Terraform Overview — Terraform Basics | CertQnA

Terraform, created by HashiCorp and open-sourced in 2014, is the most widely adopted cloud infrastructure provisioning tool. It uses a declarative language (HCL), a provider plugin model, and a state file to manage infrastructure across hundreds of cloud platforms and services.

How Terraform Works

The Terraform workflow has four phases:

Write: Define infrastructure in .tf files using HCL (HashiCorp Configuration Language)
Init: terraform init downloads providers and initialises the backend
Plan: terraform plan compares desired state (code) to current state (state file) and shows what will change
Apply: terraform apply executes the changes — creates, updates, or destroys resources

Providers

Terraform uses a provider plugin model. Providers are plugins that define the resources and data sources for a specific platform:

hashicorp/aws — 1,000+ AWS resources
hashicorp/google — GCP resources
hashicorp/azurerm — Azure resources
hashicorp/kubernetes — Kubernetes resources
hashicorp/helm — Helm releases
hashicorp/github — GitHub repositories, teams, webhooks
...1,000+ providers on the Terraform Registry

Providers are downloaded from the Terraform Registry during terraform init.

Terraform State

Terraform maintains a state file (terraform.tfstate) that maps your configuration to real-world resources. State is how Terraform knows:

Which resources it manages (vs resources that exist but weren't created by Terraform)
What the current configuration of those resources is
What needs to change when you run plan

By default, state is stored locally. For teams, use a remote backend (S3, Terraform Cloud) to share state and enable locking.

Terraform vs Other IaC Tools

Feature	Terraform	CloudFormation	Pulumi	Ansible
Multi-cloud	Yes	AWS only	Yes	Yes
Language	HCL	YAML/JSON	TS/Python/Go	YAML
State management	Yes (state file)	Managed by AWS	Yes	No (idempotent tasks)
Provisioning	Excellent	Excellent (AWS)	Excellent	Good
Config management	Limited	No	Limited	Excellent
Learning curve	Low	Medium	Depends on language	Low

Terraform vs OpenTofu

In August 2023, HashiCorp changed Terraform's licence from MPL 2.0 (open source) to BSL (Business Source Licence), which restricts commercial use. In response, the community forked Terraform as OpenTofu, donated to the Linux Foundation, and maintained as a truly open-source alternative.

OpenTofu 1.x is compatible with Terraform 1.5.x syntax
Both tools use the same HCL syntax and provider ecosystem
OpenTofu is the tool most open-source projects are migrating to

For learning purposes, HCL skills transfer directly between Terraform and OpenTofu.

Terraform CLI Commands Overview

terraform init          # initialise directory, download providers
terraform validate      # check syntax and configuration
terraform fmt           # format code to canonical style
terraform plan          # preview changes
terraform apply         # apply changes
terraform destroy       # destroy all managed resources
terraform output        # show output values
terraform state list    # list resources in state
terraform import        # import existing resource into state
terraform workspace     # manage named workspaces

Next: HCL — the language you write Terraform configurations in.