Packer build wrapper for generating JSON from a more flexible YAML config syntax

build.py

#!/usr/bin/python
#
# "packer build" wrapper that sets up a consistent build environment for image building.
#
# - Use common .packer_cache directory in this root directory
# - Generate JSON templates from YAML (if exists) to allow comments and includes

import sys
import os
import subprocess
import yaml
import json
import tempfile
import code


class IncludeLoader(yaml.Loader):

    def __init__(self, stream):
        self._root = os.path.split(stream.name)[0]
        super(IncludeLoader, self).__init__(stream)

    def include(self, node):
        filename = os.path.join(self._root, self.construct_scalar(node))
        with open(filename, 'r') as f:
            return yaml.load(f, IncludeLoader)

IncludeLoader.add_constructor('!include', IncludeLoader.include) 

def build_image(path):
	
	if path and path[-1:] == '/':
		path = path[:-1]

	if not os.path.exists(path):
		print "[ERROR] Unable to build image %s: no templates found" % path
		sys.exit(1)

	name = os.path.basename(path)
	yaml_template = "%s/%s.yaml" % (path, name)
	json_template = "%s/%s.json" % (path, name)
	remove_json = False

	if os.path.exists(yaml_template):

		if os.path.exists(json_template):
			print "[WARNING] %s: Found both JSON and YAML templates, using YAML" % path

		with open(yaml_template, 'r') as infile:
			template = yaml.load(infile, IncludeLoader)

			# Flatten provisioners so we can include multiple steps in each include
			if 'provisioners' in template:
				prov = template['provisioners']
				flat = []
				for p in prov:
					if isinstance(p, list):
						flat.extend(p)
					else:
						flat.append(p)
				template['provisioners'] = flat

			(outfile, json_template) = tempfile.mkstemp('.json', 'packer')
			remove_json = True
			with open(json_template, 'w') as outfile:
				json.dump(template, outfile)

	if os.path.exists(json_template):

		cwd = os.getcwd()
		packer_env = os.environ.copy()
		packer_env['PACKER_CACHE_DIR'] = '%s/.packer_cache' % cwd
		p = subprocess.Popen(['packer', 'build', '-force', json_template], env=packer_env)

		try:
			p.wait()
		except KeyboardInterrupt:
			p.wait()
		finally:
			if remove_json:
				os.unlink(json_template)
	
	else:
		print "[ERROR] Unable to build image %s: no templates found" % path
		sys.exit(1)

if __name__ == "__main__":
	for path in sys.argv[1:]:
		build_image(path)