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, 12 insertions, 5 deletions

diff --git a/cloudinit/util.py b/cloudinit/util.py
index 083a8efe..4504f053 100644
--- a/cloudinit/util.py
+++ b/cloudinit/util.py
@@ -1025,9 +1025,16 @@ def dos2unix(contents):
     return contents.replace('\r\n', '\n')
 
 
-def get_hostname_fqdn(cfg, cloud):
-    # return the hostname and fqdn from 'cfg'.  If not found in cfg,
-    # then fall back to data from cloud
+def get_hostname_fqdn(cfg, cloud, metadata_only=False):
+    """Get hostname and fqdn from config if present and fallback to cloud.
+
+    @param cfg: Dictionary of merged user-data configuration (from init.cfg).
+    @param cloud: Cloud instance from init.cloudify().
+    @param metadata_only: Boolean, set True to only query cloud meta-data,
+        returning None if not present in meta-data.
+    @return: a Tuple of strings <hostname>, <fqdn>. Values can be none when
+        metadata_only is True and no cfg or metadata provides hostname info.
+    """
     if "fqdn" in cfg:
         # user specified a fqdn.  Default hostname then is based off that
         fqdn = cfg['fqdn']
@@ -1041,11 +1048,11 @@ def get_hostname_fqdn(cfg, cloud):
         else:
             # no fqdn set, get fqdn from cloud.
             # get hostname from cfg if available otherwise cloud
-            fqdn = cloud.get_hostname(fqdn=True)
+            fqdn = cloud.get_hostname(fqdn=True, metadata_only=metadata_only)
             if "hostname" in cfg:
                 hostname = cfg['hostname']
             else:
-                hostname = cloud.get_hostname()
+                hostname = cloud.get_hostname(metadata_only=metadata_only)
     return (hostname, fqdn)