Terraform Basics

Terraform is an open-source Infrastructure as Code (IaC) tool developed by HashiCorp. It allows users to define, provision, and manage infrastructure across various cloud providers (like AWS, Azure, and GCP) and on-premises environments using a declarative configuration language known as HCL (HashiCorp Configuration Language).

Terraform is popular because:

• It supports multiple cloud providers (AWS, Azure, Google Cloud).

• It provides a unified workflow.

• It maintains an infrastructure state file to track resources.

• It uses a modular approach to manage complex systems.

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Key Terraform Commands

Here are the most common terraform commands you will run into:

1. terraform init

• Purpose: Prepares the working directory for Terraform operations.

• What it does:

  • Downloads provider plugins.

  • Initializes the backend for storing the Terraform state.

  • Verifies the configuration files.

2. terraform validate

• Purpose: Checks the configuration files for syntax or logical errors.

• What it does:

  • Ensures that the configuration is syntactically valid.

  • Validates against the provider's schema but does not connect to the cloud.

3. terraform fmt

• Purpose: Formats the configuration files to match the standard style conventions.

• What it does:

  • Ensures consistent indentation and spacing.

  • Makes code easier to read and maintain.

4. terraform plan

• Purpose: Creates an execution plan showing what actions Terraform will take.

• What it does:

  • Highlights the changes required to achieve the desired state.

  • Outputs actions like resource additions, modifications, or deletions without applying them.

5. terraform apply

• Purpose: Executes the actions defined in the execution plan created by terraform plan.

• What it does:

  • Creates, updates, or deletes resources in the infrastructure.

  • Requires user confirmation before execution unless the -auto-approve flag is used.

6. terraform plan -destroy

• Purpose: Simulates the destruction of resources without actually executing it.

• What it does:

  • Generates a plan detailing which resources will be removed.

  • Useful for previewing the impact of a terraform destroy command.

7. terraform destroy

• Purpose: Removes all resources defined in the Terraform configuration.

• Note: Always run terraform plan -destroy before running any terraform destroy

• What it does:

  • Deletes the infrastructure safely and ensures resources are destroyed in the correct order.

  • You can also target specific resources using the target flag instead of destroying all the resources.

  • eg. terraform destroy --target aws_instance.instance_name

8. terraform import

• Purpose: Brings existing infrastructure into Terraform's management.

• What it does:

  • Adds resources not originally created with Terraform to the state file.

  • Does not generate configuration files automatically; you must write the configuration manually.