Terraform

Terraform Conventions

General Instructions

• Use Terraform to provision and manage infrastructure.
• Use version control for your Terraform configurations.

Security

• Always use the latest stable version of Terraform and its providers.
  • Regularly update your Terraform configurations to incorporate security patches and improvements.
• Store sensitive information in a secure manner, such as using AWS Secrets Manager or SSM Parameter Store.
  • Regularly rotate credentials and secrets.
  • Automate the rotation of secrets, where possible.
• Use AWS environment variables to reference values stored in AWS Secrets Manager or SSM Parameter Store.
  • This keeps sensitive values out of your Terraform state files.
• Never commit sensitive information such as AWS credentials, API keys, passwords, certificates, or Terraform state to version control.
  • Use .gitignore to exclude files containing sensitive information from version control.
• Always mark sensitive variables as sensitive = true in your Terraform configurations.
  • This prevents sensitive values from being displayed in the Terraform plan or apply output.
• Use IAM roles and policies to control access to resources.
  • Follow the principle of least privilege when assigning permissions.
• Use security groups and network ACLs to control network access to resources.
• Deploy resources in private subnets whenever possible.
  • Use public subnets only for resources that require direct internet access, such as load balancers or NAT gateways.
• Use encryption for sensitive data at rest and in transit.
  • Enable encryption for EBS volumes, S3 buckets, and RDS instances.
  • Use TLS for communication between services.
• Regularly review and audit your Terraform configurations for security vulnerabilities.
  • Use tools like trivy, tfsec, or checkov to scan your Terraform configurations for security issues.

Modularity

• Use separate projects for each major component of the infrastructure; this:
  • Reduces complexity
  • Makes it easier to manage and maintain configurations
  • Speeds up plan and apply operations
  • Allows for independent development and deployment of components
  • Reduces the risk of accidental changes to unrelated resources
• Use modules to avoid duplication of configurations.
  • Use modules to encapsulate related resources and configurations.
  • Use modules to simplify complex configurations and improve readability.
  • Avoid circular dependencies between modules.
  • Avoid unnecessary layers of abstraction; use modules only when they add value.
    • Avoid using modules for single resources; only use them for groups of related resources.
    • Avoid excessive nesting of modules; keep the module hierarchy shallow.
• Use output blocks to expose important information about your infrastructure.
  • Use outputs to provide information that is useful for other modules or for users of the configuration.
  • Avoid exposing sensitive information in outputs; mark outputs as sensitive = true if they contain sensitive data.

Maintainability

• Prioritize readability, clarity, and maintainability.
• Use comments to explain complex configurations and why certain design decisions were made.
• Write concise, efficient, and idiomatic configs that are easy to understand.
• Avoid using hard-coded values; use variables for configuration instead.
  • Set default values for variables, where appropriate.
• Use data sources to retrieve information about existing resources instead of requiring manual configuration.
  • This reduces the risk of errors, ensures that configurations are always up-to-date, and allows configurations to adapt to different environments.
  • Avoid using data sources for resources that are created within the same configuration; use outputs instead.
  • Avoid, or remove, unnecessary data sources; they slow down plan and apply operations.
• Use locals for values that are used multiple times to ensure consistency.

Style and Formatting

• Follow Terraform best practices for resource naming and organization.
  • Use descriptive names for resources, variables, and outputs.
  • Use consistent naming conventions across all configurations.
• Follow the Terraform Style Guide for formatting.
  • Use consistent indentation (2 spaces for each level).
• Group related resources together in the same file.
  • Use a consistent naming convention for resource groups (e.g., providers.tf, variables.tf, network.tf, ecs.tf, mariadb.tf).
• Place depends_on blocks at the very beginning of resource definitions to make dependency relationships clear.
  • Use depends_on only when necessary to avoid circular dependencies.
• Place for_each and count blocks at the beginning of resource definitions to clarify the resource's instantiation logic.
  • Use for_each for collections and count for numeric iterations.
  • Place them after depends_on blocks, if they are present.
• Place lifecycle blocks at the end of resource definitions.
• Alphabetize providers, variables, data sources, resources, and outputs within each file for easier navigation.
• Group related attributes together within blocks.
  • Place required attributes before optional ones, and comment each section accordingly.
  • Separate attribute sections with blank lines to improve readability.
  • Alphabetize attributes within each section for easier navigation.
• Use blank lines to separate logical sections of your configurations.
• Use terraform fmt to format your configurations automatically.
• Use terraform validate to check for syntax errors and ensure configurations are valid.
• Use tflint to check for style violations and ensure configurations follow best practices.
  • Run tflint regularly to catch style issues early in the development process.

Documentation

• Always include description and type attributes for variables and outputs.
  • Use clear and concise descriptions to explain the purpose of each variable and output.
  • Use appropriate types for variables (e.g., string, number, bool, list, map).
• Document your Terraform configurations using comments, where appropriate.
  • Use comments to explain the purpose of resources and variables.
  • Use comments to explain complex configurations or decisions.
  • Avoid redundant comments; comments should add value and clarity.
• Include a README.md file in each project to provide an overview of the project and its structure.
  • Include instructions for setting up and using the configurations.
• Use terraform-docs to generate documentation for your configurations automatically.

Testing

• Write tests to validate the functionality of your Terraform configurations.
  • Use the .tftest.hcl extension for test files.
  • Write tests to cover both positive and negative scenarios.
  • Ensure tests are idempotent and can be run multiple times without side effects.