Add new config option use_aggregated_uve_db

Provide an option to enable/disable serve UVE queries from the aggregated
UVE db. In a scale setup, HA event (alarm-gen down), alarm-gen may take a
long time to aggregate the UVEs depending on the number of UVEs, number
of partitions it owns, etc., So, enabling this option would reduce the
down time in case of HA events (collector down - time taken for generators
 to connect to the new collector and resync the UVEs, alarm-gen down - no
impact on UVE queries, only the alarms would be reevaluated)

Change-Id: If39df7650ec514d4645e3eae30edc7b8ed0b5d1d
Closes-Bug: #1719236

src/opserver/opserver.py

@@ -445,6 +445,7 @@ def _reject_auth_headers(self):
     def __init__(self, args_str=' '.join(sys.argv[1:])):
         self.gevs = []
         self._args = None
+        self._usecache = True
         self._parse_args(args_str)
         print args_str
 
@@ -534,7 +535,6 @@ def __init__(self, args_str=' '.join(sys.argv[1:])):
 
         # On olders version of linux, kafka cannot be
         # relied upon. DO NOT use it to serve UVEs
-        self._usecache = True
         (PLATFORM, VERSION, EXTRA) = platform.linux_distribution()
         if PLATFORM.lower() == 'ubuntu':
             if VERSION.find('12.') == 0:
@@ -849,6 +849,7 @@ def _parse_args(self, args_str=' '.join(sys.argv[1:])):
             'admin_port'        : OpServerAdminPort,
             'cloud_admin_role'  : CLOUD_ADMIN_ROLE,
             'api_server_use_ssl': False,
+            'use_aggregated_uve_db' : 'true',
         }
         redis_opts = {
             'redis_server_port'  : 6379,
@@ -1009,6 +1010,8 @@ def _parse_args(self, args_str=' '.join(sys.argv[1:])):
             help="Port with local auth for admin access")
         parser.add_argument("--api_server_use_ssl",
             help="Use SSL to connect with API server")
+        parser.add_argument("--use_aggregated_uve_db",
+            help="enable/disbale read uve from aggregated uve db")
         self._args = parser.parse_args(remaining_argv)
         if type(self._args.collectors) is str:
             self._args.collectors = self._args.collectors.split()
@@ -1035,6 +1038,9 @@ def _parse_args(self, args_str=' '.join(sys.argv[1:])):
         auth_conf_info['api_server_ip'] = api_server_info[0]
         auth_conf_info['api_server_port'] = int(api_server_info[1])
         self._args.auth_conf_info = auth_conf_info
+        if self._args.use_aggregated_uve_db.lower() == 'false' or\
+           self._args.use_aggregated_uve_db == '0':
+            self._usecache = False
     # end _parse_args
 
     def get_args(self):
@@ -2462,10 +2468,11 @@ def get_agp(self):
         return self.agp
 
     def run(self):
-        self._uvedbstream.start()
+        if self._usecache:
+            self._uvedbstream.start()
+            self.gevs.append(self._uvedbstream)
 
         self.gevs += [
-            self._uvedbstream,
             gevent.spawn(self.start_webserver),
             gevent.spawn(self.start_uve_server),
             ]