---
tags: 'Infrastructure as Code'
---
# Terraform conventions

## Naming Rules
### General conventions
- 使用4個空格
- 使用小寫字母或是數字
- 使用底線(_)分隔單詞

### Resource and data source arguments
- 請使用單數名詞作為名稱
- O:

        resource "azurerm_resource_group" "example" {}

- X:

        resource "azurerm_resource_group" "examples" {}

- 不在資源名稱中重複資源類型
- O:

        resource "azurerm_resource_group" "example" {}

- X:

        resource "azurerm_resource_group" "example_resource_group" {}

- 當使用多個argument, 請對齊其等號
- O:

        resource "azurerm_virtual_network" "vnet" {
            name                = var.vnet_name
            resource_group_name = data.azurerm_resource_group.network.name
            location            = data.azurerm_resource_group.network.location
            address_space       = [var.address_space]
            dns_servers         = var.dns_servers
      
            tags                = var.tags
        }

- X:

        resource "azurerm_virtual_network" "vnet" {
            name = var.vnet_name
            resource_group_name = data.azurerm_resource_group.network.name
            location = data.azurerm_resource_group.network.location
            address_space = [var.address_space]
            dns_servers = var.dns_servers
      
            tags = var.tags
        }

- 當argument和block出現在同一層級時, 請將所有argument放在頂部, 並用空行分隔argument與block
- O:

        resource "azurerm_virtual_network" "vnet" {
            name                = var.vnet_name
            resource_group_name = data.azurerm_resource_group.network.name
            location            = data.azurerm_resource_group.network.location
            address_space       = [var.address_space]
            dns_servers         = var.dns_servers
      
            tags                = var.tags
      
            lifecycle {
                create_before_destroy = true
            }
        }

- 請將count放置在第一行, 並空格一行
- O:

        resource "azurerm_storage_account" "vm-sa" {
            count                    = var.boot_diagnostics ? 1 : 0
            
            name                     = "bootdiag${lower(random_id.vm-sa.hex)}"
            resource_group_name      = data.azurerm_resource_group.vm.name
            location                 = coalesce(var.location, data.azurerm_resource_group.vm.location)
            account_tier             = element(split("_", var.boot_diagnostics_sa_type), 0)
            account_replication_type = element(split("_", var.boot_diagnostics_sa_type), 1)
  
            tags                     = var.tags
        }

- X:

        resource "azurerm_storage_account" "vm-sa" {          
            name                     = "bootdiag${lower(random_id.vm-sa.hex)}"
            resource_group_name      = data.azurerm_resource_group.vm.name
            location                 = coalesce(var.location, data.azurerm_resource_group.vm.location)
            account_tier             = element(split("_", var.boot_diagnostics_sa_type), 0)
            account_replication_type = element(split("_", var.boot_diagnostics_sa_type), 1)
            
            count                    = var.boot_diagnostics ? 1 : 0
  
            tags                     = var.tags
        }

### Module

#### When to write a module
- 如果有多個資源會一起被使用到
- 不建議編寫僅作為單個資源類型

#### Structure

minimal-module
    ├── README.md
    ├── main.tf
    ├── outputs.tf
    └── variables.tf

#### Variables
- 變數中的參數順序為: description > type > default

    variable "cidr_block" {
        description = "The CIDR block for AWS VPC"
        type        = string
        default     = "10.0.0.0/16"
    }

- 使用與資源相同的變數名
- 即使你認為很簡單, 請描述每個變數

#### Outputs
- 輸出名稱結構: <name>_<type>_<attribute>
- 盡可能提供output變數
- 即使你認為很簡單, 請描述每個輸出
- 如果輸出是一個list, 請使用複數名稱

## Structure

- 共用資源，如provider, backend, resource_group等等放入main.tf
- 共用資源變數放入bootstrap.tfvars(不可放入密碼等等資訊, 請善用環境變數)
- 根據[資源類型](https://www.terraform.io/docs/providers/azurerm/index.html)新增或放入對應的<resource_type>.tf中

example_project

├── bootstrap.tfvars
├── compute.local.tf
├── compute.tf
├── main.tf
├── main.variables.tf
├── modules
│   └── virtual_network
│       ├── main.tf
│       ├── outputs.tf
│       └── variables.tf
├── network.local.tf
├── network.tf
├── README.md
└── tags.tf