Lab: Terraform for OVHcloud tested with mock providers

What you will learn in this TP

• Describe OpenStack resources in Terraform
• Write tests with terraform test
• Simulate a provider with mock_provider

Introduction #

What you will learn in this section

• Describe OpenStack resources in Terraform
• Write tests with terraform test
• Simulate a provider with mock_provider

Context. The team wants to review and test every infrastructure change in CI before touching the production project.

Prerequisites: Docker, the AWS CLI (for the S3 API), kubectl, k3d and Terraform 1.7 or later; everything is simulated locally, with no OVHcloud account  ·  Estimated time: 45 min

An automatically tested Terraform module, ready to apply on the Public Cloud.

Hands-on #

Guided steps, with their solution.

1. 1. Write the module

   Why? The instance count variable and validations make the module reusable and safe.

   Create main.tf with a network, a subnet, an HTTPS security group and N instances without public address.

2. 2. Validate

   Why? fmt and validate catch syntax and type errors without a real provider.

   Initialise, format and validate the module.

3. 3. Write tests with a mock provider

   Why? mock_provider returns fake values: the module logic is tested without calling the OpenStack API.

   Create tests/web.tftest.hcl with three tests: instance count, HTTPS rule and rejection of an invalid value.

4. 4. Run the tests

   Why? These tests run in CI on every merge request, without cloud credentials.

   Run the tests, then deliberately break a rule to see the failure.

Difficulty level : ●●●○○ (3/5)