Remove and block DB access in dhcpbridge

This fixes an issue of direct DB access from happening in dhcpbridge
by using an object method instead. For this to work and to prohibit
future DB access from happening, the objects indirection API is set
and DB access is blocked in a similar way to how it is done in
nova-compute and nova-network.

Change-Id: I5e3152aad13343a6a1ecd9b5b511429159c9d4c2
Closes-Bug: #1316074

nova/cmd/dhcpbridge.py

@@ -22,13 +22,18 @@ from __future__ import print_function
 
 import os
 import sys
+import traceback
 
 from oslo.config import cfg
 
+from nova.conductor import rpcapi as conductor_rpcapi
 from nova import config
 from nova import context
-from nova import db
+import nova.db.api
+from nova import exception
 from nova.network import rpcapi as network_rpcapi
+from nova.objects import base as objects_base
+from nova.objects import network as network_obj
 from nova.openstack.common.gettextutils import _
 from nova.openstack.common import importutils
 from nova.openstack.common import jsonutils
@@ -38,6 +43,7 @@ from nova import rpc
 CONF = cfg.CONF
 CONF.import_opt('host', 'nova.netconf')
 CONF.import_opt('network_manager', 'nova.service')
+CONF.import_opt('use_local', 'nova.conductor.api', group='conductor')
 LOG = logging.getLogger(__name__)
 
 
@@ -65,9 +71,9 @@ def del_lease(mac, ip_address):
 def init_leases(network_id):
     """Get the list of hosts for a network."""
     ctxt = context.get_admin_context()
-    network_ref = db.network_get(ctxt, network_id)
+    network = network_obj.Network.get_by_id(ctxt, network_id)
     network_manager = importutils.import_object(CONF.network_manager)
-    return network_manager.get_dhcp_leases(ctxt, network_ref)
+    return network_manager.get_dhcp_leases(ctxt, network)
 
 
 def add_action_parsers(subparsers):
@@ -92,6 +98,20 @@ CONF.register_cli_opt(
                       handler=add_action_parsers))
 
 
+def block_db_access():
+    class NoDB(object):
+        def __getattr__(self, attr):
+            return self
+
+        def __call__(self, *args, **kwargs):
+            stacktrace = "".join(traceback.format_stack())
+            LOG.error(_('No db access allowed in nova-dhcpbridge: %s'),
+                      stacktrace)
+            raise exception.DBNotAllowed('nova-dhcpbridge')
+
+    nova.db.api.IMPL = NoDB()
+
+
 def main():
     """Parse environment and arguments and call the appropriate action."""
     config.parse_args(sys.argv,
@@ -101,6 +121,11 @@ def main():
     global LOG
     LOG = logging.getLogger('nova.dhcpbridge')
 
+    if not CONF.conductor.use_local:
+        block_db_access()
+        objects_base.NovaObject.indirection_api = \
+            conductor_rpcapi.ConductorAPI()
+
     if CONF.action.name in ['add', 'del', 'old']:
         msg = (_("Called '%(action)s' for mac '%(mac)s' with ip '%(ip)s'") %
                {"action": CONF.action.name,