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Lightweight, extensible schema and data validation tool for Cloudformation Templates.

Project description

Cloudformation-Validator

Features

cloudformation_validator provides type checking and other base functionality out of the box and is designed to be non-blocking and easily extensible, allowing for custom validation. It has no dependencies and is thoroughly tested under Python 2.7, Python 3.3, Python 3.4, Python 3.5, Python 3.6.

Funding

cloudformation_validator is a open source, collaboratively funded project. If you run a business and are using cloudformation_validator in a revenue-generating product, it would make business sense to sponsor its development: it ensures the project that your product relies on stays healthy and actively maintained. Individual users are also welcome to make a recurring pledge or a one time donation if cfn-validator has helped you in your work or personal projects.

Every single sign-up makes a significant impact towards making cloudformation_validator possible.

Want Custom Rules and Support For Your Application

Submit an issue on my github page if you would like additional custom rules and I will try and get them added as soon as possible.

I you would like other functionality, just submit an issue and I will see what I can do to get it added.

Installation

cloudformation-validator is on PyPI so all you need is:

$ pip install cfn-validator

Demonstration

Cloudformation Validator tutorial

Just run:

$ pip install virtualenv
$ which python
$ virtualenv ~/virtualenvs/my_project -p /home/example_username/opt/python-3.6.2/bin/python3
$ git clone https://github.com/rubelw/cloudformation-validator.git
$ cd cloudformation-validator
$ pip install -r requirements-dev.txt
$ python setup.py install --force
$ python setup.py test}

Or you can use tox to run the tests under all supported Python versions. Make sure the required python versions are installed and run:

$ pip install virtualenv
$ which python
$ virtualenv ~/virtualenvs/my_project -p /home/example_username/opt/python-3.6.2/bin/python3
$ git clone https://github.com/rubelw/cloudformation-validator.git
$ cd cloudformation-validator
$ pip install -r requirements-dev.txt
$ python setup.py install --force
$ pip install tox  # first time only
$ tox}

Listing Rules

$ cfn-validator dump_rules
##################################
########## WARNINGS ##############
##################################
{'id': 'F4', 'type': 'VIOLATION::WARNING', 'message': 'IAM policy should not allow * action'}
{'id': 'W1', 'type': 'VIOLATION::WARNING', 'message': 'Specifying credentials in the template itself is probably not the safest thing'}
...

Example

Getting help

$ cfn-validator validate --help
Usage: cfn-validator validate [OPTIONS]

  primary function for validating a template :param template_path: :param
  template_file: :param debug: :param rules_directory: :param profile_path:
  :param allow_suppression: :param print_suppression: :param
  parameter_values_path: :param isolate_custom_rule_exceptions: :param
  version: :return:

Options:
  -s, --suppress-errors           Whether to suppress misc errors to get hash only
  -t, --template-path TEXT        base directory to search for templates
  -f, --template-file TEXT        single_template_file
  --debug                         Turn on debugging
  -r, --rules-directory TEXT      Extra rule directory
  -o, --profile-path TEXT         Path to a profile file
  --allow-suppression / --no-allow-suppression
                                  Allow using Metadata to suppress violations
  -p, --print-suppression         Emit suppressions to stderr
  -m, --parameter-values-path TEXT
                                  Path to a JSON file to pull Parameter values
                                  from
  -i, --isolate-custom-rule-exceptions
                                  Isolate custom rule exceptions - just emit
                                  the exception without stack trace and keep
                                  chugging
  -v, --version                   Print version and exit
  --help                          Show this message and exit.

Validate a file

$cfn-validator validate -f cloudfront_distribution_without_logging.json

Evaluating: cloudfront_distribution_without_logging.json
[
    {
        'failure_count': '0',
        'filename': 'cloudfront_distribution_without_logging.json',
        'file_results': [
            {
                'id': 'W10',
                'type': 'VIOLATION::WARNING',
                'message': 'CloudFront Distribution should enable access logging',
                'logical_resource_ids': [
                    'rDistribution2'
                ]
            }
        ]
    }
]

Validate all files in a path

$cfn-validator validate -f /projects
...

Programmatically call cfn-validator to analyze a file

from cloudformation_validator.ValidateUtility import ValidateUtility

config_dict = {}
config_dict['template_file'] = '/tmp/template.json'
validator = ValidateUtility(config_dict)
real_result =  validator.validate()
print(real_result)

[
    {
        'failure_count': '0',
        'filename': '/tmp/template.json',
        'file_results': [
            {
                'id': 'W1',
                'type': 'VIOLATION::WARNING',
                'message': 'Specifying credentials in the template itself is probably not the safest thing',
                'logical_resource_ids': [
                    'EC2I4LBA1'
                ]
            }
        ]
    }
]

I you get some errors and warnings in your out put, you can pass-in the flag to suppress all errors

from cloudformation_validator.ValidateUtility import ValidateUtility

config_dict = {}
config_dict['suppress_errors'] = True
config_dict['template_file'] = '/tmp/template.json'
validator = ValidateUtility(config_dict)
real_result =  validator.validate()
print(real_result)

[
    {
        'failure_count': '0',
        'filename': '/tmp/template.json',
        'file_results': [
            {
                'id': 'W1',
                'type': 'VIOLATION::WARNING',
                'message': 'Specifying credentials in the template itself is probably not the safest thing',
                'logical_resource_ids': [
                    'EC2I4LBA1'
                ]
            }
        ]
    }
]

Writing your own rules

  • Utilize the format for existing rules in the /cloudformation_validator/custom_rules directory
  • Places the files in a new directory
  • The __init__, rule_text, rule_type and rule_id methods should be amount the same, just change of the rule, the text for a failure, and the type to either 'VIOLATION::FAILING_VIOLATION' or VIOLATION::WARNNING'
  • Set the id to 'W' for warnings, and 'F' for failure. Pick a number not utilized elsewhere...
  • NOTE: Currently working on functionality for controlling and listing rules
  • For the audit_impl function - portion with will test the resource objects, you will need to review the object model for the resource to see what objects are available, and then review the parser for the resource. Also, look at other similar rules for the resource, and model after them. The basic concept of the function is to identify resources which apply, iterate over the selected resources, and identify specific aspects to evaluate in the rule
  • pass in the --rules-directory /directory in the command line, and the extra rules directory will get added to the existing rules
def audit_impl(self):

  violating_rules = []

  # This defines which type of resource we are going to test
  resources = self.cfn_model.resources_by_type('AWS::SQS::QueuePolicy')

  if len(resources)>0:
    for resource in resources:
        if hasattr(resource, 'policy_document'):
          if resource.policy_document:
            if resource.policy_document.wildcard_allowed_actions():
              violating_rules.append(resource.logical_resource_id)

  return violating_rules

Example of writing a rule which requires custom tags for EC2 instances

  • Create a directory to store your custom rule
  • Create the custom rule
mkdir ~/custom_validator_rules
from __future__ import absolute_import, division, print_function
import inspect
import sys
from builtins import (str)
from cloudformation_validator.custom_rules.BaseRule import BaseRule
from collections import Iterable
from six import StringIO, string_types
from builtins import (str)

class Ec2CustomTagsRule(BaseRule):

  def __init__(self, cfn_model=None, debug=None):
    '''
    Initialize Ec2HasTagsRule
    :param cfn_model:
    '''
    BaseRule.__init__(self, cfn_model, debug=debug)

  def rule_text(self):
    '''
    Returns rule text
    :return:
    '''
    if self.debug:
      print('rule_text')
    return 'EC2 instance does not have the required tags'

  def rule_type(self):
    '''
    Returns rule type
    :return:
    '''
    self.type= 'VIOLATION::FAILING_VIOLATION'
    return 'VIOLATION::FAILING_VIOLATION'

  def rule_id(self):
    '''
    Returns rule id
    :return:
    '''
    if self.debug:
      print('rule_id')
    self.id ='F86'
    return 'F86'

  def tags_to_dict(self, aws_tags):
        """ Convert a list of AWS tags into a python dict """
        return {str(tag['Key']): str(tag['Value']) for tag in self.ensure_list(aws_tags)}

  def ensure_list(self, value):
        """
        Coerces a variable into a list; strings will be converted to a singleton list,
        and `None` or an empty string will be converted to an empty list.
        Args:
            value: a list, or string to be converted into a list.

        Returns:
            :py:class:`list`
        """
        ret_value = value
        if not value:
            ret_value = []
        elif not isinstance(value, Iterable) or isinstance(value, string_types):
            ret_value = [value]
        return ret_value


  def audit_impl(self):
    '''
    Audit
    :return: violations
    '''
    if self.debug:
      print('Ec2HasTagsRule - audit_impl')

    violating_volumes = []

    resources = self.cfn_model.resources_by_type('AWS::EC2::Instance')

    if len(resources) > 0:

      for resource in resources:
        if self.debug:
          print('resource: ' + str(resource))
          print('vars: '+str(vars(resource)))

        if hasattr(resource, 'tags'):
          tags_dict = self.tags_to_dict(resource.cfn_model['Properties']['Tags'])
          required_tags = ('Name', 'ResourceOwner','DeployedBy','Project')
          if not set(required_tags).issubset(tags_dict):
            violating_volumes.append(str(resource.logical_resource_id))
        else:
          if self.debug:
            print('does not tags property')
          violating_volumes.append(str(resource.logical_resource_id))

    else:
      if self.debug:
        print('no violating_volumes')

    return violating_volumes
  • Test the rule by creating a cloudformation template without the necessary tags and testing
{
  "Parameters": {
    "subnetId": {
      "Type": "String",
      "Default": "subnet-4fd01116"
    }
  },

  "Resources": {
    "EC2I4LBA1": {
      "Type": "AWS::EC2::Instance",
      "Properties": {
        "ImageId": "ami-6df1e514",
        "InstanceType": "t2.micro",
        "SubnetId": {
          "Ref": "subnetId"
        }
      },
      "Metadata": {
        "AWS::CloudFormation::Authentication": {
          "testBasic" : {
            "type" : "basic",
            "username" : "biff",
            "password" : "badpassword",
            "uris" : [ "http://www.example.com/test" ]
          }
        }
      }
    }
  }
}
  • Run the test
cfn-validator validate --template-file=/tmp/template.json --rules-directory=/home/user/custom_validator_rules}
  • You should receive the following violations
{
    'failure_count': '1',
    'filename': '/tmp/template.json',
    'file_results': [
        {
            'id': 'F86',
            'type': 'VIOLATION::FAILING_VIOLATION',
            'message': 'EC2 instance does not have the required tags',
            'logical_resource_ids': [
                'EC2I4LBA1'
            ]
        },
        {
            'id': 'W1',
            'type': 'VIOLATION::WARNING',
            'message': 'Specifying credentials in the template itself is probably not the safest thing',
            'logical_resource_ids': [
                'EC2I4LBA1'
            ]
        }
    ]
}
  • No add tags property to the cloudformation template and run again
{
"Parameters": {
"subnetId": {
"Type": "String",
"Default": "subnet-4fd01116"
}
},}
"Resources": {
  "EC2I4LBA1": {
    "Type": "AWS::EC2::Instance",
    "Properties": {
      "ImageId": "ami-6df1e514",
      "InstanceType": "t2.micro",
      "SubnetId": {
        "Ref": "subnetId"
      },
      "Tags" : [
        {"Key" : "Name", "Value":"value"},
        {"Key":"ResourceOwner","Value":"resourceowner"},
        {"Key":"DeployedBy","Value":"deployedby"},
        {"Key":"Project","Value":"project"}
      ]
    },
    "Metadata": {
      "AWS::CloudFormation::Authentication": {
        "testBasic" : {
          "type" : "basic",
          "username" : "biff",
          "password" : "badpassword",
          "uris" : [ "http://www.example.com/test" ]
        }
      }
    }
  }
}

}

  • You should receive the following violations
{
'failure_count': '0',
'filename': '/tmp/template.json',
'file_results': [
{
'id': 'W1',
'type': 'VIOLATION::WARNING',
'message': 'Specifying credentials in the template itself is probably not the safest thing',
'logical_resource_ids': [
'EC2I4LBA1'
]
}
]
}}

Unit Testing

Run unit tests

(python3) => pytest
================================================ test session starts =================================================
collected 22 items

test/test_cloudfront_distribution.py .                                                                         [  4%]
test/test_ec2_instance.py .                                                                                    [  9%]
test/test_ec2_volume.py ..                                                                                     [ 18%]
test/test_elasticloadbalancing_loadbalancer.py .                                                               [ 22%]
test/test_iam_user.py .                                                                                        [ 27%]
test/test_lambda_permission.py .                                                                               [ 31%]
test/test_rds_instance.py ...                                                                                  [ 45%]
test/test_s3_bucket.py .                                                                                       [ 50%]
test/test_s3_bucket_policy.py .                                                                                [ 54%]
test/test_security_group.py ........                                                                           [ 90%]
test/test_sns_policy.py .                                                                                      [ 95%]
test/test_sqs_policy.py .                                                                                      [100%]

Source

I am just getting started on this, so any suggestions would be welcome. <https://github.com/rubelw/cloudformation-validator>

Copyright

cloudformation_validator is an open source project by Will Rubel <https://www.linkedin.com/in/will-rubel-03205b2a/>, that was ported from a ruby project by Stelligent. See the original LICENSE information <https://github.com/stelligent/cfn_nag/blob/master/LICENSE.md>.

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