Use memcache for coordination

src/layer.yaml

@@ -1,4 +1,4 @@
-includes: ['layer:openstack-api', 'interface:ceph-client', 'interface:gnocchi']
+includes: ['layer:openstack-api', 'interface:ceph-client', 'interface:gnocchi', 'interface:memcache']
 options:
   basic:
     use_venv: True

src/lib/charm/openstack/gnocchi.py

@@ -21,6 +21,7 @@ CEPH_CONF = '/etc/ceph/ceph.conf'
 CEPH_POOL_NAME = 'gnocchi'
 
 
+# TODO(jamespage): charms.openstack
 class StorageCephRelationAdapter(adapters.OpenStackRelationAdapter):
 
     """
@@ -36,12 +37,29 @@ class StorageCephRelationAdapter(adapters.OpenStackRelationAdapter):
         to access Ceph.
         """
         hosts = self.relation.mon_hosts()
-        if len(hosts) > 1:
+        if len(hosts) > 0:
             return ','.join(hosts)
         else:
             return None
 
 
+# TODO(jamespage): charms.openstack
+class MemcacheRelationAdapter(adapters.OpenStackRelationAdapter):
+
+    """
+    Adapter for the MemcacheRequires relation interface.
+    """
+
+    interface_type = 'memcache'
+
+    @property
+    def url(self):
+        hosts = self.relation.memcache_hosts()
+        if hosts:
+            return "memcached://{}:11211?timeout=5".format(hosts[0])
+        return None
+
+
 class GnocchiCharmRelationAdapaters(adapters.OpenStackAPIRelationAdapters):
 
     """
@@ -52,6 +70,7 @@ class GnocchiCharmRelationAdapaters(adapters.OpenStackAPIRelationAdapters):
         'storage_ceph': StorageCephRelationAdapter,
         'shared_db': adapters.DatabaseRelationAdapter,
         'cluster': adapters.PeerHARelationAdapter,
+        'coordinator': MemcacheRelationAdapter,
     }
 
 
@@ -86,7 +105,8 @@ class GnocchiCharm(charms_openstack.charm.HAOpenStackCharm):
 
     services = ['gnocchi-metricd', 'apache2']
 
-    required_relations = ['shared-db', 'identity-service', 'storage-ceph']
+    required_relations = ['shared-db', 'identity-service',
+                          'storage-ceph', 'coordinator']
 
     restart_map = {
         GNOCCHI_CONF: services,

src/metadata.yaml

@@ -20,3 +20,5 @@ provides:
 requires:
   storage-ceph:
     interface: ceph-client
+  coordinator:
+    interface: memcache

src/reactive/gnocchi_handlers.py

@@ -29,9 +29,9 @@ charm.use_defaults(
     'update-status')
 
 
+@reactive.when('coordinator.available')
 @reactive.when('shared-db.available')
 @reactive.when('identity-service.available')
-@reactive.when('storage-ceph.available')
 @reactive.when('storage-ceph.pools.available')
 def render_config(*args):
     """Render the configuration for charm when all the interfaces are

src/templates/gnocchi.conf

@@ -17,6 +17,10 @@ url = {{ shared_db.uri }}
 {%- endif %}
 
 [storage]
+{% if coordinator.url -%}
+coordination_url = {{ coordinator.url }}
+{%- endif %}
+
 {% if storage_ceph.key -%}
 driver = ceph
 ceph_pool = gnocchi