Merge pull request #16 from chuckbutler/minimum-juju-version

is_leader requires juju 1.22.0 or better

README.md

@@ -51,10 +51,17 @@ Health of the cluster can be checked by verified via juju actions
     juju action fetch <uuid>
 
 
+## Usage Caveats
+
+This charm requires Leader Election, which is a feature of Juju >= 1.23.2. The
+charm will panic and refuse to continue if the leader_election binary is not
+found. Please take care when deploying this charm on older versions of Juju.
+
 ## Credits
 
 The etcd charm was originally written by Kapil Thangavelu ([@kapilt](https://github.com/kapilt)).
 
+
 #### Mantainers: 
 
 The kubernetes team maintains this charm:

hooks/hooks.py

@@ -16,11 +16,18 @@
 hook_data = unitdata.HookData()
 db = unitdata.kv()
 
-leader_status = check_output(['is-leader']).rstrip() != "False"
 private_address = hookenv.unit_get('private-address')
 public_address = hookenv.unit_get('private-address')
 unit_name = environ['JUJU_UNIT_NAME'].replace('/', '')
 
+try:
+    leader_status = hookenv.is_leader()
+except NotImplementedError:
+    hookenv.log('This charm requires Leader Election. Juju >= 1.23.2.'
+                ' Leader election binary not found, Panic and exit!',
+                'CRITICAL')
+    sys.exit(1)
+
 
 @hooks.hook('config-changed')
 def config_changed():