Fix Terraform Error: Invalid Type Specification

# ❌ Don't quote type names
variable "name" {
  type = "string"     # Wrong — quotes make it a string literal
}
 
# ✅ Types are keywords, not strings
variable "name" {
  type = string
}

Error: Invalid type specification
 
  on variables.tf line 2, in variable "name":
   2:   type = "string"
 
A type specification is either a primitive type keyword (bool, number,
string) or a complex type constructor call, like list(string).

variable "name"    { type = string }   # "hello"
variable "count"   { type = number }   # 42, 3.14
variable "enabled" { type = bool }     # true, false

variable "names" { type = list(string) }
# ["web", "api", "db"]
 
variable "ports" { type = list(number) }
# [80, 443, 8080]
 
variable "tags" { type = map(string) }
# { Environment = "prod", Team = "platform" }
 
variable "unique_ids" { type = set(string) }
# ["a", "b", "c"] — duplicates removed

# Object — fixed keys with types
variable "database" {
  type = object({
    engine         = string
    instance_class = string
    port           = number
    multi_az       = bool
  })
}
 
# Tuple — fixed-length list with typed positions
variable "config" {
  type = tuple([string, number, bool])
  # ["web", 8080, true]
}

variable "ingress_rules" {
  type = list(object({
    port        = number
    protocol    = string
    cidr_blocks = list(string)
  }))
}
 
variable "environment_tags" {
  type = map(map(string))
  # { prod = { owner = "ops" }, dev = { owner = "dev" } }
}

variable "instance" {
  type = object({
    name          = string
    instance_type = string
    monitoring    = optional(bool, false)       # Default: false
    tags          = optional(map(string), {})   # Default: {}
    ebs_size      = optional(number)            # Default: null
  })
}

variable "flexible" {
  type = any    # Accepts anything — use sparingly
}
 
variable "mixed_list" {
  type = list(any)    # List of anything
}