docs/configuration/providers.html#third-party-plugins

Terraform strongly suggests to also name the desired plugin version in the provider configuration.

Testing

$ ls ~/.terraform.d/plugins/
terraform-provider-ct_v0.2.1*  terraform-provider-ct_v0.3.0*  terraform-provider-matchbox_v0.2.2*
$ git clone https://github.com/poseidon/typhoon.git
$ cd typhoon/bare-metal/container-linux/kubernetes/
$ terraform init
Initializing modules...
- module.bootkube
  Getting source "git::https://github.com/poseidon/terraform-render-bootkube.git?ref=5378e166ef7ec44e69fbc2d879dbf048a45a0d09"

Initializing provider plugins...
- Checking for available provider plugins on https://releases.hashicorp.com...
- Downloading plugin for provider "local" (1.1.0)...
- Downloading plugin for provider "null" (1.0.0)...
- Downloading plugin for provider "tls" (1.2.0)...
- Downloading plugin for provider "template" (1.0.0)...

Terraform has been successfully initialized!

You may now begin working with Terraform. Try running "terraform plan" to see
any changes that are required for your infrastructure. All Terraform commands
should now work.

If you ever set or change modules or backend configuration for Terraform,
rerun this command to reinitialize your working directory. If you forget, other
commands will detect it and remind you to do so if necessary.

$ terraform providers
.
├── provider.ct ~> 0.2
├── provider.local ~> 1.0
├── provider.local.default ~> 1.0
├── provider.matchbox ~> 0.2
├── provider.null ~> 1.0
├── provider.null.default ~> 1.0
├── provider.template ~> 1.0
├── provider.template.default ~> 1.0
├── provider.tls ~> 1.0
├── provider.tls.default ~> 1.0
└── module.bootkube
    ├── provider.local (inherited)
    ├── provider.template (inherited)
    └── provider.tls (inherited)

[dghubble]

Thanks for this Dennis!

I've written migration guides and updated tutorials across all platforms in #349. One other point is that the terraform-provider-ct plugin be pinned to what was previously in use via ~/.terraformrc, at least for the initial migration. Work in v1.12.2 ensures later updating the terraform-provider-ct plugin can be done safely for v1.12.2+ clusters (though bare-metal is never affected by the controller destroy problem, so understandable it wasn't a factor in this PR)

[dghubble]

Closed by #349

[ghost]

Thanks!