Validate AWS CloudFormation yaml/json templates against the AWS CloudFormation Resource Specification and additional checks. Includes checking valid values for resource properties and best practices.

This is an attempt to provide validation for AWS CloudFormation templates properties and their values. For values things can get pretty complicated (mappings, joins, splits, conditions, and nesting those functions inside each other) so it's a best effort to validate those values but the promise is to not fail if we can't understand or translate all the things that could be going on.

The Serverless Application Model (SAM) is supported by the linter. The template is transformed using AWS SAM before the linter processes the template.

To get information about the SAM Transformation, run the linter with --info

Python 2.7+ and 3.4+ are supported.

pip install cfn-lint. If pip is not available, run python setup.py clean --all then python setup.py install.

brew install cfn-lint

In cfn-python-lint source tree:

docker build --tag cfn-python-lint:latest .

In repository to be linted:

docker run --rm -v `pwd`:/data cfn-python-lint:latest /data/template.yaml

There are IDE plugins available to get direct linter feedback from you favorite editor:

• Atom
• Emacs
• NeoVim 0.2.0+/Vim 8
  • ALE
  • Coc
  • Syntastic
• Sublime
• Visual Studio Code
• IntelliJ IDEA

• cfn-lint template.yaml
• cfn-lint -t template.yaml

Multiple files can be linted by either specifying multiple specific files:

• cfn-lint template1.yaml template2.yaml
• cfn-lint -t template1.yaml template2.yaml

or by using wildcards (globbing):

Lint all yaml files in path:

• cfn-lint path/*.yaml

Lint all yaml files in path and all subdirectories (recursive):

• cfn-lint path/**/*.yaml

Note: Glob in Python 3.5 supports recursive searching **/*.yaml. If you are using an earlier version of Python you will have to handle this manually (folder1/*.yaml, folder2/*.yaml, etc).

cfn-lint will return a non zero exit if there are any issues with your template. The value is dependent on the sevirity of the issues found. For each level of discovered error cfn-lint will use bitwise OR to determine the final exit code. This will result in these possibilities.

• 0 is no issue was found
• 2 is an error
• 4 is a warning
• 6 is an error and a warning
• 8 is an informational
• 10 is an error and informational
• 12 is an warning and informational
• 14 is an error and a warning and an informational

The template to be linted can also be passed using standard input:

• cat path/template.yaml | cfn-lint -

• cfn-lint -r us-east-1 ap-south-1 -- template.yaml
• cfn-lint -r us-east-1 ap-south-1 -t template.yaml

From a command prompt run cfn-lint <path to template> to run standard linting of the template.

It will look for a configuration file in the following locations (by order of preference):

• .cfnlintrc, .cfnlintrc.yaml or .cfnlintrc.yml in the current working directory
• ~/.cfnlintrc for the home directory

In that file you can specify settings from the parameter section below.

Example:

templates:
  - test/fixtures/templates/good/**/*.yaml
ignore_templates:
  - codebuild.yaml
include_checks:
  - I

Optional parameters:

To maintain backwards compatibility info rules are not included by default. To include these rules you will need to include -c I or --include-checks I

Inside the root level Metadata key you can configure cfn-lint using the supported parameters.

Metadata:
  cfn-lint:
    config:
      regions:
        - us-east-1
        - us-east-2
      ignore_checks:
        - E2530

Inside a resources Metadata key you can configure cfn-lint to ignore checks. This will filter out failures for the resource in which the Metadata belongs. Keep in mind that AWS::Serverless resources may lose metadata during the Serverless transform

Resources:
  myInstance:
    Type: AWS::EC2::Instance
    Metadata:
      cfn-lint:
        config:
          ignore_checks:
            - E3030
    Properties:
      InstanceType: nt.x4superlarge
      ImageId: ami-abc1234

cfn-lint applies configurations from several sources. The rules at lower levels are overridden by those at higher levels.

1. cfnlintrc configurations
2. Template Metadata configurations
3. CLI parameters

Certain rules support configuration properties. You can configure these rules by using configure_rules parameter.

From the command line the format is RuleId:key=value, for example: E3012:strict=false. From the cfnlintrc or Metadata section the format is

Metadata:
  cfn-lint:
    config:
      configure_rules:
        RuleId:
          key: value

The configurable rules have a non-empty Config entry in the table here.

There are getting started guides available in the documentation section to help with integrating cfn-lint or creating rules.

This linter checks the AWS CloudFormation template by processing a collection of Rules, where every rule handles a specific function check or validation of the template.

This collection of rules can be extended with custom rules using the --append-rules argument.

More information describing how rules are set up and an overview of all the Rules that are applied by this linter are documented here.

The linter follows the AWS CloudFormation Resource Specifications by default. However, for your use case specific requirements might exist. For example, within your organisation it might be mandatory to use Tagging.

The linter provides the possibility to implement these customized specifications using the --override-spec argument.

More information about how this feature works is documented here

If you'd like cfn-lint to be run automatically when making changes to files in your Git repository, you can install pre-commit and add the following text to your repositories' .pre-commit-config.yaml:

repos:
- repo: https://github.com/aws-cloudformation/cfn-python-lint
  rev: v0.47.2  # The version of cfn-lint to use
  hooks:
    - id: cfn-python-lint
      files: path/to/cfn/dir/.*\.(json|yml|yaml)$

• If you exclude the files: line above, every json/yml/yaml file will be checked.
• You can see available cfn-lint versions on the releases page.