Terraform Style Guide

Table of Contents

• Introduction
• Syntax
  • Spacing
  • Resource Block Alignment
  • Comments
• Naming Conventions
  • File Names
  • Parameter, Meta-parameter and Variable Naming
  • Resource Naming

Introduction

This repository gives coding conventions for Terraform's HashiCorp Configuration Language (HCL). Terraform allows infrastructure to be described as code. As such, we should adhere to a style guide to ensure readable and high quality code.

Syntax

• Strings are in double-quotes.

Spacing

Use 2 spaces when defining resources except when defining inline policies or other inline resources.

resource "aws_iam_role" "iam_role" {
  name = "${var.resource_name}-role"
  assume_role_policy = <<EOF
{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Action": "sts:AssumeRole",
      "Principal": {
        "Service": "ec2.amazonaws.com"
      },
      "Effect": "Allow",
      "Sid": ""
    }
  ]
}
EOF
}

Resource Block Alignment

Parameter definitions in a resource block should be aligned. The terraform fmt command can do this for you.

provider "aws" {
  access_key = "${var.aws_access_key}"
  secret_key = "${var.aws_secret_key}"
  region     = "us-east-1"
}

Variables

Variables should be put into alphabetical order

Comments

When commenting use "#" and a space in front of the comment for a single line comment.

# CREATE ELK IAM ROLE 
...

and "/* */" for a multi-line comment.

/* variable "environment" {
  default = "dev"
} */

Naming Conventions

File Names

Create a separate resource file for each type of AWS resource. Similar resources should be defined in the same file and named accordingly.

ami.tf
autoscaling_group.tf
cloudwatch.tf
iam.tf
launch_configuration.tf
providers.tf
s3.tf
security_groups.tf
sns.tf
sqs.tf
user_data.sh
variables.tf

Parameter, Meta-parameter and Variable Naming

Only use an underscore (_) when naming Terraform resources like TYPE/NAME parameters and variables.

resource "aws_security_group" "security_group" {
...

Resource Naming

Only use a hyphen (-) when naming the component being created.

resource "aws_security_group" "security_group" {
 name = "${var.resource_name}-security-group"
...