Add support for publishing host keys to GCE guest attributes

This adds an empty publish_host_keys() method to the default datasource
that is called by cc_ssh.py. This feature can be controlled by the
'ssh_publish_hostkeys' config option. It is enabled by default but can
be disabled by setting 'enabled' to false. Also, a blacklist of key
types is supported.

In addition, this change implements ssh_publish_hostkeys() for the GCE
datasource, attempting to write the hostkeys to the instance's guest
attributes. Using these hostkeys for ssh connections is currently
supported by the alpha version of Google's 'gcloud' command-line tool.

(On Google Compute Engine, this feature will be enabled by setting the
'enable-guest-attributes' metadata key to 'true' for the
project/instance that you would like to use this feature for. When
connecting to the instance for the first time using 'gcloud compute ssh'
the hostkeys will be read from the guest attributes for the instance and
written to the user's local known_hosts file for Google Compute Engine
instances.)

1 files changed, 20 insertions, 2 deletions

diff --git a/cloudinit/sources/DataSourceGCE.py b/cloudinit/sources/DataSourceGCE.py
index d8162623..6cbfbbac 100644
--- a/cloudinit/sources/DataSourceGCE.py
+++ b/cloudinit/sources/DataSourceGCE.py
@@ -18,10 +18,13 @@ LOG = logging.getLogger(__name__)
 MD_V1_URL = 'http://metadata.google.internal/computeMetadata/v1/'
 BUILTIN_DS_CONFIG = {'metadata_url': MD_V1_URL}
 REQUIRED_FIELDS = ('instance-id', 'availability-zone', 'local-hostname')
+GUEST_ATTRIBUTES_URL = ('http://metadata.google.internal/computeMetadata/'
+                        'v1/instance/guest-attributes')
+HOSTKEY_NAMESPACE = 'hostkeys'
+HEADERS = {'Metadata-Flavor': 'Google'}
 
 
 class GoogleMetadataFetcher(object):
-    headers = {'Metadata-Flavor': 'Google'}
 
     def __init__(self, metadata_address):
         self.metadata_address = metadata_address
@@ -32,7 +35,7 @@ class GoogleMetadataFetcher(object):
             url = self.metadata_address + path
             if is_recursive:
                 url += '/?recursive=True'
-            resp = url_helper.readurl(url=url, headers=self.headers)
+            resp = url_helper.readurl(url=url, headers=HEADERS)
         except url_helper.UrlError as exc:
             msg = "url %s raised exception %s"
             LOG.debug(msg, path, exc)
@@ -90,6 +93,10 @@ class DataSourceGCE(sources.DataSource):
         public_keys_data = self.metadata['public-keys-data']
         return _parse_public_keys(public_keys_data, self.default_user)
 
+    def publish_host_keys(self, hostkeys):
+        for key in hostkeys:
+            _write_host_key_to_guest_attributes(*key)
+
     def get_hostname(self, fqdn=False, resolve_ip=False, metadata_only=False):
         # GCE has long FDQN's and has asked for short hostnames.
         return self.metadata['local-hostname'].split('.')[0]
@@ -103,6 +110,17 @@ class DataSourceGCE(sources.DataSource):
         return self.availability_zone.rsplit('-', 1)[0]
 
 
+def _write_host_key_to_guest_attributes(key_type, key_value):
+    url = '%s/%s/%s' % (GUEST_ATTRIBUTES_URL, HOSTKEY_NAMESPACE, key_type)
+    key_value = key_value.encode('utf-8')
+    resp = url_helper.readurl(url=url, data=key_value, headers=HEADERS,
+                              request_method='PUT', check_status=False)
+    if resp.ok():
+        LOG.debug('Wrote %s host key to guest attributes.',  key_type)
+    else:
+        LOG.debug('Unable to write %s host key to guest attributes.', key_type)
+
+
 def _has_expired(public_key):
     # Check whether an SSH key is expired. Public key input is a single SSH
     # public key in the GCE specific key format documented here: