From 79e47fd98ff005848f1592a62b18a485e199ebba Mon Sep 17 00:00:00 2001
From: Kyle Decot <kyle@joinroot.com>
Date: Wed, 27 Feb 2019 15:05:58 -0500
Subject: [PATCH 1/2] Returns an empty list when the cluster does not exist

---
 moto/ecs/models.py | 3 ---
 1 file changed, 3 deletions(-)

diff --git a/moto/ecs/models.py b/moto/ecs/models.py
index 4a6737ceb..13de67268 100644
--- a/moto/ecs/models.py
+++ b/moto/ecs/models.py
@@ -428,9 +428,6 @@ class EC2ContainerServiceBackend(BaseBackend):
                 if cluster_name in self.clusters:
                     list_clusters.append(
                         self.clusters[cluster_name].response_object)
-                else:
-                    raise Exception(
-                        "{0} is not a cluster".format(cluster_name))
         return list_clusters
 
     def delete_cluster(self, cluster_str):

From d181897ec91f3776a44b21d8307b72d407c044c0 Mon Sep 17 00:00:00 2001
From: Nick Venenga <nick.venenga@joinroot.com>
Date: Fri, 22 Mar 2019 12:08:02 -0400
Subject: [PATCH 2/2] Add proper failure response to describe_clusters

---
 moto/ecs/models.py               | 19 ++++++++++++++++++-
 moto/ecs/responses.py            |  4 ++--
 tests/test_ecs/test_ecs_boto3.py |  9 +++++++++
 3 files changed, 29 insertions(+), 3 deletions(-)

diff --git a/moto/ecs/models.py b/moto/ecs/models.py
index 13de67268..c9fdb9808 100644
--- a/moto/ecs/models.py
+++ b/moto/ecs/models.py
@@ -358,6 +358,20 @@ class ContainerInstance(BaseObject):
         return formatted_attr
 
 
+class ClusterFailure(BaseObject):
+    def __init__(self, reason, cluster_name):
+        self.reason = reason
+        self.arn = "arn:aws:ecs:us-east-1:012345678910:cluster/{0}".format(
+            cluster_name)
+
+    @property
+    def response_object(self):
+        response_object = self.gen_response_object()
+        response_object['reason'] = self.reason
+        response_object['arn'] = self.arn
+        return response_object
+
+
 class ContainerInstanceFailure(BaseObject):
 
     def __init__(self, reason, container_instance_id):
@@ -419,6 +433,7 @@ class EC2ContainerServiceBackend(BaseBackend):
 
     def describe_clusters(self, list_clusters_name=None):
         list_clusters = []
+        failures = []
         if list_clusters_name is None:
             if 'default' in self.clusters:
                 list_clusters.append(self.clusters['default'].response_object)
@@ -428,7 +443,9 @@ class EC2ContainerServiceBackend(BaseBackend):
                 if cluster_name in self.clusters:
                     list_clusters.append(
                         self.clusters[cluster_name].response_object)
-        return list_clusters
+                else:
+                    failures.append(ClusterFailure('MISSING', cluster_name))
+        return list_clusters, failures
 
     def delete_cluster(self, cluster_str):
         cluster_name = cluster_str.split('/')[-1]
diff --git a/moto/ecs/responses.py b/moto/ecs/responses.py
index e0bfefc02..964ef59d2 100644
--- a/moto/ecs/responses.py
+++ b/moto/ecs/responses.py
@@ -45,10 +45,10 @@ class EC2ContainerServiceResponse(BaseResponse):
 
     def describe_clusters(self):
         list_clusters_name = self._get_param('clusters')
-        clusters = self.ecs_backend.describe_clusters(list_clusters_name)
+        clusters, failures = self.ecs_backend.describe_clusters(list_clusters_name)
         return json.dumps({
             'clusters': clusters,
-            'failures': []
+            'failures': [cluster.response_object for cluster in failures]
         })
 
     def delete_cluster(self):
diff --git a/tests/test_ecs/test_ecs_boto3.py b/tests/test_ecs/test_ecs_boto3.py
index a0d470935..3bf25b8fc 100644
--- a/tests/test_ecs/test_ecs_boto3.py
+++ b/tests/test_ecs/test_ecs_boto3.py
@@ -47,6 +47,15 @@ def test_list_clusters():
         'arn:aws:ecs:us-east-1:012345678910:cluster/test_cluster1')
 
 
+@mock_ecs
+def test_describe_clusters():
+    client = boto3.client('ecs', region_name='us-east-1')
+    response = client.describe_clusters(clusters=["some-cluster"])
+    response['failures'].should.contain({
+        'arn': 'arn:aws:ecs:us-east-1:012345678910:cluster/some-cluster',
+        'reason': 'MISSING'
+    })
+
 @mock_ecs
 def test_delete_cluster():
     client = boto3.client('ecs', region_name='us-east-1')