kadrach / tflint

A Pluggable Terraform Linter

TFLint

A Pluggable Terraform Linter

Features

TFLint is a framework and each feature is provided by plugins, the key features are as follows:

• Find possible errors (like illegal instance types) for Major Cloud providers (AWS/Azure/GCP).
• Warn about deprecated syntax, unused declarations.
• Enforce best practices, naming conventions.

Installation

Bash script (Linux):

curl -s https://raw.githubusercontent.com/terraform-linters/tflint/master/install_linux.sh | bash

Homebrew (macOS):

brew install tflint

Chocolatey (Windows):

choco install tflint

Docker

Instead of installing directly, you can use the Docker images:

Name	Description
ghcr.io/terraform-linters/tflint	Basic image
ghcr.io/terraform-linters/tflint-bundle	A Docker image with TFLint and ruleset plugins

Example:

docker run --rm -v $(pwd):/data -t ghcr.io/terraform-linters/tflint

GitHub Actions

If you want to run on GitHub Actions, setup-tflint action is available.

Getting Started

If you are using an AWS/Azure/GCP provider, it is a good idea to install the plugin and try it according to each usage:

• Amazon Web Services
• Microsoft Azure
• Google Cloud Platform

Rules for the Terraform Language is built into the TFLint binary, so you don't need to install any plugins. Please see Rules for a list of available rules.

If you want to extend TFLint with other plugins, you can declare the plugins in the config file and easily install them with tflint --init.

plugin "foo" {
  enabled = true
  version = "0.1.0"
  source  = "github.com/org/tflint-ruleset-foo"

  signing_key = <<-KEY
  -----BEGIN PGP PUBLIC KEY BLOCK-----

  mQINBFzpPOMBEADOat4P4z0jvXaYdhfy+UcGivb2XYgGSPQycTgeW1YuGLYdfrwz
  9okJj9pMMWgt/HpW8WrJOLv7fGecFT3eIVGDOzyT8j2GIRJdXjv8ZbZIn1Q+1V72
  AkqlyThflWOZf8GFrOw+UAR1OASzR00EDxC9BqWtW5YZYfwFUQnmhxU+9Cd92e6i
  ...
  KEY
}

See also Configuring Plugins.

Usage

TFLint inspects files under the current directory by default. You can change the behavior with the following options/arguments:

$ tflint --help
Usage:
  tflint [OPTIONS] [FILE or DIR...]

Application Options:
  -v, --version                                           Print TFLint version
      --init                                              Install plugins
      --langserver                                        Start language server
  -f, --format=[default|json|checkstyle|junit|compact]    Output format (default: default)
  -c, --config=FILE                                       Config file name (default: .tflint.hcl)
      --ignore-module=SOURCE                              Ignore module sources
      --enable-rule=RULE_NAME                             Enable rules from the command line
      --disable-rule=RULE_NAME                            Disable rules from the command line
      --only=RULE_NAME                                    Enable only this rule, disabling all other defaults. Can be specified multiple times
      --enable-plugin=PLUGIN_NAME                         Enable plugins from the command line
      --var-file=FILE                                     Terraform variable file name
      --var='foo=bar'                                     Set a Terraform variable
      --module                                            Inspect modules
      --force                                             Return zero exit status even if issues found
      --no-color                                          Disable colorized output
      --loglevel=[trace|debug|info|warn|error]            Change the loglevel

Help Options:
  -h, --help                                              Show this help message

See User Guide for details.

FAQ

Does TFLint check modules recursively?

No. TFLint always checks only the current root module (no recursive check). However, you can check calling child modules based on module arguments by enabling Module Inspection. This allows you to check that you are not passing illegal values to the module.

Note that if you want to recursively inspect local modules, you need to run them in each directory. This is a limitation that occurs because Terraform always works for one directory. TFLint tries to emulate Terraform's semantics, so cannot perform recursive inspection.

Do I need to install Terraform for TFLint to work?

No. TFLint works as a single binary because Terraform is embedded as a library. Note that this means that the version of Terraform used is determined for each TFLint version. See also Compatibility with Terraform.

TFLint reports a loading error in my code, but this is valid in Terraform. Why?

First, check the version of Terraform and TFLint you are using. TFLint loads files differently than the installed Terraform, so an error can occur if the version of Terraform supported by TFLint is different from the installed Terraform.

Debugging

If you don't get the expected behavior, you can see the detailed logs when running with TFLINT_LOG environment variable.

$ TFLINT_LOG=debug tflint

Developing

See Developer Guide.

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