diff --git a/hooks/charmhelpers/contrib/openstack/cert_utils.py b/hooks/charmhelpers/contrib/openstack/cert_utils.py
index a25ca995..6620f59f 100644
--- a/hooks/charmhelpers/contrib/openstack/cert_utils.py
+++ b/hooks/charmhelpers/contrib/openstack/cert_utils.py
@@ -414,18 +414,27 @@ def get_requests_for_local_unit(relation_name=None):
         is_legacy_request = set(sent).intersection(legacy_keys)
         for unit in related_units(rid):
             data = relation_get(rid=rid, unit=unit)
-            if data.get(raw_certs_key):
-                bundles.append({
-                    'ca': data['ca'],
-                    'chain': data.get('chain'),
-                    'certs': json.loads(data[raw_certs_key])})
-            elif is_legacy_request:
-                bundles.append({
-                    'ca': data['ca'],
-                    'chain': data.get('chain'),
-                    'certs': {sent['common_name']:
-                              {'cert': data.get(local_name + '.server.cert'),
-                               'key': data.get(local_name + '.server.key')}}})
+            # Note: Bug#2028683 - data may not be available if the certificates
+            # relation hasn't been populated by the providing charm. If no 'ca'
+            # in the data then don't attempt the bundle at all.
+            if data.get('ca'):
+                if data.get(raw_certs_key):
+                    bundles.append({
+                        'ca': data['ca'],
+                        'chain': data.get('chain'),
+                        'certs': json.loads(data[raw_certs_key])
+                    })
+                elif is_legacy_request:
+                    bundles.append({
+                        'ca': data['ca'],
+                        'chain': data.get('chain'),
+                        'certs': {
+                            sent['common_name']: {
+                                'cert': data.get(local_name + '.server.cert'),
+                                'key': data.get(local_name + '.server.key')
+                            }
+                        }
+                    })
 
     return bundles
 
diff --git a/hooks/charmhelpers/contrib/openstack/utils.py b/hooks/charmhelpers/contrib/openstack/utils.py
index f994a3a1..b6171fc0 100644
--- a/hooks/charmhelpers/contrib/openstack/utils.py
+++ b/hooks/charmhelpers/contrib/openstack/utils.py
@@ -2604,6 +2604,23 @@ def get_subordinate_release_packages(os_release, package_type='deb'):
     return SubordinatePackages(install, purge)
 
 
+def get_subordinate_services():
+    """Iterate over subordinate relations and get service information.
+
+    In a similar fashion as with get_subordinate_release_packages(),
+    principle charms can retrieve a list of services advertised by their
+    subordinate charms. This is useful to know about subordinate services when
+    pausing, resuming or upgrading a principle unit.
+
+    :returns: Name of all services advertised by all subordinates
+    :rtype: Set[str]
+    """
+    services = set()
+    for rdata in container_scoped_relation_get('services'):
+        services |= set(json.loads(rdata or '[]'))
+    return services
+
+
 os_restart_on_change = partial(
     pausable_restart_on_change,
     can_restart_now_f=deferred_events.check_and_record_restart_request,
diff --git a/hooks/charmhelpers/fetch/snap.py b/hooks/charmhelpers/fetch/snap.py
index 36d6bce9..7ab7ce3e 100644
--- a/hooks/charmhelpers/fetch/snap.py
+++ b/hooks/charmhelpers/fetch/snap.py
@@ -52,7 +52,7 @@ def _snap_exec(commands):
     :param commands: List commands
     :return: Integer exit code
     """
-    assert type(commands) == list
+    assert isinstance(commands, list)
 
     retry_count = 0
     return_code = None