From 70a7a7e0a0bcb6bcfde3a1d2394caa28a37b92a8 Mon Sep 17 00:00:00 2001
From: Sahil Shah <53784576+sahilshah6196@users.noreply.github.com>
Date: Tue, 29 Jun 2021 13:28:52 -0400
Subject: [PATCH] SSM parameters in cloudformation (AWS::SSM::Parameter::) are
 not recognized and resolved for default values (#4042)

* Add ssm parsing support for cloudformation stacks
---
 moto/cloudformation/parsing.py                | 34 +++++++++----------
 .../test_cloudformation/test_stack_parsing.py | 20 ++++++++++-
 2 files changed, 36 insertions(+), 18 deletions(-)

diff --git a/moto/cloudformation/parsing.py b/moto/cloudformation/parsing.py
index 0b5f13aae..77175fd3e 100644
--- a/moto/cloudformation/parsing.py
+++ b/moto/cloudformation/parsing.py
@@ -504,11 +504,26 @@ class ResourceMap(collections_abc.Mapping):
                     key = s3_backend.get_object(bucket_name, name)
                     self._parsed_resources.update(json.loads(key.value))
 
+    def parse_ssm_parameter(self, value, value_type):
+
+        # The Value in SSM parameters is the SSM parameter path
+        # we need to use ssm_backend to retreive the
+        # actual value from parameter store
+        parameter = ssm_backends[self._region_name].get_parameter(value, False)
+        actual_value = parameter.value
+        if value_type.find("List") > 0:
+            return actual_value.split(",")
+        return actual_value
+
     def load_parameters(self):
         parameter_slots = self._template.get("Parameters", {})
         for parameter_name, parameter in parameter_slots.items():
             # Set the default values.
-            self.resolved_parameters[parameter_name] = parameter.get("Default")
+            value = parameter.get("Default")
+            value_type = parameter.get("Type")
+            if value_type.startswith("AWS::SSM::Parameter::") and value:
+                value = self.parse_ssm_parameter(value, value_type)
+            self.resolved_parameters[parameter_name] = value
 
         # Set any input parameters that were passed
         self.no_echo_parameter_keys = []
@@ -517,23 +532,8 @@ class ResourceMap(collections_abc.Mapping):
                 parameter_slot = parameter_slots[key]
 
                 value_type = parameter_slot.get("Type", "String")
-
-                def _parse_ssm_parameter(value, value_type):
-                    # The Value in SSM parameters is the SSM parameter path
-                    # we need to use ssm_backend to retreive the
-                    # actual value from parameter store
-                    parameter = ssm_backends[self._region_name].get_parameter(
-                        value, False
-                    )
-                    actual_value = parameter.value
-
-                    if value_type.find("List") > 0:
-                        return actual_value.split(",")
-
-                    return actual_value
-
                 if value_type.startswith("AWS::SSM::Parameter::"):
-                    value = _parse_ssm_parameter(value, value_type)
+                    value = self.parse_ssm_parameter(value, value_type)
                 if value_type == "CommaDelimitedList" or value_type.startswith("List"):
                     value = value.split(",")
 
diff --git a/tests/test_cloudformation/test_stack_parsing.py b/tests/test_cloudformation/test_stack_parsing.py
index e1b1dc812..843b1b22c 100644
--- a/tests/test_cloudformation/test_stack_parsing.py
+++ b/tests/test_cloudformation/test_stack_parsing.py
@@ -78,7 +78,10 @@ parameters = {
 ssm_parameter = {
     "Parameters": {
         "SingleParamCfn": {"Type": "AWS::SSM::Parameter::Value<String>"},
-        "ListParamCfn": {"Type": "AWS::SSM::Parameter::Value<List<String>>"},
+        "ListParamCfn": {
+            "Type": "AWS::SSM::Parameter::Value<List<String>>",
+            "Default": "/path/to/list/param",
+        },
     }
 }
 
@@ -537,3 +540,18 @@ def test_ssm_parameter_parsing():
         stack.resource_map.resolved_parameters["ListParamCfn"].should.equal(
             ["comma", "separated", "string"]
         )
+
+    # Not passing in a value for ListParamCfn to test Default value
+    if not settings.TEST_SERVER_MODE:
+        stack = FakeStack(
+            stack_id="test_id",
+            name="test_stack",
+            template=ssm_parameter_template_json,
+            parameters={"SingleParamCfn": "/path/to/single/param",},
+            region_name="us-west-1",
+        )
+
+        stack.resource_map.resolved_parameters["SingleParamCfn"].should.equal("string")
+        stack.resource_map.resolved_parameters["ListParamCfn"].should.equal(
+            ["comma", "separated", "string"]
+        )