How to rotate random passwords in Terraform

This is a pattern to use when creating passwords in Terraform.  The below pattern accomplishes the following objectives.

• Passwords are not stored in the tf files, which in turn means they are not stored in Git.
• Easily rotate the password by changing the password_change_id variable.
• Generate secure random passwords.

variable "password_change_id" {
  type        = string
  default     = "1970-01-01"
  description = "Id to trigger changing the master password"
}

resource "random_password" "adminpassword" {
  for_each = toset([var.password_change_id])
  length   = 32
  special  = false
}

locals {
  password = random_password.adminpassword[var.password_change_id].result
}

resource "aws_rds_cluster" "default" {
// lots of attributes are missing
  master_password = local.password
}

output "password" {
  sensitive = true
  value     = local.password
}

You can automate the change in your pipeline by using the Terraform Environment Variables. For example, the following commands will rotate the password monthly.  

set -x TF_VAR_password_change_id (date +%Y-%m)
terraform apply

You can change how frequently you change the password based on the date command.

# monthly
date +%Y-%m
# weekly
date +%Y-week-%U
# daily
date +%Y-%m-%d