Update

provides.py

@@ -21,7 +21,7 @@ from charms.reactive.bus import get_states
 from charmhelpers.core import hookenv
 
 
-class DNSBackendProvides(RelationBase):
+class BindRNDCProvides(RelationBase):
     scope = scopes.UNIT
 
     @hook('{provides:bind-rndc}-relation-joined')

requires.py

@@ -0,0 +1,52 @@
+#!/usr/bin/python
+# 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 charms.reactive import RelationBase
+from charms.reactive import hook
+from charms.reactive import scopes
+
+
+class BindRNDCRequires(RelationBase):
+    scope = scopes.GLOBAL
+
+    # These remote data fields will be automatically mapped to accessors
+    # with a basic documentation string provided.
+    auto_accessors = ['algorithm', 'secret']
+
+    @hook('{requires:bind-rndc}-relation-joined')
+    def joined(self):
+        self.set_state('{relation_name}.connected')
+
+    @hook('{requires:bind-rndc}-relation-changed')
+    def changed(self):
+        self.set_state('{relation_name}.connected')
+        if self.data_complete():
+            self.set_state('{relation_name}.available')
+
+    @hook('{requires:bind-rndc}-relation-{broken,departed}')
+    def departed_or_broken(self):
+        self.remove_state('{relation_name}.connected')
+        if not self.data_complete():
+            self.remove_state('{relation_name}.available')
+
+    def data_complete(self):
+        """
+        Get the connection string, if available, or None.
+        """
+        data = {
+            'algorithm': self.algorithm(),
+            'secret': self.secret(),
+        }
+        if all(data.values()):
+            return True
+        return False