[Terraform] 입력 변수 (Input Variable)

✔️ 입력 변수 (Input Variable)

Input Variables - Configuration Language | Terraform by HashiCorp

Terraform에서의 변수는 Input Variable이다. 

변수는 variable이라는 블록을 사용하며 " " 안에 변수명을 지정한다.
변수를 정의할 때 몇가지 속성이 있다.

• description - 변수에 대한 설명
• type - 변수의 값으로 들어갈 수 있는 타입
• default - 변수의 기본값

main.tf 파일에 변수를 선언해도 되지만 ansible에서 기능을 분리시켰던 것처럼
variables.tf 라는 파일을 만들어서 유지보수 하기 쉽게 만드는 것이 좋다.

 

변수 선언 예시

variable "instance_name" { 
  description = "Value of the Name tag for the EC2 instance" 
  type = string 
  default = "ExampleAppServerInstance" 
}

 

변수 사용 예시

 resource "aws_instance" "app_server" {
   ami           = "ami-08d70e59c07c61a3a"
   instance_type = "t2.micro"

   tags = {
-    Name = "ExampleAppServerInstance"
+    Name = var.instance_name # 변수를 참조할 때는 "" 을 사용하면 안된다.
   }                          # 값이 그대로 들어가기 때문이다. 
 }

다른 예시를 하나 더 보자

variable "image_id" {
  type = string
}

variable "availability_zone_names" {
  type    = list(string)
  default = ["us-west-1a"]
}

예시를 보면 variable 블록에는 default 값이 없을 수도 있다. 
즉, 이 블록은 변수를 정의하기 위해 선언하는 것이지 값을 정의하기 위한 것이 아니다. 
값을 할당하기 위해서는 변수 값 할당 방법을 이용한다.

 

✔️Arguments

Terraform CLI는 변수 선언에 대해 다음과 같은 선택적 인수를 정의한다.

• default - 이 변수에 기본적으로 설정할 값
• type - value의 타입
• description - 설명
• validation - 부여한 value 값을 검증하는 코드
• sensitive - terraform show에서 출력 여부 (default는 출력이다.)
• nullable - 변수가 모듈내에서 null일 수 있는지의 여부를 지정

일반적으로는 type, default, description을 설정하고 나머지 인자는 부가적인 것이다.

• type
  • 일반 타입
    • string
      • "app_server"
    • number
      • 1
      • 1.0
    • bool
      • true
      • false
  • 복합 타입
    • list / tuple
      • [a, b, c]
    • map / object → list + dictionary
      • {a = abc, b = xyz}

variables abc {
type = list(string)
# ["a", "b"]
type = list(number)
# [1, 2]
}

• default : 기본 값
• description : 설명

배운 내용을 적용시켜보자

코드를 기능적으로 나누면 main.tf, provider.tf, variable.tf 세개의 파일로 분리할 수 있다.
main.tf

resource "aws_instance" "app_server" {
  ami           = "ami-0454bb2fefc7de534"
  instance_type = "t2.micro"

  tags = {
    Name        = var.instance_name
    Environment = "Terraform"
  }

  depends_on = [
    aws_s3_bucket.app_bucket,
  ]

}

# Elastic IP resource
resource "aws_eip" "app_server_eip" {
  instance = aws_instance.app_server.id
  vpc      = true
}


# S3 Bucket
resource "aws_s3_bucket" "app_bucket" {
  bucket = "ssh-20220421"
}

provider.tf

variable "instance_name" {
  type        = string
  description = "Instance Name"
  default     = "App Instance"
}

variable.tf

terraform {
  required_providers {
    aws = {
      source  = "hashicorp/aws"
      version = "~> 3.27"
    }
  }
  required_version = ">= 0.14.9"
}

provider "aws" {
  profile = "default"
  region  = "ap-northeast-2"
}

잘 실행된다.

[vagrant@controller 01]$ terraform plan

Terraform used the selected providers to generate the following execution plan. Resource actions are indicated with the following symbols:
  + create

Terraform will perform the following actions:

  # aws_eip.app_server_eip will be created
  + resource "aws_eip" "app_server_eip" {
      + allocation_id        = (known after apply)
      + association_id       = (known after apply)
      + carrier_ip           = (known after apply)
      + customer_owned_ip    = (known after apply)
      + domain               = (known after apply)
      + id                   = (known after apply)
      + instance             = (known after apply)
      + network_border_group = (known after apply)
      + network_interface    = (known after apply)
      + private_dns          = (known after apply)
      + private_ip           = (known after apply)
      + public_dns           = (known after apply)
      + public_ip            = (known after apply)
      + public_ipv4_pool     = (known after apply)
      + tags_all             = (known after apply)
      + vpc                  = true
    }

  # aws_instance.app_server will be created
  + resource "aws_instance" "app_server" {
      + ami                                  = "ami-0454bb2fefc7de534"
      + arn                                  = (known after apply)
      + associate_public_ip_address          = (known after apply)
      + availability_zone                    = (known after apply)
      + cpu_core_count                       = (known after apply)
      + cpu_threads_per_core                 = (known after apply)
      + disable_api_termination              = (known after apply)
      + ebs_optimized                        = (known after apply)
      + get_password_data                    = false
      + host_id                              = (known after apply)
      + id                                   = (known after apply)
      + instance_initiated_shutdown_behavior = (known after apply)
      + instance_state                       = (known after apply)
      + instance_type                        = "t2.micro"
      + ipv6_address_count                   = (known after apply)
      + ipv6_addresses                       = (known after apply)
      + key_name                             = (known after apply)
      + monitoring                           = (known after apply)
      + outpost_arn                          = (known after apply)
      + password_data                        = (known after apply)
      + placement_group                      = (known after apply)
      + placement_partition_number           = (known after apply)
      + primary_network_interface_id         = (known after apply)
      + private_dns                          = (known after apply)
      + private_ip                           = (known after apply)
      + public_dns                           = (known after apply)
      + public_ip                            = (known after apply)
      + secondary_private_ips                = (known after apply)
      + security_groups                      = (known after apply)
      + source_dest_check                    = true
      + subnet_id                            = (known after apply)
      + tags                                 = {
          + "Environment" = "Terraform"
          + "Name"        = "App Instance"
        }
      + tags_all                             = {
          + "Environment" = "Terraform"
          + "Name"        = "App Instance"
        }
      + tenancy                              = (known after apply)
      + user_data                            = (known after apply)
      + user_data_base64                     = (known after apply)
      + vpc_security_group_ids               = (known after apply)

      + capacity_reservation_specification {
          + capacity_reservation_preference = (known after apply)

          + capacity_reservation_target {
              + capacity_reservation_id = (known after apply)
            }
        }

      + ebs_block_device {
          + delete_on_termination = (known after apply)
          + device_name           = (known after apply)
          + encrypted             = (known after apply)
          + iops                  = (known after apply)
          + kms_key_id            = (known after apply)
          + snapshot_id           = (known after apply)
          + tags                  = (known after apply)
          + throughput            = (known after apply)
          + volume_id             = (known after apply)
          + volume_size           = (known after apply)
          + volume_type           = (known after apply)
        }

      + enclave_options {
          + enabled = (known after apply)
        }

      + ephemeral_block_device {
          + device_name  = (known after apply)
          + no_device    = (known after apply)
          + virtual_name = (known after apply)
        }

      + metadata_options {
          + http_endpoint               = (known after apply)
          + http_put_response_hop_limit = (known after apply)
          + http_tokens                 = (known after apply)
          + instance_metadata_tags      = (known after apply)
        }

      + network_interface {
          + delete_on_termination = (known after apply)
          + device_index          = (known after apply)
          + network_interface_id  = (known after apply)
        }

      + root_block_device {
          + delete_on_termination = (known after apply)
          + device_name           = (known after apply)
          + encrypted             = (known after apply)
          + iops                  = (known after apply)
          + kms_key_id            = (known after apply)
          + tags                  = (known after apply)
          + throughput            = (known after apply)
          + volume_id             = (known after apply)
          + volume_size           = (known after apply)
          + volume_type           = (known after apply)
        }
    }

  # aws_s3_bucket.app_bucket will be created
  + resource "aws_s3_bucket" "app_bucket" {
      + acceleration_status         = (known after apply)
      + acl                         = "private"
      + arn                         = (known after apply)
      + bucket                      = "ssh-20220421"
      + bucket_domain_name          = (known after apply)
      + bucket_regional_domain_name = (known after apply)
      + force_destroy               = false
      + hosted_zone_id              = (known after apply)
      + id                          = (known after apply)
      + object_lock_enabled         = (known after apply)
      + region                      = (known after apply)
      + request_payer               = (known after apply)
      + tags_all                    = (known after apply)
      + website_domain              = (known after apply)
      + website_endpoint            = (known after apply)

      + object_lock_configuration {
          + object_lock_enabled = (known after apply)

          + rule {
              + default_retention {
                  + days  = (known after apply)
                  + mode  = (known after apply)
                  + years = (known after apply)
                }
            }
        }

      + versioning {
          + enabled    = (known after apply)
          + mfa_delete = (known after apply)
        }
    }

Plan: 3 to add, 0 to change, 0 to destroy.

 

✔️ 변수 값 할당

✔️ -var 옵션

variable.tf 의 default 값을 지우고 태그 정보를 확인하면 태그의 Name이 xyz로 출력된다.

[vagrant@controller 01]$ terraform plan -var "instance_name=xyz"
 + tags                                 = {
          + "Environment" = "Terraform"
          + "Name"        = "xyz"
        }
      + tags_all                             = {
          + "Environment" = "Terraform"
          + "Name"        = "xyz"
        }

하지만 variable.tf 에서 default가 있어도 해당 명령을 실행하면

[vagrant@controller 01]$ terraform plan -var "instance_name=xyz"

default = "App Instance" 값은 무시되며 xyz가 출력된다.

정리하자면 변수 파일에 선언된 변수보다 -var 옵션의 우선순위가 더 높다.

 

✔️ terraform.tfvars 파일

Terraform에서 -var 옵션보다는 terraform.tfvars 파일을 자주 사용한다.

[vagrant@controller 01]$ code terraform.tfvars
[vagrant@controller 01]$ cat terraform.tfvars
instance_name = "xyz123"

+ tags                                 = {
          + "Environment" = "Terraform"
          + "Name"        = "xyz123"
        }
      + tags_all                             = {
          + "Environment" = "Terraform"
          + "Name"        = "xyz123"
        }