Config option for model handlers and backends

The model handlers and their corresponding backends can now be
specified in the configuration file of the shim layer. For every
model handler, one particular backend can be specified in a
dict.

Change-Id: I5866e921850b9bfc16f5815744f692bfe432b330
Signed-off-by: Georg Kunz <georg.kunz@ericsson.com>

etc/shim/proton-shim.conf.sample

@@ -11,6 +11,11 @@ etcd_port = 2379
 # host_list = host1,host2,host3
 host_list = *
 
+# Select the model to load with the corresponding backend. This config option is a dict
+# where the key represents the name of the model and the value the name of the backend
+# which is to be used for this model.
+handlers = net-l3vpn:net-l3vpn-odl
+
 
 [shim_odl]
 # IP of the OpenDaylight RESTconf interface. Typically needs to be changed after installation.

gluon/shim/api_models/net_l3vpn.py

@@ -27,8 +27,8 @@ LOG = logging.getLogger(__name__)
 
 class ApiNetL3VPN(ApiModelBase):
 
-    def __init__(self, backend):
-        super(self.__class__, self).__init__("net-l3vpn", backend)
+    def __init__(self):
+        super(self.__class__, self).__init__("net-l3vpn")
         self.resync_mode = False
         self.model.vpn_instances = dict()
         self.model.vpn_ports = dict()

gluon/shim/base.py

@@ -22,7 +22,7 @@ from gluon.shim.model import Model
 
 class ApiModelBase(object):
 
-    def __init__(self, _name, _backend):
+    def __init__(self, _name):
         """Init Method.
 
         :param _name: name of the API Servce (e.g. net-l3vpn)
@@ -30,9 +30,11 @@ class ApiModelBase(object):
         :returns: None
         """
         self.model = Model()      # Internal Model for the API Service
-        self.backend = _backend   # ControllerModelBase
         self.name = _name
 
+    def init(self, backend):
+        self.backend = backend    # ControllerModelBase
+
     def handle_object_change(self, object, key, attributes, shim_data):
         """Called to update model based on changes to etcd database.
 

gluon/shim/main.py

@@ -13,6 +13,7 @@
 #    License for the specific language governing permissions and limitations
 #    under the License.
 
+import etcd
 import json
 import os
 import sys
@@ -21,13 +22,11 @@ import time
 from Queue import Queue
 from threading import Thread
 
-import etcd
-
 from oslo_config import cfg
 from oslo_log import log as logging
 
-from gluon.shim.api_models.net_l3vpn import ApiNetL3VPN
-from gluon.shim.backends.opendaylight.odl_net_l3vpn import OdlNetL3VPN
+from stevedore import extension
+
 from gluon.shim.utils import pretty_print_message
 
 
@@ -96,14 +95,40 @@ def process_message(message):
 
 
 def setup_app():
-    #
-    # This should be config file driven to define the
-    # APIs that are handled and the backend to handle each API
-    #
-    backend = OdlNetL3VPN()
-    handler = ApiNetL3VPN(backend)
-    ShimData.api_handlers[handler.name] = handler
-    handler.load_model(ShimData)
+    api_models = extension.ExtensionManager(
+        namespace='gluon.shim.models',
+        invoke_on_load=True
+    )
+
+    backends = extension.ExtensionManager(
+        namespace='gluon.shim.backends',
+        invoke_on_load=True
+    )
+
+    def init_model(model, backends):
+        if model.obj.name in CONF.shim.handlers:
+            backend_name = CONF.shim.handlers[model.obj.name]
+            if backend_name in backends:
+                backend = backends[backend_name]
+                model.obj.init(backend.obj)
+                LOG.info('Loaded handler "%s" with backend "%s"' %
+                         (model.obj.name, backend_name))
+                return model.obj
+            else:
+                LOG.error('Cannot load backend for handler "%s": '
+                          'Selected backend "%s" not found.' %
+                          (model.obj.name, backend_name))
+        else:
+            LOG.info('Handler "%s" not selected in config file. '
+                     'Skipping initialization.' %
+                     model.obj.name)
+
+    handlers = api_models.map(init_model, backends)
+
+    for handler in handlers:
+        if handler is not None:
+            ShimData.api_handlers[handler.name] = handler
+            handler.load_model(ShimData)
 
 
 def prepare_service(argv=()):
@@ -123,6 +148,10 @@ def main():
                    default='*',
                    help='Comma separated list of hostnames managed by '
                         'this server'),
+        cfg.DictOpt('handlers',
+                    default={'net-l3vpn': 'net-l3vpn-odl'},
+                    help='Dict for selecting the handlers '
+                         'and their corresponding backend.')
     ]
     opt_group = cfg.OptGroup(name='shim',
                              title='Options for the sample shim service')

setup.cfg

@@ -39,6 +39,13 @@ gluon.backends =
 gluon.managers =
     net-l3vpn = gluon.managers.models.net_l3vpn:Provider
 
+gluon.shim.models =
+    net-l3vpn = gluon.shim.api_models.net_l3vpn:ApiNetL3VPN
+
+gluon.shim.backends =
+    net-l3vpn-odl = gluon.shim.backends.opendaylight.odl_net_l3vpn:OdlNetL3VPN
+    net-l3vpn-dummy = gluon.shim.backends.dummy_net_l3vpn:DummyNetL3VPN
+
 neutron.core_plugins =
     gluon = gluon.plugin.core:GluonPlugin