Fix missing properties when ecs:TaskDefinition created via CloudFormation (#3378)

There's a larger problem here that needs a more generalized solution,
but this solves the immediate issue with a minimum amount of code.

Closes #3171

moto/core/utils.py

@@ -57,6 +57,11 @@ def underscores_to_camelcase(argument):
     return result
 
 
+def pascal_to_camelcase(argument):
+    """Converts a PascalCase param to the camelCase equivalent"""
+    return argument[0].lower() + argument[1:]
+
+
 def method_names_from_class(clazz):
     # On Python 2, methods are different from functions, and the `inspect`
     # predicates distinguish between them. On Python 3, methods are just
@@ -367,3 +372,30 @@ def tags_from_cloudformation_tags_list(tags_list):
         tags[key] = value
 
     return tags
+
+
+def remap_nested_keys(root, key_transform):
+    """This remap ("recursive map") function is used to traverse and
+    transform the dictionary keys of arbitrarily nested structures.
+    List comprehensions do not recurse, making it tedious to apply
+    transforms to all keys in a tree-like structure.
+
+    A common issue for `moto` is changing the casing of dict keys:
+
+    >>> remap_nested_keys({'KeyName': 'Value'}, camelcase_to_underscores)
+    {'key_name': 'Value'}
+
+    Args:
+        root: The target data to traverse. Supports iterables like
+            :class:`list`, :class:`tuple`, and :class:`dict`.
+        key_transform (callable): This function is called on every
+            dictionary key found in *root*.
+    """
+    if isinstance(root, (list, tuple)):
+        return [remap_nested_keys(item, key_transform) for item in root]
+    if isinstance(root, dict):
+        return {
+            key_transform(k): remap_nested_keys(v, key_transform)
+            for k, v in six.iteritems(root)
+        }
+    return root

moto/ecs/models.py

@@ -11,7 +11,7 @@ from boto3 import Session
 
 from moto.core import BaseBackend, BaseModel, CloudFormationModel
 from moto.core.exceptions import JsonRESTError
-from moto.core.utils import unix_time
+from moto.core.utils import unix_time, pascal_to_camelcase, remap_nested_keys
 from moto.ec2 import ec2_backends
 from .exceptions import (
     ServiceNotFoundException,
@@ -174,8 +174,10 @@ class TaskDefinition(BaseObject, CloudFormationModel):
         family = properties.get(
             "Family", "task-definition-{0}".format(int(random() * 10 ** 6))
         )
-        container_definitions = properties["ContainerDefinitions"]
-        volumes = properties.get("Volumes")
+        container_definitions = remap_nested_keys(
+            properties.get("ContainerDefinitions", []), pascal_to_camelcase
+        )
+        volumes = remap_nested_keys(properties.get("Volumes", []), pascal_to_camelcase)
 
         ecs_backend = ecs_backends[region_name]
         return ecs_backend.register_task_definition(

tests/test_ecs/test_ecs_cloudformation.py

@@ -2,6 +2,8 @@ import boto3
 import json
 from copy import deepcopy
 from moto import mock_cloudformation, mock_ecs
+from moto.core.utils import pascal_to_camelcase, remap_nested_keys
+import sure  # noqa
 
 
 @mock_ecs
@@ -231,9 +233,16 @@ def test_create_task_definition_through_cloudformation():
                             "Cpu": "200",
                             "Memory": "500",
                             "Essential": "true",
+                            "PortMappings": [
+                                {
+                                    "ContainerPort": 123,
+                                    "HostPort": 123,
+                                    "Protocol": "tcp",
+                                },
+                            ],
                         }
                     ],
-                    "Volumes": [],
+                    "Volumes": [{"Name": "ecs-vol"}],
                 },
             }
         },
@@ -252,3 +261,14 @@ def test_create_task_definition_through_cloudformation():
         StackName=stack_name, LogicalResourceId="testTaskDefinition"
     )["StackResourceDetail"]
     task_definition_details["PhysicalResourceId"].should.equal(task_definition_arn)
+
+    task_definition = ecs_conn.describe_task_definition(
+        taskDefinition=task_definition_arn
+    ).get("taskDefinition")
+    expected_properties = remap_nested_keys(
+        template["Resources"]["testTaskDefinition"]["Properties"], pascal_to_camelcase
+    )
+    task_definition["volumes"].should.equal(expected_properties["volumes"])
+    task_definition["containerDefinitions"].should.equal(
+        expected_properties["containerDefinitions"]
+    )