Merge pull request #20 from remind101/use_existing_params

Use existing params

stacker/blueprints/base.py

@@ -31,15 +31,16 @@ def __init__(self, name, context, mappings=None):
 
     @property
     def parameters(self):
-        params = []
-        for param in self.template.parameters:
-            try:
-                params.append((param, self.context.parameters[param]))
-            except KeyError:
-                logger.debug("Parameter '%s' not found in context, skipping.",
-                             param)
-                continue
-        return params
+        return self.template.parameters
+
+    @property
+    def required_parameters(self):
+        """ Returns all parameters that do not have a default value. """
+        required = []
+        for k, v in self.parameters.items():
+            if not hasattr(v, 'Default'):
+                required.append((k, v))
+        return required
 
     def setup_parameters(self):
         t = self.template

stacker/builder.py

@@ -13,6 +13,17 @@
                    COMPLETE_STATUSES)
 
 
+class MissingParameterException(Exception):
+    def __init__(self, blueprint, parameters):
+        self.blueprint = blueprint
+        self.parameter = parameters
+        self.message = "Blueprint %s missing required parameters: %s" % (
+            blueprint, ', '.join(parameters))
+
+    def __str__(self):
+        return self.message
+
+
 class Builder(object):
     """ Responsible for building & coordinating CloudFormation stacks.
 
@@ -144,17 +155,18 @@ def build_blueprint(self, stack_context):
         self.plan[stack_name].blueprint = blueprint
         return blueprint
 
-    def resolve_parameters(self, parameters, blueprint):
+    def resolve_parameters(self, parameters, blueprint, existing_stack=None):
         """ Resolves parameters for a given blueprint.
 
         Given a list of parameters, first discard any parameters that the
         blueprint does not use. Then, if a remaining parameter is in the format
         <stack_name>::<output_name>, pull that output from the foreign
         stack.
         """
-        params = []
+        params = {}
+        blueprint_params = blueprint.parameters
         for k, v in parameters.items():
-            if k not in blueprint.template.parameters:
+            if k not in blueprint_params:
                 logger.debug("Template %s does not use parameter %s.",
                              blueprint.name, k)
                 continue
@@ -164,8 +176,23 @@ def resolve_parameters(self, parameters, blueprint):
                 stack_name, output = value.split('::')
                 self.get_outputs(stack_name)
                 value = self.outputs[stack_name][output]
-            params.append((k, value))
-        return params
+            params[k] = value
+        # Deal w/ missing parameters
+        required_params = [k for k, v in blueprint.required_parameters]
+        missing_params = list(set(required_params) - set(params.keys()))
+        if existing_stack:
+            stack_params = {p.key: p.value for p in existing_stack.parameters}
+            for p in missing_params:
+                if p in stack_params:
+                    value = stack_params[p]
+                    logger.debug("Using parameter %s from existing stack: %s",
+                                 p, value)
+                    params[p] = value
+        final_missing = list(set(required_params) - set(params.keys()))
+        if final_missing:
+            raise MissingParameterException(blueprint.name, final_missing)
+
+        return params.items()
 
     def get_stack(self, stack_full_name):
         """ Give a stacks full name, query for the boto Stack object.
@@ -232,7 +259,7 @@ def launch_stack(self, stack_name, blueprint):
         template_url = self.s3_stack_push(blueprint)
         tags = self.build_stack_tags(stack_context, template_url)
         parameters = self.resolve_parameters(stack_context.parameters,
-                                             blueprint)
+                                             blueprint, stack)
         submitted = False
         if not stack:
             submitted = self.create_stack(full_name, template_url, parameters,
@@ -249,9 +276,9 @@ def get_outputs(self, stack_name, force=False):
 
         Updates the local output cache with the values it finds.
         """
-        logger.debug("Getting outputs from stack %s.", stack_name)
         if stack_name in self.outputs and not force:
             return
+        logger.debug("Getting outputs from stack %s.", stack_name)
 
         full_name = self.get_stack_full_name(stack_name)
         stack = self.conn.cloudformation.describe_stacks(full_name)[0]