Improve placement handling in DockerClient.services.create

Signed-off-by: Joffrey F <joffrey@docker.com>

docker/models/services.py

 import copy
 from docker.errors import create_unexpected_kwargs_error, InvalidArgument
-from docker.types import TaskTemplate, ContainerSpec, ServiceMode
+from docker.types import TaskTemplate, ContainerSpec, Placement, ServiceMode
 from .resource import Model, Collection
 
 
@@ -153,6 +153,9 @@ class ServiceCollection(Collection):
             command (list of str or str): Command to run.
             args (list of str): Arguments to the command.
             constraints (list of str): Placement constraints.
+            preferences (list of str): Placement preferences.
+            platforms (list of tuple): A list of platforms constraints
+                expressed as ``(arch, os)`` tuples
             container_labels (dict): Labels to apply to the container.
             endpoint_spec (EndpointSpec): Properties that can be configured to
                 access and load balance a service. Default: ``None``.
@@ -302,6 +305,12 @@ CREATE_SERVICE_KWARGS = [
     'endpoint_spec',
 ]
 
+PLACEMENT_KWARGS = [
+    'constraints',
+    'preferences',
+    'platforms',
+]
+
 
 def _get_create_service_kwargs(func_name, kwargs):
     # Copy over things which can be copied directly
@@ -322,13 +331,10 @@ def _get_create_service_kwargs(func_name, kwargs):
         container_spec_kwargs['labels'] = kwargs.pop('container_labels')
 
     placement = {}
-
-    if 'constraints' in kwargs:
-        placement['Constraints'] = kwargs.pop('constraints')
-
-    if 'preferences' in kwargs:
-        placement['Preferences'] = kwargs.pop('preferences')
-
+    for key in copy.copy(kwargs):
+        if key in PLACEMENT_KWARGS:
+            placement[key] = kwargs.pop(key)
+    placement = Placement(**placement)
     task_template_kwargs['placement'] = placement
 
     if 'log_driver' in kwargs:

tests/unit/models_services_test.py

@@ -26,6 +26,8 @@ class CreateServiceKwargsTest(unittest.TestCase):
             'mounts': [{'some': 'mounts'}],
             'stop_grace_period': 5,
             'constraints': ['foo=bar'],
+            'preferences': ['bar=baz'],
+            'platforms': [('x86_64', 'linux')],
         })
 
         task_template = kwargs.pop('task_template')
@@ -41,7 +43,11 @@ class CreateServiceKwargsTest(unittest.TestCase):
             'ContainerSpec', 'Resources', 'RestartPolicy', 'Placement',
             'LogDriver', 'Networks'
         ])
-        assert task_template['Placement'] == {'Constraints': ['foo=bar']}
+        assert task_template['Placement'] == {
+            'Constraints': ['foo=bar'],
+            'Preferences': ['bar=baz'],
+            'Platforms': [{'Architecture': 'x86_64', 'OS': 'linux'}],
+        }
         assert task_template['LogDriver'] == {
             'Name': 'logdriver',
             'Options': {'foo': 'bar'}