Lab: Infrastructure as Code with Terraform

What you will learn in this TP

• Write a Terraform configuration
• Use plan, apply and state
• Detect and fix drift

Introduction #

What you will learn in this section

• Write a Terraform configuration
• Use plan, apply and state
• Detect and fix drift

Context. Test environments are built by hand and never look alike. You describe them as code, using the Docker provider to work locally without a cloud account.

Prerequisites: Docker and Terraform (or OpenTofu) installed  ·  Estimated time: 40 min

A reproducible environment and a drift detected then fixed.

Hands-on #

Guided steps, with their solution.

1. 1. Write the configuration

   Why? The configuration describes the desired state; Terraform computes the actions.

   In iac-lab/, write main.tf: a network, an nginx image and a variable number of containers exposed on 8081, 8082…, with an output listing the URLs.

2. 2. Initialise, check, plan

   Why? fmt and validate are the CI checks; the plan is what you review in the pull request.

   Initialise the project, check format and validity, then save a plan.

3. 3. Apply and inspect state

   Why? State links code to real resources.

   Apply the plan, test the URLs, then list and inspect state resources.

4. 4. Change the infrastructure

   Why? You change a variable, not commands: the plan shows the exact difference.

   Move to 3 instances with -var, review the plan then apply.

5. 5. Detect drift

   Why? A manual change makes the code wrong: Terraform detects and fixes it.

   Delete a container by hand, detect the drift with -detailed-exitcode (code 2), then re-apply.

6. 6. Destroy

   Why? An environment described as code can be removed and recreated without forgetting anything.

   Destroy everything, check nothing remains, then explain what team work would require (remote backend, locking, CI).

Difficulty level : ●●○○○ (2/5)