Use pidfile for services

Currently when we start the service we use podman start -a when we start
the service so systemd monitors that process for the service. The
problem is that this leaves podman start processes around which have a
bunch of threads and is attached to the STDOUT/STDIN.  Rather than
leaving this start process around, let's switch to a forking type in
system and specify a conmon pidfile for monitoring the container.  This
removes 500+ threads from the system.

Change-Id: Ie9225ce484b94b7fd59036168aaae58f25f1589d
Co-Authored-By: Emilien Macchi <emilien@redhat.com>

paunch/builder/podman.py

@@ -24,6 +24,10 @@ class PodmanBuilder(base.BaseBuilder):
 
     def container_run_args(self, cmd, container):
         cconfig = self.config[container]
+
+        # write out a pid file so we can restart the container via systemd
+        cmd.append('--conmon-pidfile=/var/run/{}.pid'.format(container))
+
         if cconfig.get('detach', True):
             cmd.append('--detach=true')
 

paunch/tests/test_builder_podman.py

@@ -45,6 +45,7 @@ class TestPodmanBuilder(base.TestBaseBuilder):
         builder.container_run_args(cmd, 'one')
         self.assertEqual(
             ['podman', 'run', '--name', 'one',
+             '--conmon-pidfile=/var/run/one.pid',
              '--detach=true', '--env-file=/tmp/foo.env',
              '--net=host', '--ipc=host', '--pid=container:bar',
              '--uts=host', '--privileged=true', '--user=bar',

paunch/tests/test_utils_systemd.py

@@ -38,6 +38,7 @@ class TestUtilsSystemd(base.TestCase):
         self.assertIn('Wants=something.service', unit)
         self.assertIn('Restart=always', unit)
         self.assertIn('ExecStop=/usr/bin/podman stop -t 15 my_app', unit)
+        self.assertIn('PIDFile=/var/run/my_app.pid', unit)
         mock_chmod.assert_has_calls([mock.call(sysd_unit_f, 420)])
 
         mock_subprocess_check_call.assert_has_calls([

paunch/utils/systemd.py

@@ -80,9 +80,11 @@ After=paunch-container-shutdown.service
 Wants=%(wants)s
 [Service]
 Restart=%(restart)s
-ExecStart=/usr/bin/podman start -a %(name)s
+ExecStart=/usr/bin/podman start %(name)s
 ExecStop=/usr/bin/podman stop -t %(stop_grace_period)s %(name)s
 KillMode=none
+Type=forking
+PIDFile=/var/run/%(name)s.pid
 %(sys_exec)s
 [Install]
 WantedBy=multi-user.target""" % s_config)