CloudFormation YAML Assembler

c12n-assemble.py

#!/usr/bin/env python2.7
# -*- coding: utf-8 -*-

import argparse
import glob
import json
import os
import sys
import yaml

def __main__():
    parser = argparse.ArgumentParser(
        description="Creates a CloudFormation JSON config from a series of YAML files."
    )

    # optional args
    parser.add_argument('-o', '--output', type=argparse.FileType('wb'), default=sys.stdout,
        help="The output file to write. Defaults to standard output.")

    # required args
    parser.add_argument('base_file', type=argparse.FileType('rb'),
        help="The base YAML file for the CloudFormation template.")

    args = parser.parse_args()

    assembler = CloudFormationAssembler(base_file=args.base_file, output_file=args.output)
    assembler.assemble()

class CloudFormationAssembler(object):

    def __init__(self, base_file, output_file):
        self.__result = None
        self.__base_file = base_file
        self.__base_dir = os.path.dirname(base_file.name)
        self.__output_file = output_file

    def assemble(self):
        # load the base file
        self.__result = yaml.safe_load(self.__base_file)

        # load all mappings
        self.assemble_chunks('mappings', 'Mappings', self.__result)
        self.assemble_chunks('parameters', 'Parameters', self.__result)
        self.assemble_chunks('resources', 'Resources', self.__result)

        # write to output as pretty JSON
        json.dump(self.__result, self.__output_file, sort_keys=True, indent=4, separators=(',', ': '))

    def assemble_chunks(self, path, dest_key, target):
        if os.path.isdir(os.path.join(self.__base_dir, path)):
            for chunk in glob.glob(os.path.join(self.__base_dir, path, '*.yml')):
                # if the destination key doesn't exist in target, initialize as array
                if not dest_key in target.keys() or type(target.get(dest_key)) != dict:
                    target[dest_key] = {}

                with open(chunk, 'rb') as f:
                    target[dest_key].update(yaml.safe_load(f))

if __name__ == "__main__":
    __main__()

example-layout

.
├── mappings
│   └── mappings.yml
├── parameters
│   └── instance_types.yml
├── resources
│   ├── ec2_instances.yml
│   └── ecs_services.yml
├── c12n-assemble
├── input.yml
└── README.md