Add call_retry for ModelBuilder for error recovery

Add call_retry method for ModelBuilder classes along with configuration
options. This allows ModelBuilder classes to reattempt any failed calls
to external services such as Nova or Ironic.

Change-Id: Ided697adebed957e5ff13b4c6b5b06c816f81c4a

releasenotes/notes/api-call-retry-fef741ac684c58dd.yaml

@@ -0,0 +1,9 @@
+---
+features:
+  - |
+    API calls while building the Compute data model will be retried upon
+    failure. The amount of failures allowed before giving up and the time before
+    reattempting are configurable. The `api_call_retries` and
+    `api_query_timeout` parameters in the `[collector]` group can be used to
+    adjust these paremeters. 10 retries with a 1 second time in between
+    reattempts is the default.

watcher/conf/collector.py

@@ -35,6 +35,13 @@ Supported in-tree collectors include:
 Custom data model collector plugins can be defined with the
 ``watcher_cluster_data_model_collectors`` extension point.
 """),
+    cfg.IntOpt('api_call_retries',
+               default=10,
+               help="Number of retries before giving up on external service "
+                    "calls."),
+    cfg.IntOpt('api_query_timeout',
+               default=1,
+               help="Time before retry after failed call to external service.")
 ]
 
 

watcher/decision_engine/model/collector/base.py

@@ -106,6 +106,7 @@ strategies.
 import abc
 import copy
 import threading
+import time
 
 from oslo_config import cfg
 from oslo_log import log
@@ -116,6 +117,7 @@ from watcher.common.loader import loadable
 from watcher.decision_engine.model import model_root
 
 LOG = log.getLogger(__name__)
+CONF = cfg.CONF
 
 
 @six.add_metaclass(abc.ABCMeta)
@@ -194,6 +196,42 @@ class BaseClusterDataModelCollector(loadable.LoadableSingleton):
 
 class BaseModelBuilder(object):
 
+    def call_retry(self, f, *args, **kwargs):
+        """Attempts to call external service
+
+        Attempts to access data from the external service and handles
+        exceptions. The retrieval should be retried in accordance
+        to the value of api_call_retries
+        :param f: The method that performs the actual querying for metrics
+        :param args: Array of arguments supplied to the method
+        :param kwargs: The amount of arguments supplied to the method
+        :return: The value as retrieved from the external service
+        """
+
+        num_retries = CONF.collector.api_call_retries
+        timeout = CONF.collector.api_query_timeout
+
+        for i in range(num_retries):
+            try:
+                return f(*args, **kwargs)
+            except Exception as e:
+                LOG.exception(e)
+                self.call_retry_reset(e)
+                LOG.warning("Retry {0} of {1}, error while calling service "
+                            "retry in {2} seconds".format(i+1, num_retries,
+                                                          timeout))
+                time.sleep(timeout)
+        raise
+
+    @abc.abstractmethod
+    def call_retry_reset(self, exc):
+        """Attempt to recover after encountering an error
+
+        Recover from errors while calling external services, the exception
+        can be used to make a better decision on how to best recover.
+        """
+        pass
+
     @abc.abstractmethod
     def execute(self, model_scope):
         """Build the cluster data model limited to the scope and return it

watcher/decision_engine/model/collector/cinder.py

@@ -176,9 +176,10 @@ class CinderModelBuilder(base.BaseModelBuilder):
         This includes components which represent actual infrastructure
         hardware.
         """
-        for snode in self.cinder_helper.get_storage_node_list():
+        for snode in self.call_retry(
+                self.cinder_helper.get_storage_node_list):
             self.add_storage_node(snode)
-        for pool in self.cinder_helper.get_storage_pool_list():
+        for pool in self.call_retry(self.cinder_helper.get_storage_pool_list):
             pool = self._build_storage_pool(pool)
             self.model.add_pool(pool)
             storage_name = getattr(pool, 'name')
@@ -213,8 +214,8 @@ class CinderModelBuilder(base.BaseModelBuilder):
         except IndexError:
             pass
 
-        volume_type = self.cinder_helper.get_volume_type_by_backendname(
-            backend)
+        volume_type = self.call_retry(
+            self.cinder_helper.get_volume_type_by_backendname, backend)
 
         # build up the storage node.
         node_attributes = {
@@ -262,7 +263,7 @@ class CinderModelBuilder(base.BaseModelBuilder):
         self._add_virtual_storage()
 
     def _add_virtual_storage(self):
-        volumes = self.cinder_helper.get_volume_list()
+        volumes = self.call_retry(self.cinder_helper.get_volume_list)
         for vol in volumes:
             volume = self._build_volume_node(vol)
             self.model.add_volume(volume)

watcher/decision_engine/model/collector/ironic.py

@@ -105,6 +105,6 @@ class BareMetalModelBuilder(base.BaseModelBuilder):
 
     def execute(self, model_scope):
         # TODO(Dantali0n): Use scope to limit size of model
-        for node in self.ironic_helper.get_ironic_node_list():
+        for node in self.call_retry(self.ironic_helper.get_ironic_node_list):
             self.add_ironic_node(node)
         return self.model

watcher/decision_engine/model/collector/nova.py

@@ -211,7 +211,7 @@ class NovaModelBuilder(base.BaseModelBuilder):
         self.nova_helper = nova_helper.NovaHelper(osc=self.osc)
 
     def _collect_aggregates(self, host_aggregates, _nodes):
-        aggregate_list = self.nova_helper.get_aggregate_list()
+        aggregate_list = self.call_retry(f=self.nova_helper.get_aggregate_list)
         aggregate_ids = [aggregate['id'] for aggregate
                          in host_aggregates if 'id' in aggregate]
         aggregate_names = [aggregate['name'] for aggregate
@@ -226,7 +226,7 @@ class NovaModelBuilder(base.BaseModelBuilder):
                 _nodes.update(aggregate.hosts)
 
     def _collect_zones(self, availability_zones, _nodes):
-        service_list = self.nova_helper.get_service_list()
+        service_list = self.call_retry(f=self.nova_helper.get_service_list)
         zone_names = [zone['name'] for zone
                       in availability_zones]
         include_all_nodes = False
@@ -252,14 +252,15 @@ class NovaModelBuilder(base.BaseModelBuilder):
 
         if not compute_nodes:
             self.no_model_scope_flag = True
-            all_nodes = self.nova_helper.get_compute_node_list()
+            all_nodes = self.call_retry(
+                f=self.nova_helper.get_compute_node_list)
             compute_nodes = set(
                 [node.hypervisor_hostname for node in all_nodes])
         LOG.debug("compute nodes: %s", compute_nodes)
         for node_name in compute_nodes:
-            cnode = self.nova_helper.get_compute_node_by_name(node_name,
-                                                              servers=True,
-                                                              detailed=True)
+            cnode = self.call_retry(
+                self.nova_helper.get_compute_node_by_name,
+                node_name, servers=True, detailed=True)
             if cnode:
                 node_info = cnode[0]
                 # filter out baremetal node
@@ -339,9 +340,8 @@ class NovaModelBuilder(base.BaseModelBuilder):
         # compute API. If we need to request more than 1000 servers,
         # we can set limit=-1. For details, please see:
         # https://bugs.launchpad.net/watcher/+bug/1834679
-        instances = self.nova_helper.get_instance_list(
-            filters=filters,
-            limit=limit)
+        instances = self.call_retry(f=self.nova_helper.get_instance_list,
+                                    filters=filters, limit=limit)
         for inst in instances:
             # Add Node
             instance = self._build_instance_node(inst)