compatibility.md

Compatibility with Terraform

TFLint interprets the Terraform language with its own parser which is a fork of the Terraform's native one. This allows it to be parsed correctly even if Terraform is not installed at runtime.

The parser supports Terraform v1.x syntax and semantics. The language compatibility on Terraform v1.x is defined by Compatibility Promises. TFLint follows this promise. New features are only supported in newer TFLint versions, and bug and experimental features compatibility are not guaranteed.

The latest supported version is Terraform v1.9.

Input Variables

Like Terraform, TFLint supports the --var, --var-file options, environment variables (TF_VAR_*), and automatically loading variable definitions (terraform.tfvars and *.auto.tfvars) files. See Input Variables.

Input variables are evaluated just like in Terraform:

variable "instance_type" {
  default = "t2.micro"
}

resource "aws_instance" "foo" {
  instance_type = var.instance_type # => "t2.micro"
}

Unknown variables (e.g. no default) are ignored:

variable "instance_type" {}

resource "aws_instance" "foo" {
  instance_type = var.instance_type # => ignored
}

Sensitive variables are ignored. This is to avoid unintended disclosure.

variable "instance_type" {
  sensitive = true
  default   = "t2.micro"
}

resource "aws_instance" "foo" {
  instance_type = var.instance_type # => ignored
}

Local Values

TFLint supports Local Values.

variable "foo" {
  default = "variable value"
}

locals {
  static   = "static value"
  variable = var.foo
  local    = local.static
  resource = aws_instance.main.arn
}

local.static   # => "static value"
local.variable # => "variable value"
local.local    # => "static value"
local.resource # => ignored (unknown)

The count and for_each Meta-Arguments

TFLint supports the count and for_each meta-arguments.

resource "aws_instance" "foo" {
  count = 0

  instance_type = "invalid" # => ignored because ths resource is not created
}

resource "aws_instance" "foo" {
  count = 2

  instance_type = "t${count.index}.micro" # => "t0.micro" and "t1.micro"
}

Note that this behavior may differ depending on a rule. Rules like terraform_deprecated_syntax will check resources regardless of the meta-argument values.

If the meta-arguments are unknown, the resource/module is ignored:

variable "count" {}

resource "aws_instance" "foo" {
  count = var.count

  instance_type = "invalid" # => ignored
}

The path.* and terraform.workspace Values

TFLint supports filesystem and workspace info.

• path.module
• path.root
• path.cwd
• terraform.workspace.

Unsupported Named Values

The values below are state-dependent and cannot be determined statically, so TFLint resolves them to unknown values.

• <RESOURCE TYPE>.<NAME>
• module.<MODULE NAME>
• data.<DATA TYPE>.<NAME>
• self

Functions

Built-in Functions are fully supported. However, functions such as plantimestamp whose return value cannot be determined statically will return an unknown value.

Provider-defined functions always return unknown values, except for provider::terraform::* functions.

Dynamic Blocks

TFLint supports dynamic blocks.

resource "aws_instance" "dynamic" {
  dynamic "ebs_block_device" {
    for_each = toset([
      { size = 10 },
      { size = 20 }
    ])
    content {
      volume_size = ebs_block_device.value["size"] # => 10 and 20
    }
  }
}

Similar to support for meta-arguments, some rules may process a dynamic block as-is without expansion. If the for_each is unknown, the block will be empty.

Modules

TFLint doesn't automatically inspect the content of modules themselves. However, by default, it will analyze their content in order to raise any issues that arise from attributes in module calls.

resource "aws_instance" "static" {
  ebs_block_device {
    encrypted = false # => Must be encrypted
  }
}

module "aws_instance" {
  source = "./module/aws_instance"

  encrypted = false # => Must be encrypted
}

Remote modules can also be inspected. See Calling Modules for details.

Environment Variables

The following environment variables are supported:

• TF_VAR_name
• TF_DATA_DIR
• TF_WORKSPACE