Add --exclude-container-label argument to dcgc

Add an argument to dcgc that allows dcgc to ignore removing a container
and its child images based on the container's label

README.rst

@@ -92,6 +92,30 @@ You also can use basic pattern matching to exclude images with generic tags.
     user/repositoryB:?.?
     user/repositoryC-*:tag
 
+
+Prevent containers and associated images from being removed
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+``dcgc`` also supports a container exclude list based on labels.  If there are
+stopped containers that you'd like to keep, then you can check the labels to
+prevent them from being removed.
+
+::
+
+    --exclude-container-label
+        Never remove containers that have the label key=value. =value can be
+        omitted and in that case only the key is checked. May be specified
+        more than once.
+
+You also can use basic pattern matching to exclude generic labels.
+
+.. code::
+
+    foo*
+    com.docker.compose.project=test*
+    com.docker*=*bar*
+
+
 dcstop
 ------
 

docker_custodian/docker_gc.py

@@ -23,14 +23,26 @@ log = logging.getLogger(__name__)
 YEAR_ZERO = "0001-01-01T00:00:00Z"
 
 
-def cleanup_containers(client, max_container_age, dry_run):
+def cleanup_containers(
+    client,
+    max_container_age,
+    dry_run,
+    exclude_container_labels,
+):
     all_containers = get_all_containers(client)
-
-    for container_summary in reversed(all_containers):
-        container = api_call(client.inspect_container,
-                             container=container_summary['Id'])
-        if not container or not should_remove_container(container,
-                                                        max_container_age):
+    filtered_containers = filter_excluded_containers(
+        all_containers,
+        exclude_container_labels,
+    )
+    for container_summary in reversed(list(filtered_containers)):
+        container = api_call(
+            client.inspect_container,
+            container=container_summary['Id'],
+        )
+        if not container or not should_remove_container(
+            container,
+            max_container_age,
+        ):
             continue
 
         log.info("Removing container %s %s %s" % (
@@ -39,8 +51,43 @@ def cleanup_containers(client, max_container_age, dry_run):
             container['State']['FinishedAt']))
 
         if not dry_run:
-            api_call(client.remove_container, container=container['Id'],
-                     v=True)
+            api_call(
+                client.remove_container,
+                container=container['Id'],
+                v=True,
+            )
+
+
+def filter_excluded_containers(containers, exclude_container_labels):
+    def include_container(container):
+        if exclude_container_labels and should_exclude_container_with_labels(
+            container,
+            exclude_container_labels,
+        ):
+            return False
+        return True
+    return filter(include_container, containers)
+
+
+def should_exclude_container_with_labels(container, exclude_container_labels):
+    for exclude_container_label in exclude_container_labels:
+        split_exclude_label = exclude_container_label.split('=', 1)
+        if len(split_exclude_label) == 2:
+            exclude_key, exclude_value = split_exclude_label
+            matching_keys = fnmatch.filter(
+                container['Labels'].keys(), exclude_key
+            )
+            label_values_to_check = [
+                container['Labels'][matching_key]
+                for matching_key in matching_keys
+            ]
+            if fnmatch.filter(label_values_to_check, exclude_value):
+                return True
+        else:
+            exclude_key = split_exclude_label[0]
+            if fnmatch.filter(container['Labels'].keys(), exclude_key):
+                return True
+    return False
 
 
 def should_remove_container(container, min_date):
@@ -226,7 +273,12 @@ def main():
                               **kwargs_from_env())
 
     if args.max_container_age:
-        cleanup_containers(client, args.max_container_age, args.dry_run)
+        cleanup_containers(
+            client,
+            args.max_container_age,
+            args.dry_run,
+            args.exclude_container_label,
+        )
 
     if args.max_image_age:
         exclude_set = build_exclude_set(
@@ -271,6 +323,10 @@ def get_args(args=None):
         type=argparse.FileType('r'),
         help="Path to a file which contains a list of images to exclude, one "
              "image tag per line.")
+    parser.add_argument(
+        '--exclude-container-label',
+        action='append',
+        help="Never remove containers with this label key or label key=value")
 
     return parser.parse_args(args=args)
 

tests/docker_gc_test.py

@@ -51,24 +51,47 @@ def test_cleanup_containers(mock_client, now):
             'Name': 'one',
             'State': {
                 'Running': False,
-                'FinishedAt': '2014-01-01T01:01:01Z'
-            }
+                'FinishedAt': '2014-01-01T01:01:01Z',
+            },
         },
         {
             'Id': 'abbb',
             'Name': 'two',
             'State': {
                 'Running': True,
-                'FinishedAt': '2014-01-01T01:01:01Z'
-            }
-        }
+                'FinishedAt': '2014-01-01T01:01:01Z',
+            },
+        },
     ]
     mock_client.inspect_container.side_effect = iter(mock_containers)
-    docker_gc.cleanup_containers(mock_client, max_container_age, False)
+    docker_gc.cleanup_containers(mock_client, max_container_age, False, None)
     mock_client.remove_container.assert_called_once_with(container='abcd',
                                                          v=True)
 
 
+def test_filter_excluded_containers():
+    mock_containers = [
+        {'Labels': {'toot': ''}},
+        {'Labels': {'too': 'lol'}},
+        {'Labels': {'toots': 'lol'}},
+        {'Labels': {'foo': 'bar'}},
+    ]
+    result = docker_gc.filter_excluded_containers(mock_containers, None)
+    assert mock_containers == list(result)
+    exclude_labels = ['too', 'foo']
+    result = docker_gc.filter_excluded_containers(
+        mock_containers,
+        exclude_labels,
+    )
+    assert [mock_containers[0], mock_containers[2]] == list(result)
+    exclude_labels = ['too*=lol']
+    result = docker_gc.filter_excluded_containers(
+        mock_containers,
+        exclude_labels,
+    )
+    assert [mock_containers[0], mock_containers[3]] == list(result)
+
+
 def test_cleanup_images(mock_client, now):
     max_image_age = now
     mock_client.images.return_value = images = [