Example of hostname

config.yaml

@@ -0,0 +1,6 @@
+options:
+  hostname:
+    type: string
+    default: 
+    description: Override hostname of machine, when empty uses default machine hostname
+

reactive/ubuntu.py

@@ -1,6 +1,8 @@
 
-from charms.reactive import when_not, set_state
-from charmhelpers.core.hookenv import status_set, application_version_set
+import subprocess
+
+from charms.reactive import when, when_not, set_state
+from charmhelpers.core.hookenv import status_set, application_version_set, config
 from charmhelpers.core.host import lsb_release
 
 
@@ -9,3 +11,15 @@ def status_ubuntu():
     status_set('active', 'ready')
     application_version_set(lsb_release()['DISTRIB_RELEASE'])
     set_state('ubuntu.ready')
+
+
+@when('config.changed.hostname')
+def update_hostname():
+    hostname = config().get('hostname')
+    if not hostname:
+        return
+
+    with open('/etc/hostname', 'w') as f:
+        f.write(hostname)
+
+    subprocess.check_call(['hostname', hostname])