Starter kit for a Terraform module

This is a Starter kit to help with the creation of Terraform modules. The basic structure of a Terraform module is fairly simple and consists of the following basic values:

• README.md - provides a description of the module
• main.tf - defiens the logic for the module
• variables.tf (optional) - defines the input variables for the module
• outputs.tf (optional) - defines the values that are output from the module

Beyond those files, any other content can be added and organized however you see fit. For example, you can add a scripts/ directory that contains shell scripts executed by a local-exec null_resource in the terraform module. The contents will depend on what your module does and how it does it.

Instructions for creating a new module

1. Update the title and description in the README to match the module you are creating
2. Fill out the remaining sections in the README template as appropriate
3. Implement your logic in the in the main.tf, variables.tf, and outputs.tf
4. Use releases/tags to manage release versions of your module

Module overview

Description

Description of module

Note: This module follows the Terraform conventions regarding how provider configuration is defined within the Terraform template and passed into the module - https://www.terraform.io/docs/language/modules/develop/providers.html. The default provider configuration flows through to the module. If different configuration is required for a module, it can be explicitly passed in the providers block of the module - https://www.terraform.io/docs/language/modules/develop/providers.html#passing-providers-explicitly.

Software dependencies

The module depends on the following software components:

Command-line tools

• terraform >= v0.15

Terraform providers

• IBM Cloud provider >= 1.5.3

Module dependencies

This module makes use of the output from other modules:

• Cluster - github.com/cloud-native-toolkit/terraform-ibm-container-platform.git
• Namespace - github.com/cloud-native-toolkit/terraform-cluster-namespace.git
• etc

Example usage

module "argocd" {
  source = "github.com/cloud-native-toolkit/terraform-tools-argocd.git"

  cluster_config_file = module.dev_cluster.config_file_path
  cluster_type        = module.dev_cluster.type
  app_namespace       = module.dev_cluster_namespaces.tools_namespace_name
  ingress_subdomain   = module.dev_cluster.ingress_hostname
  olm_namespace       = module.dev_software_olm.olm_namespace
  operator_namespace  = module.dev_software_olm.target_namespace
  name                = "argocd"
}

Anatomy of the Terraform module

An automation modules is created from a template repository that includes a skeleton of the module logic and the automation framework to validate and release the module.

Module logic

The module follows the naming convention of terraform modules:

• main.tf - The logic for the module. In the template module, this file is empty.
• variables.tf - The input variables for the module.
• outputs.tf - The output variables for the module. Output variables are used to pass values to downstream modules.
• version.tf - The minimum required terraform version. Currently, this is defaulted to v0.15. If any terraform providers are required by the module they would be added here as well.
• module.yaml - The metadata descriptor for the module. Each of the automation modules provides a metadata file that describes the name, description, and external dependencies of the module. Metadata for the input variables can also be provided. When a release of the module is created, an automated workflow will supplement the contents of this file with the input and output variables defined in variables.tf and outputs.tf and publish the result to index.yaml on the gh-pages branch.
• README.md - The documentation for the module. An initial readme is provided with instructions at the top and a template for the module documentation at the bottom.

Module automation

The automation modules rely heavily on GitHub Actions automatically validate changes to the module and release new versions. The GitHub Action workflows are found in .github/workflows. There are three workflows provided by default:

Verify and release module (verify.yaml)

This workflow runs for pull requests against the main branch and when changes are pushed to the main branch.

on:
  push:
    branches: [ main ]
  pull_request:
    branches: [ main ]

The verify job checks out the module and deploys the terraform template in the test/stages folder. (More on the details of this folder in a later section.) It applies the testcase(s) listed in the strategy.matrix.testcase variable against the terraform template to validate the module logic. It then runs the .github/scripts/validate-deploy.sh to verify that everything was deployed successfully. Note: This script should be customized to validate the resources provisioned by the module. After the deploy is completed, the destroy logic is also applied to validate the destroy logic and to clean up after the test. The parameters for the test case are defined in https://github.com/cloud-native-toolkit/action-module-verify/tree/main/env. New test cases can be added via pull request.

The verifyMetadata job checks out the module and validates the module metadata against the module metadata schema to ensure the structure is valid.

The release job creates a new release of the module. The job only runs if the verify and verifyMetadata jobs completed successfully AND if the workflow was started from a push to the main branch (i.e. not a change to a pull request). The job uses the release-drafter/release-drafter GitHub Action to create the release based on the configuration in .github/release-drafter.yaml. The configuration looks for labels on the pull request to determine the type of change for the release changelog (enhancement, bug, chore) and which portion of the version number to increment (major, minor, patch).

Publish assets (publish-assets.yaml)

This workflow runs when a new release is published (either manually or via an automated process).

on:
  release:
    types:
      - published

When a release is created, the module is checked out and the metadata is built and validated. If the metadata is checks out then it is published to the gh-pages branch as index.yaml

Notify (notify.yaml)

This workflow runs when a new release is published (either manually or via an automated process).

on:
  release:
    types:
      - published

When a release is created, a repository dispatch is sent out to the repositories listed in the strategy.matrix.repo variable. By default, the automation-modules and ibm-garage-iteration-zero repositories are notified. When those modules receive the notification, an automation workflow is triggered on their end to deal with the newly available module version.

Module metadata

The module metadata adds extra descriptive information about the module that is used to build out the module catalog.

name: ""
type: terraform
description: ""
tags:
  - tools
  - devops
versions:
  - platforms: []
    #  providers:
    #    - name: ibm
    #      source: "ibm-cloud/ibm"
    dependencies: []
    #    - id: cluster
    #      refs:
    #        - source: github.com/ibm-garage-cloud/terraform-ibm-container-platform
    #          version: ">= 1.7.0"
    #        - source: github.com/ibm-garage-cloud/terraform-k8s-ocp-cluster
    #          version: ">= 2.0.0"
    #    - id: namespace
    #      refs:
    #        - source: github.com/ibm-garage-cloud/terraform-k8s-namespace
    #          version: ">= 2.1.0"
    variables: []
#    - name: cluster_type
#      moduleRef:
#        id: cluster
#        output: type_code
#    - name: cluster_ingress_hostname
#      moduleRef:
#        id: cluster
#        output: ingress_hostname
#    - name: cluster_config_file
#      moduleRef:
#        id: cluster
#        output: config_file_path
#    - name: tls_secret_name
#      moduleRef:
#        id: cluster
#        output: tls_secret_name
#    - name: releases_namespace
#      moduleRef:
#        id: namespace
#        output: name
#        discriminator: tools

• name - The name field is required and must be unique among the other modules. This value is used to reference the module in the Bill of Materials.
• description - The description should provide a summary of what the module does.
• tags - The tags are used to provide searchable keywords related to the module.
• versions - When the final module metadata is generated, the versions array will contain a different entry for each version with a snapshot of the inputs and outputs for that version. In the module.yaml file this array should contain a single entry that describes the current version's dependencies and inputs.
• versions[*].providers - Terraform providers used by the module. Required if the ibm terraform provider is used
• versions[*].dependencies - The external modules upon which this module depends. These dependencies are used to offload logic for which this module should not be responsible and retrieve the necessary values from the outputs of these dependencies. Additionally, this allows resources to be shared between modules by referencing to the same external dependency instance.
• versions[*].variables - Additional metadata provided for the input variables. When the metadata is generated for the release, the information for all the input variables is read from variables.tf and is supplemented with the information provided here. If there is no additional information to add to a variable it can be excluded from module.yaml. Examples of variable metadata that can be added: mapping the variable to the output of a dependency or setting the scope of the variable to global, ignore, or module (the default).

Module test logic

The test/stages folder contains the terraform template needed to execute the module. By convention, each module is defined in its own file. Also by convention, all prereqs or dependencies for the module are named stage1-xxx and the module to be tested is named stage2-xxx. This test logic will run every time a change is made to the repository to ensure there are no regressions to the module.

Submitting changes

1. Fork the module git repository into your personal org
2. In your forked repository, add the following secrets (note: if you are working in the repo in the Cloud Native Toolkit, these secrets are already available):

• IBMCLOUD_API_KEY - an API Key to an IBM Cloud account where you can provision the test instances of any resources you need

3. Create a branch in the forked repository where you will do your work
4. Create a draft pull request in the Cloud Native Toolkit repository for your branch as soon as you push your first change. Add labels to the pull request for the type of change (enhancement, bug, chore) and the type of release (major, minor, patch) to impact the generated release documentation.
5. When the changes are completed and the automated checks are running successfully, mark the pull request as "Ready to review".
6. The module changes will be reviewed and the pull request merged. After the changes are merged, the automation in the repo create a new release of the module.

Development

Adding logic and updating the test

1. Start by implementing the logic in main.tf, adding required variables to variables.tf as necessary.
2. Update the test/stages/stage2-xxx.tf file with any of the required variables.
3. If the module has dependencies on other modules, add them as test/stages/stage1-xxx.tf and reference the output variables as variable inputs.
4. Review the validation logic in .github/scripts/validate-deploy.sh and update as appropriate.
5. Push the changes to the remote branch and review the check(s) on the pull request. If the checks fail, review the log and make the necessary adjustments.