CF: Raise ValidationError on bad resource id (#4186)

moto/cloudformation/responses.py

@@ -230,11 +230,18 @@ class CloudFormationResponse(BaseResponse):
         stack = self.cloudformation_backend.get_stack(stack_name)
         logical_resource_id = self._get_param("LogicalResourceId")
 
+        resource = None
         for stack_resource in stack.stack_resources:
             if stack_resource.logical_resource_id == logical_resource_id:
                 resource = stack_resource
                 break
 
+        if not resource:
+            message = "Resource {0} does not exist for stack {1}".format(
+                logical_resource_id, stack_name
+            )
+            raise ValidationError(stack_name, message)
+
         template = self.response_template(DESCRIBE_STACK_RESOURCE_RESPONSE_TEMPLATE)
         return template.render(stack=stack, resource=resource)
 

tests/test_cloudformation/test_cloudformation_stack_crud_boto3.py

@@ -6,7 +6,7 @@ from datetime import datetime, timedelta
 import pytz
 
 import boto3
-from botocore.exceptions import ClientError
+from botocore.exceptions import ClientError, ValidationError
 import sure  # noqa
 
 import pytest
@@ -1139,6 +1139,37 @@ def test_describe_stack_pagination():
     assert "NextToken" not in resp2.keys()
 
 
+@mock_cloudformation
+def test_describe_stack_resource():
+    cf_conn = boto3.client("cloudformation", region_name="us-east-1")
+    cf_conn.create_stack(StackName="test_stack", TemplateBody=dummy_template_json)
+
+    stack = cf_conn.describe_stacks(StackName="test_stack")["Stacks"][0]
+
+    response = cf_conn.describe_stack_resource(
+        StackName=stack["StackName"], LogicalResourceId="EC2Instance1"
+    )
+
+    resource = response["StackResourceDetail"]
+    resource["LogicalResourceId"].should.equal("EC2Instance1")
+    resource["ResourceStatus"].should.equal("CREATE_COMPLETE")
+    resource["ResourceType"].should.equal("AWS::EC2::Instance")
+    resource["StackId"].should.equal(stack["StackId"])
+
+
+@mock_cloudformation
+def test_describe_stack_resource_when_resource_does_not_exist():
+    cf_conn = boto3.client("cloudformation", region_name="us-east-1")
+    cf_conn.create_stack(StackName="test_stack", TemplateBody=dummy_template_json)
+
+    stack = cf_conn.describe_stacks(StackName="test_stack")["Stacks"][0]
+
+    with pytest.raises(ClientError, match="does not exist for stack"):
+        cf_conn.describe_stack_resource(
+            StackName=stack["StackName"], LogicalResourceId="DoesNotExist"
+        )
+
+
 @mock_cloudformation
 def test_describe_stack_resources():
     cf_conn = boto3.client("cloudformation", region_name="us-east-1")