[Bug]: Establishing the default value in the `backup_window` property does not work

[zucchinidev]

Terraform Core Version

1.3.1

AWS Provider Version

4.33.0

Affected Resource(s)

• aws_db_instance
  • backup_window

Expected Behavior

Establishing a null value in the backup_window property configures the backup window with the default value associated with the region.

When creating a database with automated backups enabled, that is to say, setting the backup_retention_period property with a value between 0 and 35, AWS establish a default backup_window value depending on the region if the value is unset. See https://docs.aws.amazon.com/AmazonRDS/latest/UserGuide/USER_WorkingWithAutomatedBackups.html#USER_WorkingWithAutomatedBackups.BackupWindow. Once we set this value and we want to return to the default value, that is to say, setting the null value, the backup window must be associated with the default values related to the region.

Actual Behavior

Establishing a null value in the backup_window property does not work.

When creating a database with automated backups enabled, that is to say, setting the backup_retention_period property with a value between 0 and 35, AWS establish a default backup_window value depending on the region if the value is unset. See https://docs.aws.amazon.com/AmazonRDS/latest/UserGuide/USER_WorkingWithAutomatedBackups.html#USER_WorkingWithAutomatedBackups.BackupWindow. Once we set this value and we want to return to the default value, that is to say, setting the null value, the operation has no effect, and the previously set value continues as the value selected in the console.

Several tests were realised, as well as some initial analysis:

• A null value was passed after selecting a valid backup window. The null value is not reflected when executing Terraform plan command.
• Analyzed AWS documentation where it could be observed that the default value is only mentioned when it comes to creating the database and never in the updating.
• Analyzed the AWS API documentation where it could be observed that the API admits the value in both, creating and updating operations.

Relevant Error/Panic Output Snippet

No response

Terraform Configuration Files

resource "random_string" "username" {
  length  = 16
  special = false
  numeric = false
}

resource "random_password" "password" {
  length           = 32
  special          = false
  // https://docs.aws.amazon.com/AmazonRDS/latest/UserGuide/CHAP_Limits.html#RDS_Limits.Constraints
  override_special = "~_-."
}

resource "aws_db_instance" "db_instance" {
  skip_final_snapshot     = true
  engine                  = "mysql"
  engine_version          = "8.0"
  instance_class          = "db.t2.small"
  db_name                 = "testazucgar"
  allocated_storage       = 100
  username                = random_string.username.result
  password                = random_password.password.result
  apply_immediately       = true
  storage_encrypted       = false
  deletion_protection     = false
  backup_retention_period = 2
  backup_window           = "18:00-18:30"
#  backup_window           = null
}

provider "aws" {
  region     = "us-west-2"
  access_key = "XXXXXXXXXXXXXXX"
  secret_key = "XXXXXXXXXXXXXXX"
}

terraform {
  required_providers {
    aws = {
      source  = "hashicorp/aws"
      version = ">= 4.0"
    }
    random = {
      source  = "hashicorp/random"
      version = ">= 3.3.2"
    }
  }
}

Steps to Reproduce

• Terraform apply to create the database,
• Check default value in backup_window AWS console.
• Set backup_window = null and execute Terraform plan
  • Modification is not detected
  • Terraform apply
    • Database is not modified.

Debug Output

No response

Panic Output

No response

Important Factoids

No response

References

No response

Would you like to implement a fix?

No response

[github-actions[bot]]

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[github-actions[bot]]

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