Make PID availabe as formatstring in backdoor path

When multiple processes are spawned with the same configuration
each process has the same backdoor_socket path configured and
only the first process able to bind to the socket can later be
accessed via the backdoor. To give each process a unique socket path
we now expose the PID of the process as a format string argument,
which can then be used like this:

backdoor_socket = /var/lib/neutron/backdoor-{pid}

Change-Id: I3f86f4867eb0cd5010abadf68620aa3450d3e64d

oslo_service/_options.py

@@ -31,7 +31,8 @@ eventlet_backdoor_opts = [
                     " option is mutually exclusive with 'backdoor_port' in"
                     " that only one should be provided. If both are provided"
                     " then the existence of this option overrides the usage of"
-                    " that option.")
+                    " that option. Inside the path {pid} will be replaced with"
+                    " the PID of the current process.")
 ]
 
 periodic_opts = [

oslo_service/eventlet_backdoor.py

@@ -214,8 +214,16 @@ def _initialize_if_enabled(conf):
         # listen().  In any case, pull the port number out here.
         where_running = sock.getsockname()[1]
     else:
-        sock = _try_open_unix_domain_socket(conf.backdoor_socket)
-        where_running = conf.backdoor_socket
+        try:
+            backdoor_socket_path = conf.backdoor_socket.format(pid=os.getpid())
+        except (KeyError, IndexError, ValueError) as e:
+            backdoor_socket_path = conf.backdoor_socket
+            LOG.warning("Could not apply format string to eventlet "
+                        "backdoor socket path ({}) - continuing with "
+                        "unformatted path"
+                        "".format(e))
+        sock = _try_open_unix_domain_socket(backdoor_socket_path)
+        where_running = backdoor_socket_path
 
     # NOTE(johannes): The standard sys.displayhook will print the value of
     # the last expression and set it to __builtin__._, which overwrites

oslo_service/tests/test_eventlet_backdoor.py

@@ -38,6 +38,30 @@ class BackdoorSocketPathTest(base.ServiceBaseTestCase):
         path = eventlet_backdoor.initialize_if_enabled(self.conf)
         self.assertEqual("/tmp/my_special_socket", path)
 
+    @mock.patch.object(eventlet, 'spawn')
+    @mock.patch.object(eventlet, 'listen')
+    def test_backdoor_path_with_format_string(self, listen_mock, spawn_mock):
+        self.config(backdoor_socket="/tmp/my_special_socket-{pid}")
+        listen_mock.side_effect = mock.Mock()
+        path = eventlet_backdoor.initialize_if_enabled(self.conf)
+        expected_path = "/tmp/my_special_socket-{}".format(os.getpid())
+        self.assertEqual(expected_path, path)
+
+    @mock.patch.object(eventlet, 'spawn')
+    @mock.patch.object(eventlet, 'listen')
+    def test_backdoor_path_with_broken_format_string(self, listen_mock,
+                                                     spawn_mock):
+        broken_socket_paths = [
+            "/tmp/my_special_socket-{}",
+            "/tmp/my_special_socket-{broken",
+            "/tmp/my_special_socket-{broken}",
+        ]
+        for socket_path in broken_socket_paths:
+            self.config(backdoor_socket=socket_path)
+            listen_mock.side_effect = mock.Mock()
+            path = eventlet_backdoor.initialize_if_enabled(self.conf)
+            self.assertEqual(socket_path, path)
+
     @mock.patch.object(os, 'unlink')
     @mock.patch.object(eventlet, 'spawn')
     @mock.patch.object(eventlet, 'listen')

releasenotes/notes/support-pid-in-eventlet-backdoor-socket-path-1863eaad1dd08556.yaml

@@ -0,0 +1,8 @@
+---
+features:
+  - |
+    The config option backdoor_socket_path now is a format string that
+    supports {pid}, which will be replaced with the PID of the current
+    process. This makes the eventlet backdoor accessible when spawning
+    multiple processes with the same backdoor_socket_path inside the
+    configuration.