Azure: Return static fallback address as if failed to find endpoint

The Azure data source helper attempts to use information in the dhcp
lease to find the Wireserver endpoint (IP address). Under some unusual
circumstances, those attempts will fail. This change uses a static
address, known to be always correct in the Azure public and sovereign
clouds, when the helper fails to locate a valid dhcp lease. This
address is not guaranteed to be correct in Azure Stack environments;
it's still best to use the information from the lease whenever possible.

2 files changed, 18 insertions, 5 deletions

diff --git a/cloudinit/sources/helpers/azure.py b/cloudinit/sources/helpers/azure.py
index d3af05ee..82c4c8c4 100755
--- a/cloudinit/sources/helpers/azure.py
+++ b/cloudinit/sources/helpers/azure.py
@@ -20,6 +20,9 @@ from cloudinit.reporting import events
 
 LOG = logging.getLogger(__name__)
 
+# This endpoint matches the format as found in dhcp lease files, since this
+# value is applied if the endpoint can't be found within a lease file
+DEFAULT_WIRESERVER_ENDPOINT = "a8:3f:81:10"
 
 azure_ds_reporter = events.ReportEventStack(
     name="azure-ds",
@@ -297,7 +300,12 @@ class WALinuxAgentShim(object):
     @azure_ds_telemetry_reporter
     def _get_value_from_leases_file(fallback_lease_file):
         leases = []
-        content = util.load_file(fallback_lease_file)
+        try:
+            content = util.load_file(fallback_lease_file)
+        except IOError as ex:
+            LOG.error("Failed to read %s: %s", fallback_lease_file, ex)
+            return None
+
         LOG.debug("content is %s", content)
         option_name = _get_dhcp_endpoint_option_name()
         for line in content.splitlines():
@@ -372,9 +380,9 @@ class WALinuxAgentShim(object):
                           fallback_lease_file)
                 value = WALinuxAgentShim._get_value_from_leases_file(
                     fallback_lease_file)
-
         if value is None:
-            raise ValueError('No endpoint found.')
+            LOG.warning("No lease found; using default endpoint")
+            value = DEFAULT_WIRESERVER_ENDPOINT
 
         endpoint_ip_address = WALinuxAgentShim.get_ip_from_lease_value(value)
         LOG.debug('Azure endpoint found at %s', endpoint_ip_address)
diff --git a/tests/unittests/test_datasource/test_azure_helper.py b/tests/unittests/test_datasource/test_azure_helper.py
index 02556165..bd006aba 100644
--- a/tests/unittests/test_datasource/test_azure_helper.py
+++ b/tests/unittests/test_datasource/test_azure_helper.py
@@ -67,12 +67,17 @@ class TestFindEndpoint(CiTestCase):
         self.networkd_leases.return_value = None
 
     def test_missing_file(self):
-        self.assertRaises(ValueError, wa_shim.find_endpoint)
+        """wa_shim find_endpoint uses default endpoint if leasefile not found
+        """
+        self.assertEqual(wa_shim.find_endpoint(), "168.63.129.16")
 
     def test_missing_special_azure_line(self):
+        """wa_shim find_endpoint uses default endpoint if leasefile is found
+        but does not contain DHCP Option 245 (whose value is the endpoint)
+        """
         self.load_file.return_value = ''
         self.dhcp_options.return_value = {'eth0': {'key': 'value'}}
-        self.assertRaises(ValueError, wa_shim.find_endpoint)
+        self.assertEqual(wa_shim.find_endpoint(), "168.63.129.16")
 
     @staticmethod
     def _build_lease_content(encoded_address):