Fixed ambiguous error message raised when resolving region from IMDS

.changes/next-release/bugfix-IMDS-70100.json

@@ -0,0 +1,5 @@
+{
+  "type": "bugfix",
+  "category": "IMDS",
+  "description": "Fixed ambiguous error raised when failing to resolve a region from IMDS."
+}

awscli/utils.py

@@ -26,6 +26,7 @@
 from botocore.useragent import UserAgentComponent
 from botocore.utils import resolve_imds_endpoint_mode
 from botocore.utils import IMDSFetcher
+from botocore.utils import BadIMDSRequestError
 from botocore.configprovider import BaseProvider
 
 logger = logging.getLogger(__name__)
@@ -171,9 +172,17 @@ def retrieve_region(self):
             region = self._get_region()
             return region
         except self._RETRIES_EXCEEDED_ERROR_CLS:
-            logger.debug("Max number of attempts exceeded (%s) when "
-                         "attempting to retrieve data from metadata service.",
-                         self._num_attempts)
+            logger.debug(
+                "Max number of attempts exceeded (%s) when "
+                "attempting to retrieve data from metadata service.",
+                self._num_attempts
+            )
+        except BadIMDSRequestError as e:
+            logger.debug(
+                "Failed to retrieve a region from IMDS. "
+                "Region detection may not be supported from this endpoint: "
+                "%s", e.request.url
+            )
         return None
 
     def _get_region(self):

tests/unit/test_utils.py

@@ -348,8 +348,8 @@ def add_get_region_imds_response(self, region=None):
             region = self._region
         self.add_imds_response(body=region.encode('utf-8'))
 
-    def add_imds_token_response(self):
-        self.add_imds_response(status_code=200, body=b'token')
+    def add_imds_token_response(self, status_code=200, body=b'token'):
+        self.add_imds_response(status_code=status_code, body=body)
 
     def add_imds_connection_error(self, exception):
         self._imds_responses.append(exception)
@@ -461,6 +461,19 @@ def test_exhaust_retries_on_region_request(self):
             num_attempts=1).retrieve_region()
         self.assertEqual(result, None)
 
+    def test_400_response_returns_none(self):
+        # Response from endpoint providing a 400 during
+        # token resolution implies the (likely third-party)
+        # endpoint may not support IMDS v2.
+        #
+        # We treat this as terminal because retries will
+        # unnecessarily delay failure for a incompatible endpoint.
+        self.add_imds_token_response(body=b"Bad Request", status_code=400)
+        result = InstanceMetadataRegionFetcher(
+            num_attempts=2
+        ).retrieve_region()
+        self.assertEqual(result, None)
+
 
 class TestIMDSRegionProvider(BaseIMDSRegionTest):
     def assert_does_provide_expected_value(self, fetcher_region=None,