How to reference Terraform Environment variable in providers?

I have a gitlab pipeline that runs some terraform, so say I have a pipeline that declares

Plan (Example):
  variables:
    TF_VAR_myenvvariable: /home/$example

So now inside my Terraform Project under providers.tf

I have

provider "docker" {
...

    registry_auth {
        address     = "example.com"
        config_file = "${TF_VAR_myenvvariable}/docker.json"
    }
}

How do I get this to work? It's not working. I can't use the var.myenvvariable because you can't use variables in the providers block.

There are at least 2 docker providers in the Terraform registry that seem compatible to your provider configuration:

• kreuzwerker/docker
• calxus/docker

You haven't specified which one you're using. Given these are very similar, they probably work exactly the same way.

Many Terraform providers allow you to omit properties and use environment variables instead. For example, when using calxus/docker provider you can set the DOCKER_HOST instead of setting the config_file property.

So you can configure your gitlab pipeline as follows:

Plan (Example):
  variables:
    DOCKER_HOST: /home/$example

Provider configuration:

provider "docker" {
  # ...

  registry_auth {
    address = "example.com"
  }
}

Or, as an alternative, use username and password:

Plan (Example):
  variables:
    DOCKER_REGISTRY_USER: myuser
    DOCKER_REGISTRY_PASS: mypassword

Provider configuration:

provider "docker" {
  # ...

  registry_auth {
    address = "example.com"
  }
}