Support reload configuration on SIGHUP

This adds signal handler to reload mutable configuration options
on SIGHUP.

It has to be done manually, because ironic-inspector doesn't use
oslo.service.

Change-Id: I38955fe9dbfd339df2a10dcbb55e996bf515034a
Story: #1585595
Task: #12543

ironic_inspector/test/unit/test_wsgi_service.py

@@ -422,3 +422,20 @@ class TestCreateSSLContext(test_base.BaseTest):
         self.assertEqual(mock_context, con)
         mock_context.load_cert_chain.assert_called_once_with(cert_path,
                                                              key_path)
+
+
+class TestWSGIServiceOnSigHup(BaseWSGITest):
+    def setUp(self):
+        super(TestWSGIServiceOnSigHup, self).setUp()
+        self.mock_spawn = self.useFixture(fixtures.MockPatchObject(
+            wsgi_service.eventlet, 'spawn')).mock
+        self.mock_mutate_conf = self.useFixture(fixtures.MockPatchObject(
+            wsgi_service.CONF, 'mutate_config_files')).mock
+
+    def test_on_sighup(self):
+        self.service._handle_sighup()
+        self.mock_spawn.assert_called_once_with(self.service._handle_sighup_bg)
+
+    def test_on_sighup_bg(self):
+        self.service._handle_sighup_bg()
+        self.mock_mutate_conf.assert_called_once_with()

ironic_inspector/wsgi_service.py

@@ -10,6 +10,7 @@
 # License for the specific language governing permissions and limitations
 # under the License.
 
+import signal
 import ssl
 import sys
 import traceback as traceback_mod
@@ -41,6 +42,7 @@ class WSGIService(object):
         self.app = app.app
         self._periodics_worker = None
         self._shutting_down = semaphore.Semaphore()
+        signal.signal(signal.SIGHUP, self._handle_sighup)
 
     def _init_middleware(self):
         """Initialize WSGI middleware.
@@ -189,6 +191,13 @@ class WSGIService(object):
         else:
             self.shutdown()
 
+    def _handle_sighup_bg(self, *args):
+        """Reload config on SIGHUP."""
+        CONF.mutate_config_files()
+
+    def _handle_sighup(self, *args):
+        eventlet.spawn(self._handle_sighup_bg, *args)
+
 
 def periodic_clean_up():  # pragma: no cover
     try:

releasenotes/notes/sighup-support-e6eaec034d963108.yaml

@@ -0,0 +1,11 @@
+---
+features:
+  - |
+    Issuing a SIGHUP to the ironic-inspector service will cause the service to
+    reload and use any changed values for *mutable* configuration options.
+
+    Mutable configuration options are indicated as such in the `sample
+    configuration file <https://docs.openstack.org/ironic-inspector/latest/configuration/sample-config.html>`_
+    by ``Note: This option can be changed without restarting``.
+
+    A warning is logged for any changes to immutable configuration options.