Add placement.wsgi.api module

This allows deployment tooling to easily switch from passing a binary
path to passing a Python module path.

Change-Id: Ib8fc2d917d1427b369a299527ed4b68577951a04
Signed-off-by: Stephen Finucane <stephenfin@redhat.com>

placement/wsgi/api.py

@@ -0,0 +1,22 @@
+#    Licensed under the Apache License, Version 2.0 (the "License"); you may
+#    not use this file except in compliance with the License. You may obtain
+#    a copy of the License at
+#
+#         http://www.apache.org/licenses/LICENSE-2.0
+#
+#    Unless required by applicable law or agreed to in writing, software
+#    distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+#    WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+#    License for the specific language governing permissions and limitations
+#    under the License.
+"""WSGI application entry-point for Placement API."""
+
+import threading
+
+from placement import wsgi
+
+
+application = None
+with threading.Lock():
+    if application is None:
+        application = wsgi.init_application()

releasenotes/notes/add-placment-wsgi-module-ae42938ebe0258cb.yaml

@@ -0,0 +1,22 @@
+---
+features:
+  - |
+    A new module, ``placement.wsgi``, has been added as a place to gather WSGI
+    ``application`` objects. This is intended to ease deployment by providing
+    a consistent location for these objects. For example, if using uWSGI then
+    instead of:
+
+    .. code-block:: ini
+
+        [uwsgi]
+        wsgi-file = /bin/placement-api
+
+    You can now use:
+
+    .. code-block:: ini
+
+        [uwsgi]
+        module = placement.wsgi.api:application
+
+    This also simplifies deployment with other WSGI servers that expect module
+    paths such as gunicorn.