allow configs without stacks (cloudtools#640)

* allow configs without stacks

This relaxes the current stack validation, replacing it instead with
action warning messages.

With this, configurations can be created with only hooks.

* update functional test

* Fix tests

* Fix output for warning when no stacks detected

* No longer throw error when configs missing stacks

stacker/actions/build.py

@@ -413,6 +413,8 @@ def run(self, concurrency=0, outline=False,
 
         """
         plan = self._generate_plan(tail=tail)
+        if not plan.keys():
+            logger.warn('WARNING: No stacks detected (error in config?)')
         if not outline and not dump:
             plan.outline(logging.DEBUG)
             logger.debug("Launching stacks: %s", ", ".join(plan.keys()))

stacker/actions/destroy.py

@@ -90,6 +90,8 @@ def pre_run(self, outline=False, *args, **kwargs):
 
     def run(self, force, concurrency=0, tail=False, *args, **kwargs):
         plan = self._generate_plan(tail=tail)
+        if not plan.keys():
+            logger.warn('WARNING: No stacks detected (error in config?)')
         if force:
             # need to generate a new plan to log since the outline sets the
             # steps to COMPLETE in order to log them

stacker/actions/diff.py

@@ -278,7 +278,10 @@ def _generate_plan(self):
     def run(self, concurrency=0, *args, **kwargs):
         plan = self._generate_plan()
         plan.outline(logging.DEBUG)
-        logger.info("Diffing stacks: %s", ", ".join(plan.keys()))
+        if plan.keys():
+            logger.info("Diffing stacks: %s", ", ".join(plan.keys()))
+        else:
+            logger.warn('WARNING: No stacks detected (error in config?)')
         walker = build_walker(concurrency)
         plan.execute(walker)
 

stacker/actions/info.py

@@ -18,6 +18,8 @@ class Action(BaseAction):
 
     def run(self, *args, **kwargs):
         logger.info('Outputs for stacks: %s', self.context.get_fqn())
+        if not self.context.get_stacks():
+            logger.warn('WARNING: No stacks detected (error in config?)')
         for stack in self.context.get_stacks():
             provider = self.build_provider(stack)
 

stacker/config/__init__.py

@@ -402,7 +402,7 @@ class Config(Model):
     lookups = DictType(StringType, serialize_when_none=False)
 
     stacks = ListType(
-        ModelType(Stack), default=[], validators=[not_empty_list])
+        ModelType(Stack), default=[])
 
     def _remove_excess_keys(self, data):
         excess_keys = set(data.keys())

stacker/tests/test_config.py

@@ -94,16 +94,6 @@ def test_config_validate_stack_class_and_template_paths(self):
             stack_errors['class_path'][0].__str__(),
             "template_path cannot be present when class_path is provided.")
 
-    def test_config_validate_no_stacks(self):
-        config = Config({"namespace": "prod"})
-        with self.assertRaises(exceptions.InvalidConfig) as ex:
-            config.validate()
-
-        error = ex.exception.errors['stacks'].errors[0]
-        self.assertEquals(
-            error.__str__(),
-            "Should have more than one element.")
-
     def test_config_validate_missing_name(self):
         config = Config({
             "namespace": "prod",

tests/test_suite/02_stacker_build_empty_config.bats

@@ -5,5 +5,5 @@ load ../test_helper
 @test "stacker build - empty config" {
   stacker build <(echo "")
   assert ! "$status" -eq 0
-  assert_has_line 'Should have more than one element'
+  assert_has_line 'stacker.exceptions.InvalidConfig:'
 }

tests/test_suite/03_stacker_build-config_with_no_stacks.bats

@@ -3,9 +3,11 @@
 load ../test_helper
 
 @test "stacker build - config with no stacks" {
+  needs_aws
+
   stacker build - <<EOF
 namespace: ${STACKER_NAMESPACE}
 EOF
-  assert ! "$status" -eq 0
-  assert_has_line 'Should have more than one element'
+  assert "$status" -eq 0
+  assert_has_line 'WARNING: No stacks detected (error in config?)'
 }