Add RemoteRestartContext

Add RemoteRestartContext to process remote restart triggers
down a relation.

charmhelpers/contrib/openstack/context.py

@@ -3445,3 +3445,25 @@ def validate(self):
         dummy_op.update(self.op)
         pool = ch_ceph.BasePool('dummy-service', op=dummy_op)
         pool.validate()
+
+
+class RemoteRestartContext(OSContextGenerator):
+    """Process restart trigger."""
+
+    def __init__(self, relation_name):
+        """
+        :param relation_name: Name of relation to look for restart trigger.
+        :type relation_name: str
+        """
+        self.relation_name = relation_name
+
+    def __call__(self):
+        for rid in relation_ids(self.relation_name):
+            for unit in related_units(rid):
+                restart_uuid = relation_get(
+                    attribute='restart-trigger',
+                    rid=rid,
+                    unit=unit)
+                if restart_uuid:
+                    return {'restart_trigger': restart_uuid}
+        return {}

tests/contrib/openstack/test_os_contexts.py

@@ -4748,6 +4748,13 @@ def test_parse_ovs_use_veth(self, _bool_from_string):
             ctx_object.parse_ovs_use_veth()
             _bool_from_string.assert_called_with("Invalid")
 
+    def test_remote_restarts_context(self):
+        self.relation_ids.return_value = ['rid1']
+        self.related_units.return_value = ['nova-compute/0']
+        self.relation_get.return_value = '123456'
+        ctx_object = context.RemoteRestartContext(relation_name='nova-ceilometer')()
+        self.assertEqual(ctx_object, {'restart_trigger': '123456'})
+
 
 class MockPCIDevice(object):
     """Simple wrapper to mock pci.PCINetDevice class"""