Remove required healthcheck import of cassandra

The healthcheck code did an import of the cassandra driver even
if the metrics database is configured to be influx. The cassandra
driver is always installed on devstack but may not be in
containers where space is more of a premium.

Change the code to use oslo_utils.importutils to try the import
of the cassandra driver. This allows it to work correctly if no
cassandra driver and metrics database is influx.

Change-Id: I4055230eb7c203eb2ca82777647ab3b0c62bc367

monasca_api/healthcheck/metrics_db_check.py

@@ -1,4 +1,5 @@
 # Copyright 2017 FUJITSU LIMITED
+# (C) Copyright 2017 Hewlett Packard Enterprise Development LP
 #
 # Licensed under the Apache License, Version 2.0 (the "License"); you may
 # not use this file except in compliance with the License. You may obtain
@@ -14,9 +15,9 @@
 
 import requests
 
-from cassandra import cluster
 from oslo_config import cfg
 from oslo_log import log
+from oslo_utils import importutils
 
 from monasca_api.common.repositories import exceptions
 from monasca_api.healthcheck import base
@@ -42,11 +43,19 @@ class MetricsDbCheck(base.BaseHealthCheck):
     Otherwise unhealthy status is returned with explanation.
     """
 
-    def health_check(self):
+    def __init__(self):
+        # Try to import cassandra. Not a problem if it can't be imported as long
+        # as the metrics db is influx
+        self._cluster = importutils.try_import('cassandra.cluster', None)
         metric_driver = CONF.repositories.metrics_driver
-        db = self._detected_database_type(metric_driver)
+        self._db = self._detected_database_type(metric_driver)
+        if self._db == 'cassandra' and self._cluster is None:
+            # Should not happen, but log if it does somehow
+            LOG.error("Metrics Database is Cassandra but cassandra.cluster"
+                      "not importable. Unable to do health check")
 
-        if db == 'influxdb':
+    def health_check(self):
+        if self._db == 'influxdb':
             status = self._check_influxdb_status()
         else:
             status = self._check_cassandra_status()
@@ -63,8 +72,7 @@ class MetricsDbCheck(base.BaseHealthCheck):
             raise exceptions.UnsupportedDriverException(
                 'Driver {0} is not supported by Healthcheck'.format(driver))
 
-    @staticmethod
-    def _check_influxdb_status():
+    def _check_influxdb_status(self):
         uri = 'http://{0}:{1}/ping'.format(CONF.influxdb.ip_address,
                                            CONF.influxdb.port)
         try:
@@ -75,10 +83,11 @@ class MetricsDbCheck(base.BaseHealthCheck):
         return resp.ok, 'OK' if resp.ok else 'Error: {0}'.format(
             resp.status_code)
 
-    @staticmethod
-    def _check_cassandra_status():
+    def _check_cassandra_status(self):
+        if self._cluster is None:
+            return False, "Cassandra driver not imported"
         try:
-            cassandra = cluster.Cluster(
+            cassandra = self._cluster.Cluster(
                 CONF.cassandra.cluster_ip_addresses.split(',')
             )
             session = cassandra.connect(CONF.cassandra.keyspace)

monasca_api/tests/test_metrics_db_health_check.py

@@ -1,4 +1,5 @@
 # Copyright 2017 FUJITSU LIMITED
+# (C) Copyright 2017 Hewlett Packard Enterprise Development LP
 #
 # Licensed under the Apache License, Version 2.0 (the "License"); you may
 # not use this file except in compliance with the License. You may obtain
@@ -147,8 +148,8 @@ class TestMetricsDbHealthCheck(base.BaseTestCase):
         self.assertTrue(result.healthy)
         self.assertEqual('OK', result.message)
 
-    @mock.patch('monasca_api.healthcheck.metrics_db_check.cluster.Cluster')
-    def test_should_fail_cassandra_unavailable(self, cluster):
+    @mock.patch('monasca_api.healthcheck.metrics_db_check.importutils.try_import')
+    def test_should_fail_cassandra_unavailable(self, try_import):
         messaging_conf = {
             'metrics_driver': 'cassandra.metrics_repository:MetricsRepository'
         }
@@ -159,17 +160,40 @@ class TestMetricsDbHealthCheck(base.BaseTestCase):
         self._conf.config(group='repositories', **messaging_conf)
         self._conf.config(group='cassandra', **cassandra_conf)
 
+        cluster = mock.Mock()
         cas_mock = mock.Mock()
-        cluster.side_effect = cl.NoHostAvailable(message='Host unavailable',
-                                                 errors='Unavailable')
-        cluster.return_value = cas_mock
+        cas_mock.side_effect = cl.NoHostAvailable(message='Host unavailable',
+                                                  errors='Unavailable')
+        cluster.Cluster = cas_mock
+        try_import.return_value = cluster
 
         db_health = tdc.MetricsDbCheck()
         result = db_health.health_check()
 
         self.assertFalse(result.healthy)
 
-    @mock.patch('monasca_api.healthcheck.metrics_db_check.cluster.Cluster')
+    @mock.patch('monasca_api.healthcheck.metrics_db_check.importutils.try_import')
+    def test_should_fail_cassandra_no_driver(self, try_import):
+        messaging_conf = {
+            'metrics_driver': 'cassandra.metrics_repository:MetricsRepository'
+        }
+        cassandra_conf = {
+            'cluster_ip_addresses': 'localhost',
+            'keyspace': 'test'
+        }
+        self._conf.config(group='repositories', **messaging_conf)
+        self._conf.config(group='cassandra', **cassandra_conf)
+
+        # Simulate cassandra driver not available
+        try_import.return_value = None
+
+        db_health = tdc.MetricsDbCheck()
+        db_health.cluster = None
+        result = db_health.health_check()
+
+        self.assertFalse(result.healthy)
+
+    @mock.patch('monasca_api.healthcheck.metrics_db_check.importutils.try_import')
     def test_should_pass_cassandra_is_available(self, _):
         messaging_conf = {
             'metrics_driver': 'cassandra.metrics_repository:MetricsRepository'