Switch default transport to unicast

Unicast is generally alot more reliable and is guaranteed to work
in all network configurations unlike multicast.

Optimize context build for unicast configuration - its possible to
build the corosync cluster prior to the principle charm presenting
multicast only configuration options.

Change-Id: I7c4f559325234401a7b6f7aa26114349d07817ad

config.yaml

@@ -15,25 +15,32 @@ options:
       order for this charm to function correctly, the privacy extension must be
       disabled and a non-temporary address must be configured/available on
       your network interface.
+  corosync_transport:
+    type: string
+    default: "unicast"
+    description: |
+      Two supported modes are multicast (udp) or unicast (udpu)
   corosync_mcastaddr:
     type: string
     default: 226.94.1.1
     description: |
       Multicast IP address to use for exchanging messages over the network.
       If multiple clusters are on the same bindnetaddr network, this value
-      can be changed.
+      can be changed.  Only used when corosync_transport = multicast.
   corosync_bindiface:
     type: string
     default:
     description: |
       Default network interface on which HA cluster will bind to communication
-      with the other members of the HA Cluster.
+      with the other members of the HA Cluster.  Defaults to the network
+      interface hosting the units private-address.  Only used when
+      corosync_transport = multicast.
   corosync_mcastport:
     type: int
     default:
     description: |
       Default multicast port number that will be used to communicate between
-      HA Cluster nodes.
+      HA Cluster nodes. Only used when corosync_transport = multicast.
   corosync_key:
     type: string
     default: "64RxJNcCkwo8EJYBsaacitUvbQp5AW4YolJi5/2urYZYp2jfLxY+3IUCOaAUJHPle4Yqfy+WBXO0I/6ASSAjj9jaiHVNaxmVhhjcmyBqy2vtPf+m+0VxVjUXlkTyYsODwobeDdO3SIkbIABGfjLTu29yqPTsfbvSYr6skRb9ne0="
@@ -104,11 +111,6 @@ options:
       Specifies the corosync.conf network mtu. If unset, the default
       corosync.conf value is used (currently 1500). See 'man corosync.conf' for
       detailed information on this config option.
-  corosync_transport:
-    type: string
-    default: "multicast"
-    description: |
-      Two supported modes are multicast (udp) or unicast (udpu)
   nagios_context:
     default: "juju"
     type: string

hooks/utils.py

@@ -212,18 +212,25 @@ def get_corosync_conf():
         ip_version = 'ipv4'
         bindnetaddr = get_network_address
 
+    transport = get_transport()
+
     # NOTE(jamespage) use local charm configuration over any provided by
     # principle charm
     conf = {
-        'corosync_bindnetaddr':
-        bindnetaddr(config('corosync_bindiface')),
-        'corosync_mcastport': config('corosync_mcastport'),
-        'corosync_mcastaddr': config('corosync_mcastaddr'),
         'ip_version': ip_version,
         'ha_nodes': get_ha_nodes(),
-        'transport': get_transport(),
+        'transport': transport,
     }
 
+    # NOTE(jamespage): only populate multicast configuration if udp is
+    #                  configured
+    if transport == 'udp':
+        conf.update({
+            'corosync_bindnetaddr': bindnetaddr(config('corosync_bindiface')),
+            'corosync_mcastport': config('corosync_mcastport'),
+            'corosync_mcastaddr': config('corosync_mcastaddr')
+        })
+
     if config('prefer-ipv6'):
         conf['nodeid'] = get_corosync_id(local_unit())
 
@@ -241,18 +248,24 @@ def get_corosync_conf():
     conf = {}
     for relid in relation_ids('ha'):
         for unit in related_units(relid):
-            bindiface = relation_get('corosync_bindiface',
-                                     unit, relid)
             conf = {
-                'corosync_bindnetaddr': bindnetaddr(bindiface),
-                'corosync_mcastport': relation_get('corosync_mcastport',
-                                                   unit, relid),
-                'corosync_mcastaddr': config('corosync_mcastaddr'),
                 'ip_version': ip_version,
                 'ha_nodes': get_ha_nodes(),
-                'transport': get_transport(),
+                'transport': transport,
             }
 
+            # NOTE(jamespage): only populate multicast configuration if udpu is
+            #                  configured
+            if transport == 'udp':
+                bindiface = relation_get('corosync_bindiface',
+                                         unit, relid)
+                conf.update({
+                    'corosync_bindnetaddr': bindnetaddr(bindiface),
+                    'corosync_mcastport': relation_get('corosync_mcastport',
+                                                       unit, relid),
+                    'corosync_mcastaddr': config('corosync_mcastaddr'),
+                })
+
             if config('prefer-ipv6'):
                 conf['nodeid'] = get_corosync_id(local_unit())