Add hosted agents list to dhcp agent scheduler

Availability zone aware dhcp scheduler uses hosted agents list
to schedule dhcp agent to proper availability zone.
The scheduler can avoid scheduling the same availalibity zone as
agents host a network which should be distributed for HA.

Change-Id: Ib01f6d852956dc1e89b83321d657c0baf829e28a
Partially-implements: blueprint add-availability-zone

diff --git a/neutron/scheduler/base_scheduler.py b/neutron/scheduler/base_scheduler.py
index 9ed9b806ff1262a94293ab2699c27cd0e36a104c..9a7b1b7d0f1f2730bf19625028cef355c0ca4fa9 100644 (file)
--- a/neutron/scheduler/base_scheduler.py
+++ b/neutron/scheduler/base_scheduler.py
@@ -32,7 +32,7 @@ class BaseScheduler(object):
 
     @abc.abstractmethod
     def select(self, plugin, context, resource_hostable_agents,
-               num_agents_needed):
+               resource_hosted_agents, num_agents_needed):
         """Return a subset of agents based on the specific scheduling logic."""
 
     def schedule(self, plugin, context, resource):
@@ -44,8 +44,9 @@ class BaseScheduler(object):
             plugin, context, resource)
         num_agents = filtered_agents_dict['n_agents']
         hostable_agents = filtered_agents_dict['hostable_agents']
+        hosted_agents = filtered_agents_dict['hosted_agents']
         chosen_agents = self.select(plugin, context, hostable_agents,
-                                    num_agents)
+                                    hosted_agents, num_agents)
         # bind the resource to the agents
         self.resource_filter.bind(context, chosen_agents, resource['id'])
         return chosen_agents
@@ -58,7 +59,7 @@ class BaseChanceScheduler(BaseScheduler):
         self.resource_filter = resource_filter
 
     def select(self, plugin, context, resource_hostable_agents,
-               num_agents_needed):
+               resource_hosted_agents, num_agents_needed):
         chosen_agents = random.sample(resource_hostable_agents,
                                       num_agents_needed)
         return chosen_agents
@@ -71,7 +72,7 @@ class BaseWeightScheduler(BaseScheduler):
         self.resource_filter = resource_filter
 
     def select(self, plugin, context, resource_hostable_agents,
-               num_agents_needed):
+               resource_hosted_agents, num_agents_needed):
         chosen_agents = sorted(resource_hostable_agents,
                            key=attrgetter('load'))[0:num_agents_needed]
         return chosen_agents

diff --git a/neutron/scheduler/dhcp_agent_scheduler.py b/neutron/scheduler/dhcp_agent_scheduler.py
index 6a149440dde41f58f076fa72c30ac761f79b76cc..4dab4f058e7dbe54cec990d1a2db22458c0a3967 100644 (file)
--- a/neutron/scheduler/dhcp_agent_scheduler.py
+++ b/neutron/scheduler/dhcp_agent_scheduler.py
@@ -115,11 +115,20 @@ class DhcpFilter(base_resource_filter.BaseResourceFilter):
         super(DhcpFilter, self).bind(context, bound_agents, network_id)
 
     def filter_agents(self, plugin, context, network):
-        """Return the agents that can host the network."""
+        """Return the agents that can host the network.
+
+        This function returns a dictionary which has 3 keys.
+        n_agents: The number of agents should be scheduled. If n_agents=0,
+        all networks are already scheduled or no more agent can host the
+        network.
+        hostable_agents: A list of agents which can host the network.
+        hosted_agents: A list of agents which already hosts the network.
+        """
         agents_dict = self._get_network_hostable_dhcp_agents(
                                     plugin, context, network)
         if not agents_dict['hostable_agents'] or agents_dict['n_agents'] <= 0:
-            return {'n_agents': 0, 'hostable_agents': []}
+            return {'n_agents': 0, 'hostable_agents': [],
+                    'hosted_agents': agents_dict['hosted_agents']}
         return agents_dict
 
     def _get_dhcp_agents_hosting_network(self, plugin, context, network):
@@ -151,17 +160,21 @@ class DhcpFilter(base_resource_filter.BaseResourceFilter):
         return active_dhcp_agents
 
     def _get_network_hostable_dhcp_agents(self, plugin, context, network):
-        """Return number of agents which will actually host the given network
-           and a list of dhcp agents which can host the given network
+        """Provide information on hostable DHCP agents for network.
+
+        The returned value includes the number of agents that will actually
+        host the given network, a list of DHCP agents that can host the given
+        network, and a list of DHCP agents currently hosting the network.
         """
         hosted_agents = self._get_dhcp_agents_hosting_network(plugin,
                                                               context, network)
         if hosted_agents is None:
-            return {'n_agents': 0, 'hostable_agents': []}
+            return {'n_agents': 0, 'hostable_agents': [], 'hosted_agents': []}
         n_agents = cfg.CONF.dhcp_agents_per_network - len(hosted_agents)
         active_dhcp_agents = self._get_active_agents(plugin, context)
         if not active_dhcp_agents:
-            return {'n_agents': 0, 'hostable_agents': []}
+            return {'n_agents': 0, 'hostable_agents': [],
+                    'hosted_agents': hosted_agents}
         hostable_dhcp_agents = [
             agent for agent in set(active_dhcp_agents)
             if agent not in hosted_agents and plugin.is_eligible_agent(
@@ -169,7 +182,8 @@ class DhcpFilter(base_resource_filter.BaseResourceFilter):
         ]
 
         if not hostable_dhcp_agents:
-            return {'n_agents': 0, 'hostable_agents': []}
+            return {'n_agents': 0, 'hostable_agents': [],
+                    'hosted_agents': hosted_agents}
         n_agents = min(len(hostable_dhcp_agents), n_agents)
-        return {'n_agents': n_agents, 'hostable_agents':
-                hostable_dhcp_agents}
+        return {'n_agents': n_agents, 'hostable_agents': hostable_dhcp_agents,
+                'hosted_agents': hosted_agents}