set_hostname: When present in metadata, set it before network bringup.

When instance meta-data provides hostname information, run
cc_set_hostname in the init-local or init-net stage before network
comes up.

Prevent an initial DHCP request which leaks the stock cloud-image default
hostname before the meta-data provided hostname was processed.
A leaked cloud-image hostname adversely affects Dynamic DNS which
would reallocate 'ubuntu' hostname in DNS to every instance brought up by
cloud-init. These instances would only update DNS to the cloud-init
configured hostname upon DHCP lease renewal.

This branch extends the get_hostname methods in datasource, cloud and
util to limit results to metadata_only to avoid extra cost of querying
the distro for hostname information if metadata does not provide that
information.

LP: #1746455

1 files changed, 3 insertions, 2 deletions

diff --git a/cloudinit/cloud.py b/cloudinit/cloud.py
index ba616781..6d12c437 100644
--- a/cloudinit/cloud.py
+++ b/cloudinit/cloud.py
@@ -78,8 +78,9 @@ class Cloud(object):
     def get_locale(self):
         return self.datasource.get_locale()
 
-    def get_hostname(self, fqdn=False):
-        return self.datasource.get_hostname(fqdn=fqdn)
+    def get_hostname(self, fqdn=False, metadata_only=False):
+        return self.datasource.get_hostname(
+            fqdn=fqdn, metadata_only=metadata_only)
 
     def device_name_to_device(self, name):
         return self.datasource.device_name_to_device(name)