Document usage of .terraform.lock.hcl

[hjhsalo]

Document

1. Point to Terraform documentation about lockfile
2. Code in

   smad-deploy-azure/main.tf

   Lines 42 to 56 in 189942a

   	required_providers {
   	azurerm = {
   	source = "hashicorp/azurerm"
   	version = "~> 2.45.1"
   	}
   	kubernetes = {
   	source = "hashicorp/kubernetes"
   	version = ">= 2.0.2"
   	}
   	helm = {
   	source = "hashicorp/helm"
   	version = ">= 2.0.1"
   	}
   	}

   contains version constraints for terraform providers.
   TODO: Check if there are more constraints somewhere else in code.
3. How to update .terraform.lock.hcl (delete and run terraform init OR run terraform init -upgrade)

When a Terraform provider is updated, variables used by the provider might be updated.
E.g.

Error: Unsupported argument

  on modules/k8s_csi_driver_azure/main.tf line 3, in provider "helm":
   3:         load_config_file       = false

An argument named "load_config_file" is not expected here

This is a bit of headache when you cannot simply run tf plan anymore without updating the code.
Maybe Terraform provides a way to lock the dependencies (e.g. in script source) and/or provides a mechanism to output current versions of all dependencies. It might be good to store this output with the code in repo.

[hjhsalo]

This seems to be addresses by Terraform 0.14 which bring support for lock files.
https://www.hashicorp.com/blog/terraform-0-14-introduces-a-dependency-lock-file-for-providers

Seems that JouHouFin already did some of the initial work: smaddis/smad-terraform-azure@2a92344#diff-ad2c33b49112c808ea24699b01e9e020735e894c9438ace109477b3e6098cc43

[hjhsalo]

Let's discuss IRL what is proper way (basically when to fetch dependency updates) to update the lock file.