add retry-attempt logic if no metaData returned by the pmcollector

there are some situation where no data returned from the pmcollector
because the REST HTTPS server did not complete starting yet and no data
request was sent to the pmcollector. For such situation the bridge
should retry to get metadata wihout stopping.

MAX_ATTEMPTS_COUNT = 3
SLEEP_TIME = 5sec

Author: Helene

source/messages.py

@@ -42,6 +42,7 @@
        'InconsistentParams': 'Received parameters {} inconsistent with request parameters {}',
        'SensorDisabled': 'Sensor for metric {} is disabled',
        'NoData': 'Empty results received',  # Please check the pmcollector is properly configured and running.
+       'NoDataStartNextAttempt': 'No Metadata results received from the pmcollector. Start retry attempt {} in 5s (MAX_ATTEMPTS_COUNT:{})',
        'BucketsizeChange': 'Based on requested downsample value: {} the bucketsize will be set: {}',
        'BucketsizeToPeriod': 'Bucketsize will be set to sensors period: {}',
        'ReceivedQuery': 'Received query request for query:{}, start:{}, end:{}',

source/zimonGrafanaIntf.py

@@ -38,6 +38,7 @@
 from confParser import getSettings
 from collections import defaultdict
 from timeit import default_timer as timer
+from time import sleep
 
 
 class MetadataHandler():
@@ -78,18 +79,27 @@ def __initializeTables(self):
 
         self.__qh = QueryHandler(self.server, self.port, self.logger, self.apiKeyName, self.apiKeyValue)
         self.__sensorsConf = SensorConfig.readSensorsConfigFromMMSDRFS(self.logger)
-        tstart = timer()
-        self.__metaData = Topo(self.qh.getTopology())
-        tend = timer()
-        if not (self.metaData and self.metaData.topo):
-            raise ValueError(MSG['NoData'])
-        foundItems = len(self.metaData.allParents) - 1
-        sensors = self.metaData.sensorsSpec.keys()
-        self.logger.info(MSG['MetaSuccess'])
-        self.logger.details(MSG['ReceivAttrValues'].format('parents totally', foundItems))
-        self.logger.debug(MSG['ReceivAttrValues'].format('parents', ", ".join(self.metaData.allParents)))
-        self.logger.info(MSG['ReceivAttrValues'].format('sensors', ", ".join(sensors)))
-        self.logger.details(MSG['TimerInfo'].format('Metadata', str(tend - tstart)))
+        MAX_ATTEMPTS_COUNT = 3
+        for attempt in range(1, MAX_ATTEMPTS_COUNT + 1):
+            tstart = timer()
+            self.__metaData = Topo(self.qh.getTopology())
+            tend = timer()
+            if not (self.metaData and self.metaData.topo):
+                if attempt > MAX_ATTEMPTS_COUNT:
+                    break
+                # if no data returned because of the REST HTTP server is still starting, sleep and retry (max 3 times)
+                self.logger.warning(MSG['NoDataStartNextAttempt'].format(attempt, MAX_ATTEMPTS_COUNT))
+                sleep(5) 
+            else:
+                foundItems = len(self.metaData.allParents) - 1
+                sensors = self.metaData.sensorsSpec.keys()
+                self.logger.info(MSG['MetaSuccess'])
+                self.logger.details(MSG['ReceivAttrValues'].format('parents totally', foundItems))
+                self.logger.debug(MSG['ReceivAttrValues'].format('parents', ", ".join(self.metaData.allParents)))
+                self.logger.info(MSG['ReceivAttrValues'].format('sensors', ", ".join(sensors)))
+                self.logger.details(MSG['TimerInfo'].format('Metadata', str(tend - tstart)))
+                return
+        raise ValueError(MSG['NoData'])
 
     def update(self):
         '''Read the topology from ZIMon and update