Skip retry and continued fetch of userdata when NOT_FOUND

When a 404 http code comes back from the fetching of ec2
data, instead of retrying immediatly stop the fetching process
and in the userdata fetching function handle this case as a
special case of no userdata being fetched (an empty string
in this case).

cloudinit/ec2_utils.py

@@ -16,6 +16,7 @@
 #    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 httplib
 from urlparse import (urlparse, urlunparse)
 
 import functools
@@ -23,9 +24,11 @@ import json
 import urllib
 
 from cloudinit import log as logging
+from cloudinit import url_helper
 from cloudinit import util
 
 LOG = logging.getLogger(__name__)
+SKIP_USERDATA_CODES = frozenset([httplib.NOT_FOUND])
 
 
 def maybe_json_object(text):
@@ -138,20 +141,38 @@ class MetadataMaterializer(object):
         return joined
 
 
+def _skip_retry_on_codes(status_codes, request_args, cause):
+    """Returns if a request should retry based on a given set of codes that
+    case retrying to be stopped/skipped.
+    """
+    if cause.code in status_codes:
+        return False
+    return True
+
+
 def get_instance_userdata(api_version='latest',
                           metadata_address='http://169.254.169.254',
                           ssl_details=None, timeout=5, retries=5):
     ud_url = combine_url(metadata_address, api_version)
     ud_url = combine_url(ud_url, 'user-data')
+    user_data = ''
     try:
+        # It is ok for userdata to not exist (thats why we are stopping if
+        # NOT_FOUND occurs) and just in that case returning an empty string.
+        exception_cb = functools.partial(_skip_retry_on_codes,
+                                         SKIP_USERDATA_CODES)
         response = util.read_file_or_url(ud_url,
                                          ssl_details=ssl_details,
                                          timeout=timeout,
-                                         retries=retries)
+                                         retries=retries,
-        return str(response)
+                                         exception_cb=exception_cb)
+        user_data = str(response)
+    except url_helper.UrlError as e:
+        if e.code not in SKIP_USERDATA_CODES:
+            util.logexc(LOG, "Failed fetching userdata from url %s", ud_url)
     except Exception:
         util.logexc(LOG, "Failed fetching userdata from url %s", ud_url)
-        return ''
+    return user_data
 
 
 def get_instance_metadata(api_version='latest',

cloudinit/url_helper.py

@@ -103,7 +103,7 @@ class UrlError(IOError):
 
 def readurl(url, data=None, timeout=None, retries=0, sec_between=1,
             headers=None, headers_cb=None, ssl_details=None,
-            check_status=True, allow_redirects=True):
+            check_status=True, allow_redirects=True, exception_cb=None):
     url = _cleanurl(url)
     req_args = {
         'url': url,
@@ -163,14 +163,13 @@ def readurl(url, data=None, timeout=None, retries=0, sec_between=1,
     # Handle retrying ourselves since the built-in support
     # doesn't handle sleeping between tries...
     for i in range(0, manual_tries):
+        req_args['headers'] = headers_cb(url)
+        filtered_req_args = {}
+        for (k, v) in req_args.items():
+            if k == 'data':
+                continue
+            filtered_req_args[k] = v
         try:
-            req_args['headers'] = headers_cb(url)
-            filtered_req_args = {}
-            for (k, v) in req_args.items():
-                if k == 'data':
-                    continue
-                filtered_req_args[k] = v
-
             LOG.debug("[%s/%s] open '%s' with %s configuration", i,
                       manual_tries, url, filtered_req_args)
 
@@ -196,6 +195,8 @@ def readurl(url, data=None, timeout=None, retries=0, sec_between=1,
                     # ssl exceptions are not going to get fixed by waiting a
                     # few seconds
                     break
+            if exception_cb and not exception_cb(filtered_req_args, e):
+                break
             if i + 1 < manual_tries and sec_between > 0:
                 LOG.debug("Please wait %s seconds while we wait to try again",
                           sec_between)

cloudinit/util.py

@@ -691,7 +691,7 @@ def fetch_ssl_details(paths=None):
 
 def read_file_or_url(url, timeout=5, retries=10,
                      headers=None, data=None, sec_between=1, ssl_details=None,
-                     headers_cb=None):
+                     headers_cb=None, exception_cb=None):
     url = url.lstrip()
     if url.startswith("/"):
         url = "file://%s" % url
@@ -708,7 +708,8 @@ def read_file_or_url(url, timeout=5, retries=10,
                                   headers_cb=headers_cb,
                                   data=data,
                                   sec_between=sec_between,
-                                  ssl_details=ssl_details)
+                                  ssl_details=ssl_details,
+                                  exception_cb=exception_cb)
 
 
 def load_yaml(blob, default=None, allowed=(dict,)):

tests/unittests/test_datasource/test_maas.py

@@ -119,7 +119,8 @@ class TestMAASDataSource(mocker.MockerTestCase):
             mock_request(url, headers=None, timeout=mocker.ANY,
                          data=mocker.ANY, sec_between=mocker.ANY,
                          ssl_details=mocker.ANY, retries=mocker.ANY,
-                         headers_cb=my_headers_cb)
+                         headers_cb=my_headers_cb,
+                         exception_cb=mocker.ANY)
             resp = valid.get(key)
             self.mocker.result(util.StringResponse(resp))
         self.mocker.replay()

tests/unittests/test_ec2_util.py

@@ -33,6 +33,14 @@ class TestEc2Util(helpers.TestCase):
         userdata = eu.get_instance_userdata(self.VERSION, retries=0)
         self.assertEquals('', userdata)
 
+    @hp.activate
+    def test_userdata_fetch_fail_server_not_found(self):
+        hp.register_uri(hp.GET,
+                        'http://169.254.169.254/%s/user-data' % (self.VERSION),
+                        status=404)
+        userdata = eu.get_instance_userdata(self.VERSION)
+        self.assertEquals('', userdata)
+
     @hp.activate
     def test_metadata_fetch_no_keys(self):
         base_url = 'http://169.254.169.254/%s/meta-data' % (self.VERSION)