Add wsgi module to blazar

Changes in python packaging tooling mean that the wsgi_scripts
functionality via PBR may not longer function.

This patch switches blazar from using the PBR wsgi_scripts method to
using a new wsgi module that provides the same behavior as the generated
wsgi scripts provided.

A related devstack patch enables devstack to setup uWSGI to use the new
module path instead of the generated wsgi scripts.

For more details see the proposed OpenStack goal [1].

[1] https://review.opendev.org/c/openstack/governance/+/902807

Change-Id: Ib16d5d1ea5d7416d7b1f026f771d6c2b77657970

blazar/wsgi/api.py

@@ -0,0 +1,24 @@
+# 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 the Blazar API."""
+
+import threading
+
+from blazar.api import wsgi_app
+
+application = None
+
+lock = threading.Lock()
+with lock:
+    if application is None:
+        application = wsgi_app.init_app()

devstack/plugin.sh

@@ -80,7 +80,7 @@ function configure_blazar {
     iniadd $NOVA_CONF filter_scheduler available_filters "blazarnova.scheduler.filters.blazar_filter.BlazarFilter"
 
     if [[ "$BLAZAR_USE_MOD_WSGI" == "True" ]]; then
-        write_uwsgi_config "$BLAZAR_UWSGI_CONF" "$BLAZAR_UWSGI" "/reservation"
+        write_uwsgi_config "$BLAZAR_UWSGI_CONF" "$BLAZAR_UWSGI" "/reservation" "" "blazar"
     fi
 
     # Database

devstack/settings

@@ -31,7 +31,7 @@ BLAZAR_DASHBOARD_DIR=$DEST/blazar-dashboard
 # wsgi deployment
 BLAZAR_USE_MOD_WSGI=${BLAZAR_USE_MOD_WSGI:-True}
 BLAZAR_BIN_DIR=$(get_python_exec_prefix)
-BLAZAR_UWSGI=$BLAZAR_BIN_DIR/blazar-api-wsgi
+BLAZAR_UWSGI=blazar.wsgi.api:application
 BLAZAR_UWSGI_CONF=$BLAZAR_CONF_DIR/blazar-api-uwsgi.ini
 
 BLAZAR_SERVICE_HOST=${BLAZAR_SERVICE_HOST:-$SERVICE_HOST}

releasenotes/notes/remove-wsgi-scripts-1e2011c1d40df1c7.yaml

@@ -0,0 +1,29 @@
+---
+features:
+  - |
+    A new module, ``blazar.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/blazar-api-wsgi
+
+    You can now use:
+
+    .. code-block:: ini
+
+        [uwsgi]
+        module = blazar.wsgi.api:application
+
+    This also simplifies deployment with other WSGI servers that expect module
+    paths such as gunicorn.
+upgrade:
+  - |
+    The WSGI script ``blazar-api-wsgi`` has been removed. Deployment tooling
+    should instead reference the Python module path for the wsgi module in
+    Blazar, ``blazar.wsgi.api:application`` if their chosen WSGI server
+    supports this (gunicorn, uWSGI, etc.) or implement a .wsgi script
+    themselves if not (mod_wsgi).