wrap boto.utils.get_instance_metadata to ensure non-lazy loading

newer versions of boto lazily load the metadata from the ec2
metadata service. Here, we:

1. Add a ec2_utils module that checks which version of boto is being used and
   under the right versions the metadata dictionary will be expanded.
2. Use this new ec2_utils module in the cloudstack and ec2
   datasources as there entrypoints into boto.
3. Add a dependency on python-pkg-resources (from pkg_resources import
   parse_version) to determine the boto version.

ChangeLog

@@ -23,6 +23,9 @@
  - Fix the merging of group configuration when that group configuration is a
    dict => members. [revno 707]
  - add yum_add_repo configuration module for adding additional yum repos
+ - work around the lazy loading of get_instance_metadata in boto >= 2.6.0
+   by fully walking the dictionary. (LP: #1068801)
+   Added dependency on distribute's python-pkg-resources
 0.7.0:
  - add a 'exception_cb' argument to 'wait_for_url'.  If provided, this
    method will be called back with the exception received and the message.

cloudinit/ec2_utils.py

@@ -0,0 +1,70 @@
+# vi: ts=4 expandtab
+#
+#    Copyright (C) 2012 Yahoo! Inc.
+#
+#    Author: Joshua Harlow <harlowja@yahoo-inc.com>
+#
+#    This program is free software: you can redistribute it and/or modify
+#    it under the terms of the GNU General Public License version 3, as
+#    published by the Free Software Foundation.
+#
+#    This program is distributed in the hope that it will be useful,
+#    but WITHOUT ANY WARRANTY; without even the implied warranty of
+#    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+#    GNU General Public License for more details.
+#
+#    You should have received a copy of the GNU General Public License
+#    along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+import pkg_resources
+from pkg_resources import parse_version
+
+import cloudinit.util as util
+import cloudinit.url_helper as uh
+
+import boto.utils as boto_utils
+
+# Versions of boto >= 2.6.0 try to lazily load
+# the metadata backing, which doesn't work so well
+# in cloud-init especially since the metadata is
+# serialized and actions are performed where the
+# metadata server may be blocked (thus the datasource
+# will start failing) resulting in url exceptions
+# when fields that do exist (or would have existed)
+# do not exist due to the blocking that occurred.
+
+BOTO_LAZY = False
+try:
+    _boto_lib = pkg_resources.get_distribution('boto')
+    if _boto_lib.parsed_version > parse_version("2.5.2"):
+        BOTO_LAZY = True
+except pkg_resources.DistributionNotFound:
+    pass
+
+
+def _unlazy_dict(mp):
+    if not isinstance(mp, (dict)):
+        return mp
+    if not BOTO_LAZY:
+        return mp
+    for (k, v) in mp.items():
+        _unlazy_dict(v)
+    return mp
+
+
+def get_instance_userdata(api_version, metadata_address):
+    # Note: boto.utils.get_instance_metadata returns '' for empty string
+    # so the change from non-true to '' is not specifically necessary, but
+    # this way cloud-init will get consistent behavior even if boto changed
+    # in the future to return a None on "no user-data provided".
+    ud = boto_utils.get_instance_userdata(api_version, None, metadata_address)
+    if not ud:
+        ud = ''
+    return ud
+
+
+def get_instance_metadata(api_version, metadata_address):
+    metadata = boto_utils.get_instance_metadata(api_version, metadata_address)
+    if not isinstance(metadata, (dict)):
+        metadata = {}
+    return _unlazy_dict(metadata)

cloudinit/sources/DataSourceCloudStack.py

@@ -26,8 +26,7 @@ from struct import pack
 import os
 import time
 
-import boto.utils as boto_utils
-
+from cloudinit import ec2_utils as ec2
 from cloudinit import log as logging
 from cloudinit import sources
 from cloudinit import url_helper as uhelp
@@ -116,10 +115,10 @@ class DataSourceCloudStack(sources.DataSource):
             if not self.wait_for_metadata_service():
                 return False
             start_time = time.time()
-            self.userdata_raw = boto_utils.get_instance_userdata(self.api_ver,
-                None, self.metadata_address)
-            self.metadata = boto_utils.get_instance_metadata(self.api_ver,
-                self.metadata_address)
+            self.userdata_raw = ec2.get_instance_userdata(self.api_ver,
+                                                          self.metadata_address)
+            self.metadata = ec2.get_instance_metadata(self.api_ver,
+                                                      self.metadata_address)
             LOG.debug("Crawl of metadata service took %s seconds",
                       int(time.time() - start_time))
             return True

cloudinit/sources/DataSourceEc2.py

@@ -23,8 +23,7 @@
 import os
 import time
 
-import boto.utils as boto_utils
-
+from cloudinit import ec2_utils as ec2
 from cloudinit import log as logging
 from cloudinit import sources
 from cloudinit import url_helper as uhelp
@@ -65,10 +64,10 @@ class DataSourceEc2(sources.DataSource):
             if not self.wait_for_metadata_service():
                 return False
             start_time = time.time()
-            self.userdata_raw = boto_utils.get_instance_userdata(self.api_ver,
-                None, self.metadata_address)
-            self.metadata = boto_utils.get_instance_metadata(self.api_ver,
-                self.metadata_address)
+            self.userdata_raw = ec2.get_instance_userdata(self.api_ver,
+                                                          self.metadata_address)
+            self.metadata = ec2.get_instance_metadata(self.api_ver,
+                                                      self.metadata_address)
             LOG.debug("Crawl of metadata service took %s seconds",
                        int(time.time() - start_time))
             return True

packages/debian/control.in

@@ -19,6 +19,7 @@ Standards-Version: 3.9.3
 Package: cloud-init
 Architecture: all
 Depends: cloud-utils,
+         distribute,
          procps,
          python,
 #for $r in $requires