Add on_stopping hook to set anything before master is killed

docs/source/settings.rst

@@ -725,6 +725,20 @@ Called to recycle workers during a reload via SIGHUP.
 
 The callable needs to accept a single instance variable for the Arbiter.
 
+``on_stopping``
+~~~~~~~~~~~~~~~
+
+**Default:** 
+
+.. code-block:: python
+
+        def on_stopping(server):
+            pass
+
+Called just before the master process is stopped.
+
+The callable needs to accept a single instance variable for the Arbiter.
+
 .. _when-ready:
 
 ``when_ready``

gunicorn/arbiter.py

@@ -377,6 +377,8 @@ def stop(self, graceful=True):
         :attr graceful: boolean, If True (the default) workers will be
         killed gracefully  (ie. trying to wait for the current connection)
         """
+        self.cfg.on_stopping(self)
+
         unlink = (
             self.reexec_pid == self.master_pid == 0
             and not self.systemd

gunicorn/config.py

@@ -1767,6 +1767,22 @@ def on_reload(server):
         """
 
 
+class OnStopping(Setting):
+    name = "on_stopping"
+    section = "Server Hooks"
+    validator = validate_callable(1)
+    type = callable
+
+    def on_stopping(server):
+        pass
+    default = staticmethod(on_stopping)
+    desc = """\
+        Called just before the master process is stopped.
+
+        The callable needs to accept a single instance variable for the Arbiter.
+        """
+
+
 class WhenReady(Setting):
     name = "when_ready"
     section = "Server Hooks"