terraform

name: terraform description: This skill should be used when writing or reviewing Terraform code, or when the project uses "Terraform", "HCL", "tfvars", "aws_iam_role", "data sources", or infrastructure-as-code patterns. Provides Terraform coding conventions, patterns, and best practices. Project-specific conventions always take priority. version: 0.1.0

Terraform Conventions

Coding conventions and best practices for Terraform projects. Project-specific conventions (CLAUDE.md, style guides) always take priority over this guidance.

General Conventions

• Prefer data sources over hardcoded values (e.g., data.aws_region.current, data.aws_caller_identity.current)
• Use locals for computed values and merging configuration
• Use jsonencode to compose JSON objects instead of raw string literals

Resource Naming

• Use snake_case for all resource names and variables, with exceptions:
  • Resource name in Terraform should match the actual resource name in the provider (e.g., when name = "FooBar", use resource "..." "FooBar")
• IAM role and policy names use PascalCase (e.g., Ec2Bastion, EcsApp)
• Use hyphenated lowercase for resource identifiers (e.g., ec2-default, dns-cache)

File Organization

Standard file structure per Terraform directory:

• aws.tf — AWS provider configuration with standard data sources (data.aws_region.current, data.aws_caller_identity.current, data.aws_default_tags.current)
• backend.tf — S3 backend configuration
• versions.tf — Provider version constraints
• Resource-specific files: vpc.tf, sg.tf, route53.tf, iam.tf, etc.
• Multiple IAM files when needed: iam_lambda.tf, iam_states.tf, iam_ec2_default.tf
• outputs.tf — Output definitions (when needed)
• locals.tf — Local values (when needed)

Variable Definitions

• Always specify type for variables
• Use default = {} for optional map variables
• Group related variables together with blank lines

Resource Arguments

• Multi-line arguments consistently formatted
• Use trailing commas in lists
• Align equals signs for readability in blocks

AWS-Specific

• Use data.aws_iam_policy_document whenever possible instead of jsonencode
• Use AWS managed policies via data.aws_iam_policy when available

Tags and Metadata

• Use default_tags at provider level for Project and Component tags
• Include meaningful resource-specific tags when needed

IAM Roles (aws_iam_role)

• Trust policies use separate data.aws_iam_policy_document with -trust suffix
• Split policies into multiple documents when they get large
• Use specific resource ARNs; avoid wildcards where possible
• Role names use PascalCase (e.g., NetKea, NwEc2Default)
• Include descriptive description field referencing the Terraform path

IAM Instance Profiles (aws_iam_instance_profile)

• Name should match the associated IAM role name
• Use aws_iam_role.Role.name for both name and role attributes