Terraformのvariableにはvalidationがあり、入力値の条件を事前にチェックできます。
この記事では「10文字以内」という文字数制限にフォーカスして、validationの書き方と挙動を紹介します。
この記事でやること
- 10文字以内の制約を
validationで実装する - ルール違反時のエラー表示を確認する
validationの書き方
今回のポイントはこの3行です。
validation {
condition = length(var.bucket_name) <= 10
error_message = "bucket_name must be 10 characters or fewer."
}
何をしているか
-
condition: 真偽値を返す式を書く（今回は長さが10以下かどうか） -
error_message:conditionがfalseのときに表示されるメッセージ
このブロックがあるだけで、入力時点で文字数チェックが走ります。
サンプル構成
ファイル配置構成
.
├── main.tf
├── variables.tf
└── outputs.tf
main.tf
main.tf
terraform {
required_providers {
aws = {
source = "hashicorp/aws"
version = ">= 5.0"
}
}
}
provider "aws" {
region = var.aws_region
}
resource "aws_s3_bucket" "this" {
bucket = var.bucket_name
tags = var.tags
}
variables.tf（validationの実装例）
variables.tf
variable "aws_region" {
type = string
description = "AWS region."
default = "ap-northeast-1"
}
variable "bucket_name" {
type = string
description = "Name of the S3 bucket (max 10 characters)."
validation {
condition = length(var.bucket_name) <= 10
error_message = "bucket_name must be 10 characters or fewer."
}
}
variable "tags" {
type = map(string)
description = "Tags to apply to the bucket."
default = {}
}
outputs.tf
outputs.tf
output "bucket_id" {
value = aws_s3_bucket.this.id
description = "ID of the S3 bucket."
}
output "bucket_arn" {
value = aws_s3_bucket.this.arn
description = "ARN of the S3 bucket."
}
使い方（確認方法）
terraform
% terraform init
% terraform plan -var="bucket_name=example10"
実行結果（OK: 10文字以内）
OK
% terraform plan -var="bucket_name=example10"
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_s3_bucket.this will be created
+ resource "aws_s3_bucket" "this" {
+ acceleration_status = (known after apply)
+ acl = (known after apply)
+ arn = (known after apply)
+ bucket = "example10"
+ bucket_domain_name = (known after apply)
+ bucket_prefix = (known after apply)
+ bucket_region = (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)
+ policy = (known after apply)
+ region = "ap-northeast-1"
+ request_payer = (known after apply)
+ tags_all = (known after apply)
+ website_domain = (known after apply)
+ website_endpoint = (known after apply)
+ cors_rule (known after apply)
+ grant (known after apply)
+ lifecycle_rule (known after apply)
+ logging (known after apply)
+ object_lock_configuration (known after apply)
+ replication_configuration (known after apply)
+ server_side_encryption_configuration (known after apply)
+ versioning (known after apply)
+ website (known after apply)
}
Plan: 1 to add, 0 to change, 0 to destroy.
Changes to Outputs:
+ bucket_arn = (known after apply)
+ bucket_id = (known after apply)
Note: You didn't use the -out option to save this plan, so Terraform can't guarantee to take exactly these
actions if you run "terraform apply" now.
実行結果（NG: 10文字超）
NG
% terraform plan -var="bucket_name=too-long-name"
Planning failed. Terraform encountered an error while generating this plan.
╷
│ Error: Invalid value for variable
│
│ on variables.tf line 7:
│ 7: variable "bucket_name" {
│ ├────────────────
│ │ var.bucket_name is "too-long-name"
│
│ bucket_name must be 10 characters or fewer.
│
│ This was checked by the validation rule at variables.tf:11,3-13.
╵
上記のように10文字を超えると、validationのメッセージが表示されます。
補足
- 実際のS3バケット名の制約はもっと多いです（文字種や長さなど）。
- ここでは
validationの書き方に集中するため、あえてシンプルなルールにしています。
まとめ
validationを使うと、入力ミスを早い段階で発見できます。
まずは文字数制限のようなシンプルなルールから導入するのがおすすめです。