Terraform modules are reusable, self-contained units of infrastructure code that allow users to encapsulate and organize resources in an efficient and scalable process. By grouping related resources into a module, engineering teams enable project teams to manage complex infrastructure setups with ease. These modules can be shared and versioned, promoting consistency and reducing redundancy across different environments.
In this note, I’ll help you understand a few key factors and considerations as you guide your organization through the adoption of Terraform modules.
Adopting a Terraform module-based development approach enables cloud engineers to work efficiently and innovate without compromising on crucial aspects, such as security and cost management. By using modules, teams can enforce guardrails that ensure infrastructure deployments are secure, cost-effective, and aligned with best practices.
Before starting Terraform module development, teams must grasp the fundamental concepts of Terraform modules. To establish a solid foundation, refer to the official Terraform Modules Documentation on HashiCorp’s website. This tutorial provides a comprehensive guide on how to create and use modules effectively, ensuring that the infrastructure is consistent, secure, and scalable.
I have worked with nearly a dozen organizations on their Terraform module development journeys, and based on my experience, I’ve observed several traits that contribute to a successful Terraform module adoption. These can be broadly classified into:
Collaboration and Management
Module Design and Architecture
Version Control and Repository Management
Quality and Best Practices
Performance, Cost, and Usability Considerations
Now that we’ve established the importance of Terraform modules and their broad classifications, let’s dive into the crucial considerations you should keep in mind while designing them.
#1 – Build Organizational Consensus ( Collaboration and Management)
Before writing a Terraform module, discuss the idea and its benefits with the organization. Eventually, it’s the organization that will use the module, so we want to hear their thoughts and, at the same time communicate that these modules are not to restrict what they are currently doing, but to aid them with the experience of others in the organization, so that their projects are built securely and efficiently, right from the beginning.
#2 – Module Scope Definition ( Module Design and Architecture)
Since these modules are designed for the project team to consume, a good starting point would be to allow them to identify the most common cloud use cases across the organization to convert into modules.
#3 – Use-Case Driven Development ( Module Design and Architecture)
Design modules around specific use cases rather than individual resources. This approach ensures modules solve real business problems and provide complete solutions. Consider the end-user’s perspective and common deployment patterns when designing module functionality to ensure optimal usability.
#4 – Automate Documentation with terraform-docs ( Quality and Best Practices)
Documentation is a crucial aspect of module development, and manual maintenance can be time-consuming and error-prone. Terraform-docs automatically generates comprehensive documentation by analyzing your Terraform code, including inputs, outputs, providers, and requirements. This tool ensures that documentation stays current with code changes and maintains consistency across all modules. Please check automate-terraform-modules-readme-generation for more information.
#5 – Maintain Example Code Repository ( Performance, Usage, and Cost Considerations)
Including an examples directory in your module repository is essential for demonstrating proper usage patterns. These examples serve as both documentation and working templates that users can reference or use as a basis for their work. Well-documented examples significantly reduce the learning curve and help prevent common implementation mistakes.
#6 – Version Control ( Version Control and Repository Management)
Store modules in a version control system, such as GitHub, to track changes, manage collaborations, and maintain a history. This provides a central location for code review, issue tracking, and release management. GitHub’s features, such as pull requests and actions (workflows), can enhance the development workflow.
#7 – Version Tagging Strategy ( Version Control and Repository Management)
Proper version tagging helps users identify and lock to specific module versions. Use semantic versioning (major.minor.patch) to communicate the nature of changes. This practice ensures stability and predictability for module consumers.
#8 – Security and Coding Standards ( Quality and Best Practices)
Adhere to coding standards and security best practices in module development. Utilize Checkov/Sentinel policies to design secure modules based on organization policies and industry best practices. This includes proper resource naming, tag management, and security configurations. Regular code reviews and security assessments should be part of the development process.
#9 – Test Case Implementation ( Quality and Best Practices)
Develop comprehensive test cases to validate module functionality utilizing the Terraform test framework. Testing builds confidence in the module’s reliability and helps catch issues early. Include both unit tests (variable validation) and integration tests where applicable. Please check automate-terraform-testing for more information.
#10 – Regular Team Sync-ups ( Collaboration and Management)
Regular weekly meetings (office hours) with organizational members help maintain alignment and address challenges promptly. These sync-ups could also be used for project teams to share module adoption success stories and key learnings.
#11 – Issue Tracking Implementation ( Collaboration and Management)
Utilize GitHub issues or similar systems to track module enhancements and bugs. This insight provides transparency and helps prioritize development efforts. It also creates a searchable history of decisions and changes.
#12 – Single Module Per Repository ( Version Control and Repository Management)
Maintaining separate repositories for each module improves version control and reduces complexity. This approach facilitates easier management of dependencies, tracking of issues, and maintenance of documentation. It also allows for independent versioning and release cycles.
#13 – Two-Level Module Nesting Limit ( Module Design and Architecture)
Restrict module nesting to a maximum of two levels to maintain code clarity and prevent complex dependencies. Deep nesting can lead to difficult troubleshooting and maintenance issues. This limitation helps keep the module structure manageable and understandable.
#14 – Comprehensive Output Definition ( Module Design and Architecture)
Define clear and practical outputs that downstream consumers can reference. Well-designed outputs make modules more versatile and easier to integrate with other resources. Consider what information users might need for their configurations.
#15 – Collaborative Development Model ( Collaboration and Management)
Encourage participation from project teams in the development of modules. This collaborative development model creates a sense of ownership and helps ensure modules meet real-world needs. Set up clear contribution guidelines and review processes.
#16 – Resource Cost Estimation ( Performance, Usage, and Cost Considerations)
Include cost estimates for typical deployment scenarios in the module documentation. Use the example configurations to provide realistic cost projections. These estimates enable teams to plan budgets and make informed decisions about resource allocation. Please check estimate-cloud-resource-cost for more information.
#17 – Deployment Duration Documentation ( Performance, Usage, and Cost Considerations)
Document the desired provisioning duration for resources created by the module. This information helps teams plan their deployment schedules and set appropriate expectations. Include factors that affect deployment duration, such as the time it takes for a property value in a resource to be updated in the case of a re-deploy.
Organizations today are increasingly turning to Terraform modules because they offer a scalable and secure approach to infrastructure management. Modules empower developers with the flexibility to creatively provision solutions using Terraform, all while adhering to organizational standards and best practices.
Focusing on these 17 key considerations will help your organization embark on a journey that will enable a culture that fosters learning from within. Such behavior not only increases developer productivity but also enhances team cohesion as learning and sharing become ingrained in the organization’s culture.
Last but not least, I’d want to leave you with one of the best talks on Terraform Module development. A few months ago, I was at Boston for HashiConf 2024 where I attending a fantastic talk featuring Terraform experts – Ned, Bruno, and Drew on how to design Terraform modules.
My Devops Journal 