Create OpenStackClients convenience class

The OpenStackClients class provides a convenient way to create and
cache client instances.  The idea behind this code comes from Magnum
[0].

The OpenStackClients class will act as the manager of other project's
clients, providing an easy way to fetch instances of said clients. This
will allow the clients to be cached.

An instance of OpenStackClients is created for every call that comes
into the decision engine and the applier, using the request context to
pass needed (domain id) parameters to get a Keystone session.  This
instance should be shared as much as possible to avoid additional
unneccessary connections to the other services.

This class will also allow for the version of each client to be
configurable via the watcher.conf file.

The method by which a Keystone session is also changed to use the
keystoneauth1.loading library.  In order to avoid DuplicateOptErrors
with the keystone_authtoken group used for the keystonemiddleware in the
API code, a new conf group named "watcher_clients_auth" is created.  A
typical configuration using a password authentication scheme will look
like:
  [watcher_clients_auth]
  auth_type = password
  auth_url = http://<server-ip>:<port>
  username = <username>
  password = <password>
  project_domain_id = default
  user_domain_id = default

[0]: https://github.com/openstack/magnum/blob/master/magnum/common/clients.py

DocImpact
Change-Id: Iab9d0b304099686da2e9e2b19e8b1de4332ff378
Implements: blueprint external-api-versioning
Closes-Bug: #1530790
Closes-Bug: #1539670
Closes-Bug: #1522774

watcher/common/clients.py

@@ -0,0 +1,158 @@
+# Licensed under the Apache License, Version 2.0 (the "License"); you may
+# not use this file except in compliance with the License. You may obtain
+# a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+# License for the specific language governing permissions and limitations
+# under the License.
+
+from ceilometerclient import client as ceclient
+from cinderclient import client as ciclient
+from glanceclient import client as glclient
+from keystoneauth1 import loading as ka_loading
+from keystoneclient import client as keyclient
+from neutronclient.neutron import client as netclient
+from novaclient import client as nvclient
+from oslo_config import cfg
+
+from watcher._i18n import _
+from watcher.common import exception
+
+
+NOVA_CLIENT_OPTS = [
+    cfg.StrOpt('api_version',
+               default='2',
+               help=_('Version of Nova API to use in novaclient.'))]
+
+GLANCE_CLIENT_OPTS = [
+    cfg.StrOpt('api_version',
+               default='2',
+               help=_('Version of Glance API to use in glanceclient.'))]
+
+CINDER_CLIENT_OPTS = [
+    cfg.StrOpt('api_version',
+               default='2',
+               help=_('Version of Cinder API to use in cinderclient.'))]
+
+CEILOMETER_CLIENT_OPTS = [
+    cfg.StrOpt('api_version',
+               default='2',
+               help=_('Version of Ceilometer API to use in '
+                      'ceilometerclient.'))]
+
+NEUTRON_CLIENT_OPTS = [
+    cfg.StrOpt('api_version',
+               default='2',
+               help=_('Version of Neutron API to use in neutronclient.'))]
+
+cfg.CONF.register_opts(NOVA_CLIENT_OPTS, group='nova_client')
+cfg.CONF.register_opts(GLANCE_CLIENT_OPTS, group='glance_client')
+cfg.CONF.register_opts(CINDER_CLIENT_OPTS, group='cinder_client')
+cfg.CONF.register_opts(CEILOMETER_CLIENT_OPTS, group='ceilometer_client')
+cfg.CONF.register_opts(NEUTRON_CLIENT_OPTS, group='neutron_client')
+
+_CLIENTS_AUTH_GROUP = 'watcher_clients_auth'
+
+ka_loading.register_auth_conf_options(cfg.CONF, _CLIENTS_AUTH_GROUP)
+ka_loading.register_session_conf_options(cfg.CONF, _CLIENTS_AUTH_GROUP)
+
+
+class OpenStackClients(object):
+    """Convenience class to create and cache client instances."""
+
+    def __init__(self):
+        self.reset_clients()
+
+    def reset_clients(self):
+        self._session = None
+        self._keystone = None
+        self._nova = None
+        self._glance = None
+        self._cinder = None
+        self._ceilometer = None
+        self._neutron = None
+
+    def _get_keystone_session(self):
+        auth = ka_loading.load_auth_from_conf_options(cfg.CONF,
+                                                      _CLIENTS_AUTH_GROUP)
+        sess = ka_loading.load_session_from_conf_options(cfg.CONF,
+                                                         _CLIENTS_AUTH_GROUP,
+                                                         auth=auth)
+        return sess
+
+    @property
+    def auth_url(self):
+        return self.keystone().auth_url
+
+    @property
+    def session(self):
+        if not self._session:
+            self._session = self._get_keystone_session()
+        return self._session
+
+    def _get_client_option(self, client, option):
+        return getattr(getattr(cfg.CONF, '%s_client' % client), option)
+
+    @exception.wrap_keystone_exception
+    def keystone(self):
+        if not self._keystone:
+            self._keystone = keyclient.Client(session=self.session)
+
+        return self._keystone
+
+    @exception.wrap_keystone_exception
+    def nova(self):
+        if self._nova:
+            return self._nova
+
+        novaclient_version = self._get_client_option('nova', 'api_version')
+        self._nova = nvclient.Client(novaclient_version,
+                                     session=self.session)
+        return self._nova
+
+    @exception.wrap_keystone_exception
+    def glance(self):
+        if self._glance:
+            return self._glance
+
+        glanceclient_version = self._get_client_option('glance', 'api_version')
+        self._glance = glclient.Client(glanceclient_version,
+                                       session=self.session)
+        return self._glance
+
+    @exception.wrap_keystone_exception
+    def cinder(self):
+        if self._cinder:
+            return self._cinder
+
+        cinderclient_version = self._get_client_option('cinder', 'api_version')
+        self._cinder = ciclient.Client(cinderclient_version,
+                                       session=self.session)
+        return self._cinder
+
+    @exception.wrap_keystone_exception
+    def ceilometer(self):
+        if self._ceilometer:
+            return self._ceilometer
+
+        ceilometerclient_version = self._get_client_option('ceilometer',
+                                                           'api_version')
+        self._ceilometer = ceclient.Client(ceilometerclient_version,
+                                           session=self.session)
+        return self._ceilometer
+
+    @exception.wrap_keystone_exception
+    def neutron(self):
+        if self._neutron:
+            return self._neutron
+
+        neutronclient_version = self._get_client_option('neutron',
+                                                        'api_version')
+        self._neutron = netclient.Client(neutronclient_version,
+                                         session=self.session)
+        self._neutron.format = 'json'
+        return self._neutron