systemd: auto-shutdown old master post USR2 re-exec

Author: pajod

docs/source/signals.rst

@@ -117,3 +117,9 @@ running::
     20859 benoitc   20   0 55748  11m 1500 S   0.0  0.1   0:00.02 gunicorn: worker [test:app]
     20860 benoitc   20   0 55748  11m 1500 S   0.0  0.1   0:00.02 gunicorn: worker [test:app]
     20861 benoitc   20   0 55748  11m 1500 S   0.0  0.1   0:00.01 gunicorn: worker [test:app]
+
+If no pidfile is available (``kill -TERM $(cat /var/run/gunicorn.pid)``) then killing
+the *oldest* process (``pkill --oldest -TERM -f "gunicorn: master "``) should suffice.
+
+When running via systemd socket activation, Gunicorn will *automatically* issue the graceful
+shutdown of the old master, as part of starting up the new one.

gunicorn/arbiter.py

@@ -173,6 +173,8 @@ def start(self):
 
         self.cfg.when_ready(self)
 
+        # systemd: not yet shutting down old master here (wait for workers)
+
     def init_signals(self):
         """\
         Initialize master signal handling. Most of the signals
@@ -339,6 +341,12 @@ def maybe_promote_master(self):
             # MAINPID does not change here, it was already set on fork
             systemd.sd_notify("READY=1\nMAINPID=%d\nSTATUS=Gunicorn arbiter promoted" % (os.getpid(), ), self.log)
 
+        elif self.systemd and len(self.WORKERS) >= 1:
+            # still attached to old master, but we are ready to take over
+            #  this automates `kill -TERM $(cat /var/run/gunicorn.pid)`
+            self.log.debug("systemd managed: shutting down old master %d after re-exec", self.master_pid)
+            os.kill(self.master_pid, signal.SIGTERM)
+
     def wakeup(self):
         """\
         Wake up the arbiter by writing to the PIPE