Ensure that global containers are not scaled

Signed-off-by: Felipe Ruhland <felipe.ruhland@gmail.com>

docker/models/services.py

 import copy
-from docker.errors import create_unexpected_kwargs_error
+from docker.errors import create_unexpected_kwargs_error, InvalidArgument
 from docker.types import TaskTemplate, ContainerSpec, ServiceMode
 from .resource import Model, Collection
 
@@ -116,6 +116,9 @@ class Service(Model):
             ``True``if successful.
         """
 
+        if not self.attrs['Spec']['Mode'].get('Global'):
+            raise InvalidArgument('Cannot scale a global container')
+
         service_mode = ServiceMode('replicated', replicas)
         return self.client.api.update_service(self.id, self.version,
                                               service_mode,

tests/integration/models_services_test.py

@@ -4,6 +4,8 @@ import docker
 
 from .. import helpers
 from .base import TEST_API_VERSION
+from docker.errors import InvalidArgument
+from docker.models.services import ServiceMode
 
 
 class ServiceTest(unittest.TestCase):
@@ -225,6 +227,28 @@ class ServiceTest(unittest.TestCase):
         spec = service.attrs['Spec']['TaskTemplate']['ContainerSpec']
         assert spec.get('Command') == ['sleep', '300']
 
+    def test_scale_method_global_service(self):
+        client = docker.from_env(version=TEST_API_VERSION)
+        mode = ServiceMode('global')
+        service = client.services.create(
+            name=helpers.random_name(),
+            image="alpine",
+            command="sleep 300",
+            mode=mode
+        )
+        tasks = []
+        while len(tasks) == 0:
+            tasks = service.tasks()
+        assert len(tasks) == 1
+        with self.assertRaises(InvalidArgument,
+                               msg='Cannot scale a global container'):
+            service.scale(2)
+
+        assert len(tasks) == 1
+        service.reload()
+        spec = service.attrs['Spec']['TaskTemplate']['ContainerSpec']
+        assert spec.get('Command') == ['sleep', '300']
+
     @helpers.requires_api_version('1.25')
     def test_restart_service(self):
         client = docker.from_env(version=TEST_API_VERSION)