week1.md

Terraform Beginner Bootcamp 2023 - Week 1

Fixing tags

How to delete local and remote tags on Git

Delete a tag local

$ git tag -d <tag_name>

Delete a tag remote

$ git push --delete origin tagname

Checkout the commit that you want to retag. Grab the SHA from your GitHub histroy

git checkout <SHA>
git tag m.m.p
git push --tags
git checkout main

Root module structure

Our root module structure is as follows:

PROJECT_ROOT
│
├── main.tf               # everything else
├── variables.tf          # stores the structure of input variables
├── providers.tf          # defines required providers & configuration
├── outputs.tf            # stores the outputs
├── terraform.tfvars      # the data of variables we want to load into our Terraform project
└── README.md             # required for root modules

Standard Module Structure

Terraform and Input Variables

Terraform Cloud Variables

In Terraform we can set two kind of variables:

• Enviroment Variables - those you would set in your bash terminal (e.g. AWS credentials)
• Terraform Variables - those that you would normally set in your .tfvars file

We can set Terraform Cloud variables to be sensitive so they are not shown visibliy in the UI.

Loading Terraform Input Variables

Terraform Input Variables

var flag

We can use the -var flag to set an input variable or override a variable in the tfvars file eg. terraform -var user_uuid="my-user_uuid"

var-file flag

• TODO: Document this flag

terraform.tvfars

This is the default file to load in Tterraform variables in bulk

auto.tfvars

• TODO: Document this functionality for Terraform Cloud

order of terraform variables

• TODO: Document which Terraform variables takes precedence

Dealing with configuration drift

If you lose your state files, you most likely have to tear down all you cloud infrastructure manually

You can use Terraform import but it will not work for all cloud resources. You need to check the Terraform providers documentation

Fix missing resourcers with Terraform import

Terraform import

terrafrom import aws_s3_bucket.bucket bucket-name

AWS S3 bucket import

Fix manual configuration

• If someone goes and delete or modifies cloud resource manually through ClickOps.
• If we run Terraform plan with the attampt to put the infrastructure back into the expected state (fixing configuration drift)

Fix using Terraform refresh

terraform apply -refresh-only -auto-approve

Terraform modules

Terraform module structure

It is recommended to place modules in a modules directory when eveloping modules locally

Passing input variables

module "terrahouse_aws" {
  user_uuid = var.user_uuid
  bucket_name = var.bucket_name
}

We can pass input variables into our module. The module has to declare the Terraform variables in its own variables.tf

Module sources

Moudle sources

Using the source we can import the module from various place (locally, GitHub, Terraform Registry)

module "terrahouse_aws" {
  source = "./modules/terrahouse_aws"clear
}

Considerations when using ChatGPT to write Terraform

LLM such as ChatGPT may not be trained on the latest documention or information about Terraform (since it is last update in 2021)

It may likely produce older examples that could be depcrated (this often affects the providers, since they change more often)

Working with files in Terraform

fileexists function

This is a built-in Terrafom function to check the existence of a a file

  validation {
    condition     = fileexists(var.index_html_file_path)
    error_message = "The specified index.html file path is not a valid file or does not exist."
  }

fileexists function

filemd5 function

filemd5 is a variant of md5 that hashes the contents of a given file rather than a literal string.

filemd5 function

Path variable

In Terraform ther is special variable called path that allows us to referece local paths

• pat.module - get the path for the current module
• pat.root - get the path for the root module

Special path variable

resource "aws_s3_object" "index_html" {
  bucket = aws_s3_bucket.website_bucket.bucket
  key    = "index.html"
  source = ${path.root}/public/index.html
}

Terraform locals

Locals allow us to define local variables. They can be very useful when we need to transform data into another format and have it referenced as a variable.

locals {
    s3_origin_id = "MyS3Origin"
}

Local values

Terraform data sources

This allows us to source data from cloud resources. This is useful when we want to reference cloud resources without importing them.

Data sources

data "aws_caller_identity" "current" {}

output "account_id" {
  value = data.aws_caller_identity.current.account_id
}

Example above

Working with JSON

We use the jsonencode function to create the JSON policy inline in the HCL

> jsonencode({"hello"="world"})
{"hello":"world"}

jsonencode

Changing the lifecycle of resources

Meta arguments for lifecycles

Terraform Data

Plain data values such as Local Values and Input Variables don't have any side-effects to plan against and so they aren't valid in replace_triggered_by. You can use terraform_data's behavior of planning an action each time input changes to indirectly use a plain value to trigger replacement.

terraform_data