allow raw cfn templates to be loaded from remote package_sources (#638)

* allow raw cfn templates to be loaded from remote package_sources

Fixes #628

* add test for new get_template_path function

docs/config.rst

@@ -340,7 +340,11 @@ A stack has the following keys:
   ``template_path`` for the stack.
 **template_path:**
   Path to raw CloudFormation template (JSON or YAML). Specify this or
-  ``class_path`` for the stack.
+  ``class_path`` for the stack. Path can be specified relative to the current
+  working directory (e.g. templates stored alongside the Config), or relative
+  to a directory in the python ``sys.path`` (i.e. for loading templates
+  retrieved via ``packages_sources``).
+
 **description:**
   A short description to apply to the stack. This overwrites any description
   provided in the Blueprint. See: http://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/template-description-structure.html

stacker/blueprints/raw.py

@@ -5,12 +5,36 @@
 
 import hashlib
 import json
+import os
+import sys
 
 from ..util import parse_cloudformation_template
-from ..exceptions import UnresolvedVariable
+from ..exceptions import InvalidConfig, UnresolvedVariable
 from .base import Blueprint
 
 
+def get_template_path(filename):
+    """Find raw template in working directory or in sys.path.
+
+    template_path from config may refer to templates colocated with the Stacker
+    config, or files in remote package_sources. Here, we emulate python module
+    loading to find the path to the template.
+
+    Args:
+        filename (str): Template filename.
+
+    Returns:
+        Optional[str]: Path to file, or None if no file found
+
+    """
+    if os.path.isfile(filename):
+        return filename
+    for i in sys.path:
+        if os.path.isfile(os.path.join(i, filename)):
+            return os.path.join(i, filename)
+    return None
+
+
 def get_template_params(template):
     """Parse a CFN template for defined parameters.
 
@@ -159,8 +183,15 @@ def requires_change_set(self):
     def rendered(self):
         """Return (generating first if needed) rendered template."""
         if not self._rendered:
-            with open(self.raw_template_path, 'r') as template:
-                self._rendered = template.read()
+            template_path = get_template_path(self.raw_template_path)
+            if template_path:
+                with open(template_path, 'r') as template:
+                    self._rendered = template.read()
+            else:
+                raise InvalidConfig(
+                    'Could not find template %s' % self.raw_template_path
+                )
+
         return self._rendered
 
     @property

stacker/tests/blueprints/test_raw.py

@@ -3,11 +3,15 @@
 from __future__ import division
 from __future__ import absolute_import
 import json
+import os
+import sys
 import unittest
 
 from mock import MagicMock
 
-from stacker.blueprints.raw import get_template_params, RawTemplateBlueprint
+from stacker.blueprints.raw import (
+    get_template_params, get_template_path, RawTemplateBlueprint
+)
 from ..factories import mock_context
 
 RAW_JSON_TEMPLATE_PATH = 'stacker/tests/fixtures/cfn_template.json'
@@ -17,6 +21,32 @@
 class TestRawBluePrintHelpers(unittest.TestCase):
     """Test class for functions in module."""
 
+    def test_get_template_path_local_file(self):  # noqa pylint: disable=invalid-name
+        """Verify get_template_path finding a file relative to CWD."""
+        self.assertEqual(get_template_path(RAW_YAML_TEMPLATE_PATH),
+                         RAW_YAML_TEMPLATE_PATH)
+
+    def test_get_template_path_invalid_file(self):  # noqa pylint: disable=invalid-name
+        """Verify get_template_path with an invalid filename."""
+        self.assertEqual(get_template_path('afilenamethatdoesnotexist.txt'),
+                         None)
+
+    def test_get_template_path_file_in_syspath(self):  # noqa pylint: disable=invalid-name
+        """Verify get_template_path with a file in sys.path.
+
+        This ensures templates are able to be retreived from remote packages.
+
+        """
+        stacker_tests_dir = os.path.dirname(os.path.dirname(os.path.realpath(__file__)))  # noqa
+        old_sys_path = list(sys.path)
+        sys.path.append(stacker_tests_dir)
+        try:
+            self.assertEqual(get_template_path('fixtures/cfn_template.yaml'),
+                             os.path.join(stacker_tests_dir,
+                                          'fixtures/cfn_template.yaml'))
+        finally:
+            sys.path = old_sys_path
+
     def test_get_template_params(self):
         """Verify get_template_params function operation."""
         template_dict = {