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, 25 insertions, 0 deletions

diff --git a/cloudinit/cmd/main.py b/cloudinit/cmd/main.py
index fcddd75c..3f2dbb93 100644
--- a/cloudinit/cmd/main.py
+++ b/cloudinit/cmd/main.py
@@ -40,6 +40,7 @@ from cloudinit.settings import (PER_INSTANCE, PER_ALWAYS, PER_ONCE,
 
 from cloudinit import atomic_helper
 
+from cloudinit.config import cc_set_hostname
 from cloudinit.dhclient_hook import LogDhclient
 
 
@@ -352,6 +353,11 @@ def main_init(name, args):
     LOG.debug("[%s] %s will now be targeting instance id: %s. new=%s",
               mode, name, iid, init.is_new_instance())
 
+    if mode == sources.DSMODE_LOCAL:
+        # Before network comes up, set any configured hostname to allow
+        # dhcp clients to advertize this hostname to any DDNS services
+        # LP: #1746455.
+        _maybe_set_hostname(init, stage='local', retry_stage='network')
     init.apply_network_config(bring_up=bool(mode != sources.DSMODE_LOCAL))
 
     if mode == sources.DSMODE_LOCAL:
@@ -368,6 +374,7 @@ def main_init(name, args):
     init.setup_datasource()
     # update fully realizes user-data (pulling in #include if necessary)
     init.update()
+    _maybe_set_hostname(init, stage='init-net', retry_stage='modules:config')
     # Stage 7
     try:
         # Attempt to consume the data per instance.
@@ -681,6 +688,24 @@ def status_wrapper(name, args, data_d=None, link_d=None):
     return len(v1[mode]['errors'])
 
 
+def _maybe_set_hostname(init, stage, retry_stage):
+    """Call set-hostname if metadata, vendordata or userdata provides it.
+
+    @param stage: String representing current stage in which we are running.
+    @param retry_stage: String represented logs upon error setting hostname.
+    """
+    cloud = init.cloudify()
+    (hostname, _fqdn) = util.get_hostname_fqdn(
+        init.cfg, cloud, metadata_only=True)
+    if hostname:  # meta-data or user-data hostname content
+        try:
+            cc_set_hostname.handle('set-hostname', init.cfg, cloud, LOG, None)
+        except cc_set_hostname.SetHostnameError as e:
+            LOG.debug(
+                'Failed setting hostname in %s stage. Will'
+                ' retry in %s stage. Error: %s.', stage, retry_stage, str(e))
+
+
 def main_features(name, args):
     sys.stdout.write('\n'.join(sorted(version.FEATURES)) + '\n')