terraform.md

What is Terraform?

• Terraform is a tool that facilitates "Infrastructure as Code" (aka "IaC")

How do I use Terraform?

• terraform code (stored in files that end in .tf) is declarative code for the infrastructure you want
• terraform the command line tool is how you deploy that code, which creates the infrastructure you want
• Working from "fine" Grain to "coarse" Grain:
  • resource:
    • resources are the "atom"/finest Grain unit of terraform - a resource block defines an individual infrastructure object.
      • The following defines an AWS RedShift cluster (documentation)

        resource "aws_redshift_cluster" "example" {
          cluster_identifier = "tf-redshift-cluster"
          database_name      = "mydb"
          master_username    = "exampleuser"
          master_password    = "Mustbe8characters"
          node_type          = "dc1.large"
          cluster_type       = "single-node"
        }

      • You can have one or multiple resource blocks in one .tf file.
  • variable:
    • Input variables are analogous to function arguments in a general purpose programming language. These variables are used as inputs to resources:

      variable "serverless_base_capacity" {} 
      variable "serverless_max_capacity" {} 
      resource "aws_redshiftserverless_workgroup" "analytics_wg" {
        base_capacity = var.serverless_base_capacity
        max_capacity = var.serverless_max_capacity
        # ...other arguments...
      }

  • module:
    • A module is a collection of resources that are grouped together. There are 2 main subdivisions of modules:
      • 1. The Root Module
        • The Root module is at least one, but possibly multiple .tf files in the same working directory.
          • This can go by other names such as a "configuration" or "group" (Concert naming convention).
      • 2. Reusable Module
        • re-usable modules are also groups resources. However, creating
        • re-usable modules can be thought off as terraform's version of a function.
  • output:
    • Output values are an analogous to return values in general purpose programming languages.
    • The main use case of an output is when you are developing a Reusable Module; you would declare an output in the Reusable Module code, and then when you call that Reusable Module (as a Child Module (terraform lingo)), you can reference that output in other parts of your Root Module/configuration.