[Sys Mon] Fix the service entry delete in state_db because of timer job (#14702)

Why I did it
systemd stop event on service with timers can sometime delete the state_db entry for the corresponding service.

Note: This won't be observed on the latest master label since the dependency on timer was removed with the recent config reload enhancement. However, it is better to have the fix since there might be some systemd services added to system health daemon in the future which may contain timers

root@qa-eth-vt01-4-3700c:/home/admin# systemctl stop snmp
root@qa-eth-vt01-4-3700c:/home/admin# show system-health sysready-status 
System is not ready - one or more services are not up

Service-Name            Service-Status    App-Ready-Status    Down-Reason
----------------------  ----------------  ------------------  -------------
<Truncated>
ssh                     OK                OK                  -
swss                    OK                OK                  -
syncd                   OK                OK                  -
sysstat                 OK                OK                  -
teamd                   OK                OK                  -
telemetry               OK                OK                  -
what-just-happened      OK                OK                  -
ztp                     OK                OK                  -
<Truncated>
Expected

Should see a Down entry for SNMP instead of the entry being deleted from the STATE_DB

root@qa-eth-vt01-4-3700c:/home/admin# show system-health sysready-status 
System is not ready - one or more services are not up

Service-Name            Service-Status    App-Ready-Status    Down-Reason
----------------------  ----------------  ------------------  -------------
<Truncated>
snmp                    Down              Down                Inactive
ssh                     OK                OK                  -
swss                    OK                OK                  -
syncd                   OK                OK                  -
sysstat                 OK                OK                  -
teamd                   OK                OK                  -
telemetry               OK                OK                  -
what-just-happened      OK                OK                  -
ztp                     OK                OK                  -
<Truncated>
How I did it
Happens because the timer is usually a PartOf service and thus a stop on service is propagated to timer. Fixed the logic to handle this

Apr 18 02:06:47.711252 r-lionfish-16 DEBUG healthd: Main process- received event:snmp.service from source:sysbus time:2023-04-17 23:06:47
Apr 18 02:06:47.711347 r-lionfish-16 INFO healthd: check_unit_status for [ snmp.service ] 
Apr 18 02:06:47.722363 r-lionfish-16 INFO healthd: snmp.service service state changed to [inactive/dead]

Apr 18 02:06:47.723230 r-lionfish-16 DEBUG healthd: Main process- received event:snmp.timer from source:sysbus time:2023-04-17 23:06:47
Apr 18 02:06:47.723328 r-lionfish-16 INFO healthd: check_unit_status for [ snmp.timer ] 

Signed-off-by: Vivek Reddy Karri <[email protected]>

Author: vivekrnv

src/system-health/health_checker/sysmonitor.py

@@ -407,10 +407,13 @@ def check_unit_status(self, event):
                 self.dnsrvs_name.remove(event)
 
             srv_name,last = event.split('.')
-            key = 'ALL_SERVICE_STATUS|{}'.format(srv_name)
-            key_exists = self.state_db.exists(self.state_db.STATE_DB, key)
-            if key_exists == 1:
-                self.state_db.delete(self.state_db.STATE_DB, key)
+            # stop on service maybe propagated to timers and in that case,
+            # the state_db entry for the service should not be deleted
+            if last == "service":
+                key = 'ALL_SERVICE_STATUS|{}'.format(srv_name)
+                key_exists = self.state_db.exists(self.state_db.STATE_DB, key)
+                if key_exists == 1:
+                    self.state_db.delete(self.state_db.STATE_DB, key)
 
         return 0
 

src/system-health/tests/test_system_health.py

@@ -654,6 +654,15 @@ def test_check_unit_status():
     assert 'mock_bgp.service' in sysmon.dnsrvs_name
 
 
+@patch('health_checker.sysmonitor.Sysmonitor.get_all_service_list', MagicMock(return_value=['mock_snmp.service']))
+def test_check_unit_status_timer():
+    sysmon = Sysmonitor()
+    sysmon.state_db = MagicMock()
+    sysmon.state_db.exists = MagicMock(return_value=1)
+    sysmon.state_db.delete = MagicMock()
+    sysmon.check_unit_status('mock_snmp.timer')
+    assert not sysmon.state_db.delete.called
+
 
 @patch('health_checker.sysmonitor.Sysmonitor.run_systemctl_show', MagicMock(return_value=mock_srv_props['mock_radv.service']))
 @patch('health_checker.sysmonitor.Sysmonitor.get_app_ready_status', MagicMock(return_value=('Up','-','-')))