Terraform variable validation

variables.tf

# Using anytrue()

variable "instance_size" {
  type        = string
  description = "RDS Instance Size"

  validation {
    condition = anytrue([
      var.instance_size == "db.t3.micro",
      var.instance_size == "db.t3.small",
      var.instance_size == "db.t3.medium"
    ])
    error_message = "Instance size does not match db.t3.micro, db.t3.small or db.t3.medium."
  }
}

# Using contains()

variable "bucket_acl" {
  type        = string
  description = "ACL to be set on S3 bucket"

  validation {
    condition     = contains(["private", "public-read", "authenticated-read"], var.bucket_acl)
    error_message = "S3 bucket ACL must be 'private', 'public-read' or 'authenticated-read'."
  } 
}