add sdnotify support to cli, for Systemd

fixes #1318 systemd recommends against Type=forking, preferring
TYPE=notify. To do that, we need to make little api calls
during startup and shutdown. Added those.

This makes systemd happier on startup and seems to show status
messages correctly.

Author: petersilva

debian/metpx-sr3.service

@@ -11,7 +11,7 @@ After=network-online.target local-fs.target remote-fs.target
 Requires=network-online.target
 
 [Service]
-Type=forking
+Type=Notify
 ExecStart=/usr/bin/sr3 start
 User=sarra
 Group=sarra

sarracenia/featuredetection.py

@@ -91,6 +91,10 @@
     's3' : { 'modules_needed': [ 'boto3' ], 'present': False, 
         'lament' : 'cannot connect natively to S3-compatible locations (AWS S3, Minio, etc..)', 
         'rejoice': 'able to connect natively to S3-compatible locations (AWS S3, Minio, etc..)', },
+   'sdnotify' : { 'modules_needed': [ 'sdnotify' ],
+        'lament': 'cannot inform system of correct startup.',
+        'rejoice': 'can tell system when correctly started.'
+        },
    'sftp' : { 'modules_needed': [ 'paramiko' ],
         'lament': 'cannot use or access sftp/ssh based services',
         'rejoice': 'can use sftp or ssh based services'

sarracenia/sr.py

@@ -2276,6 +2276,13 @@ def start(self):
 
         print('( %d ) Done' % pcount)
 
+        if sarracenia.features['sdnotify']['present']:
+            import sdnotify
+
+            n = sdnotify.SystemdNotifier()
+            n.notify("READY=1")
+
+
     def run(self):
         """
             docker compatible run in foreground.
@@ -2307,6 +2314,12 @@ def stop(self):
 
         self._clean_missing_proc_state()
 
+        if sarracenia.features['sdnotify']['present']:
+            import sdnotify
+
+            n = sdnotify.SystemdNotifier()
+            n.notify("STOPPING=1")
+
         if len(self.procs) == 0:
             print('no procs running...already stopped')
             return