Terraform Basics

Terraform is the most widely used tool for infrastructure as code, and works across every major cloud provider through the same core workflow and syntax.

Providers and resources

A Terraform file (written in HCL, HashiCorp Configuration Language) names a provider - which platform it's talking to - and then declares resources on it:

provider "aws" {
  region = "us-east-1"
}

resource "aws_instance" "web" {
  ami           = "ami-0123456789"
  instance_type = "t3.micro"
}

This says, in full: "talk to AWS's us-east-1 region, and there should exist one t3.micro instance running this AMI, which I'll refer to elsewhere in this config as aws_instance.web."

The core workflow

terraform init      # download the provider plugin, set up the working directory
terraform plan       # show exactly what would change - a dry run
terraform apply      # actually make those changes
terraform destroy    # tear everything this config created back down

terraform plan is the step that makes this trustworthy: it prints precisely what will be created, changed, or destroyed, and nothing actually happens until apply is run and confirmed. No surprises between "what I expected" and "what happened."

Reading a plan

Terraform marks every line of a plan with a symbol - + to create, - to destroy, ~ to update in place. A plan that shows an unexpected - (destroying something you didn't mean to touch) is exactly the kind of mistake this dry-run step exists to catch before it becomes real.

Try it

cat main.tf

When you're ready, hit Mark complete and move to the next lesson.