Add a new lbaas agent Scheduler, LeastPoolAgentScheduler

LeastPoolAgentScheduler assigns a pool to an lbaas-agent
with the least number of pools. When there are multiple
lbaas-agents on multiple nodes, pools will be evenly
distributed over the agents. Thus this scheduler helps
the scalability of lbaas-agents serving large number of pools.
At the moment only available lbaas-agent scheduler is ChanceScheduler.

Co-Authored-By: Adam Harwell <flux.adam@gmail.com>
Change-Id: I0b920a8bb5b2918dd5f47ef2a81d3009896af47d

etc/neutron_lbaas.conf

@@ -1,6 +1,7 @@
 [DEFAULT]
 # =========== items for agent scheduler extension =============
 # loadbalancer_pool_scheduler_driver = neutron.services.loadbalancer.agent_scheduler.ChanceScheduler
+# loadbalancer_pool_scheduler_driver = neutron.services.loadbalancer.agent_scheduler.LeastPoolAgentScheduler
 # loadbalancer_scheduler_driver = neutron.agent_scheduler.ChanceScheduler
 
 [quotas]

neutron_lbaas/services/loadbalancer/agent_scheduler.py

@@ -14,6 +14,7 @@
 #    under the License.
 
 import random
+import sys
 
 from neutron.common import constants
 from neutron.db import agents_db
@@ -26,6 +27,7 @@ import sqlalchemy as sa
 from sqlalchemy import orm
 from sqlalchemy.orm import joinedload
 
+from abc import abstractmethod
 from neutron_lbaas.extensions import lbaas_agentscheduler
 
 LOG = logging.getLogger(__name__)
@@ -80,6 +82,11 @@ class LbaasAgentSchedulerDbMixin(agentschedulers_db.AgentSchedulerDbMixin,
         else:
             return {'pools': []}
 
+    def num_of_pools_on_lbaas_agent(self, context, id):
+        query = context.session.query(PoolLoadbalancerAgentBinding.pool_id)
+        query = query.filter_by(agent_id=id)
+        return query.count()
+
     def get_lbaas_agent_candidates(self, device_driver, active_agents):
         candidates = []
         for agent in active_agents:
@@ -89,8 +96,7 @@ class LbaasAgentSchedulerDbMixin(agentschedulers_db.AgentSchedulerDbMixin,
         return candidates
 
 
-class ChanceScheduler(object):
-    """Allocate a loadbalancer agent for a vip in a random way."""
+class SchedulerBase(object):
 
     def schedule(self, plugin, context, pool, device_driver):
         """Schedule the pool to an active loadbalancer agent if there
@@ -118,7 +124,8 @@ class ChanceScheduler(object):
                          device_driver)
                 return
 
-            chosen_agent = random.choice(candidates)
+            chosen_agent = self._schedule(candidates, plugin, context)
+
             binding = PoolLoadbalancerAgentBinding()
             binding.agent = chosen_agent
             binding.pool_id = pool['id']
@@ -128,3 +135,29 @@ class ChanceScheduler(object):
                       {'pool_id': pool['id'],
                        'agent_id': chosen_agent['id']})
             return chosen_agent
+
+    @abstractmethod
+    def _schedule(self, candidates, plugin, context):
+        pass
+
+
+class ChanceScheduler(SchedulerBase):
+
+    def _schedule(self, candidates, plugin, context):
+        """Allocate a loadbalancer agent for a vip in a random way."""
+        return random.choice(candidates)
+
+
+class LeastPoolAgentScheduler(SchedulerBase):
+
+    def _schedule(self, candidates, plugin, context):
+        """Pick an agent with least number of pools from candidates"""
+        current_min_pool_num = sys.maxint
+        # SchedulerBase.schedule() already checks for empty candidates
+        for tmp_agent in candidates:
+            tmp_pool_num = plugin.num_of_pools_on_lbaas_agent(
+                context, tmp_agent['id'])
+            if current_min_pool_num > tmp_pool_num:
+                current_min_pool_num = tmp_pool_num
+                chosen_agent = tmp_agent
+        return chosen_agent

neutron_lbaas/tests/unit/services/loadbalancer/test_agent_scheduler.py

@@ -73,7 +73,7 @@ class LBaaSAgentSchedulerTestCase(test_agent.AgentDBTestMixIn,
         service_plugins = {
             'lb_plugin_name': test_db_loadbalancer.DB_LB_PLUGIN_KLASS}
 
-        #default provider should support agent scheduling
+        # default provider should support agent scheduling
         cfg.CONF.set_override(
             'service_provider',
             [('LOADBALANCER:lbaas:neutron_lbaas.services.'
@@ -217,3 +217,15 @@ class LBaaSAgentSchedulerTestCase(test_agent.AgentDBTestMixIn,
                 'fake_id',
                 expected_code=exc.HTTPForbidden.code,
                 admin_context=False)
+
+
+class LeastPoolAgentSchedulerTestCase(LBaaSAgentSchedulerTestCase):
+
+    def setUp(self):
+        # Setting LeastPoolAgentScheduler as scheduler
+        cfg.CONF.set_override(
+            'loadbalancer_pool_scheduler_driver',
+            'neutron_lbaas.services.loadbalancer.'
+            'agent_scheduler.LeastPoolAgentScheduler')
+
+        super(LeastPoolAgentSchedulerTestCase, self).setUp()

setup.cfg

@@ -48,6 +48,7 @@ loadbalancer_schedulers =
     neutron_lbaas.agent_scheduler.ChanceScheduler = neutron_lbaas.agent_scheduler:ChanceScheduler
 pool_schedulers =
     neutron.services.loadbalancer.agent_scheduler.ChanceScheduler = neutron_lbaas.services.loadbalancer.agent_scheduler:ChanceScheduler
+    neutron.services.loadbalancer.agent_scheduler.LeastPoolAgentScheduler = neutron_lbaas.services.loadbalancer.agent_scheduler:LeastPoolAgentScheduler
 
 [build_sphinx]
 all_files = 1