Fix IMDS region resolution in Local Zones

.changes/next-release/bugfix-IMDS-51328.json

@@ -0,0 +1,5 @@
+{
+  "type": "bugfix",
+  "category": "IMDS",
+  "description": "Fixes region resolution from IMDS in Local Zones by reading the region directly instead of deriving it from the availability zone."
+}

awscli/utils.py

@@ -163,7 +163,7 @@ def _create_fetcher(self):
 
 
 class InstanceMetadataRegionFetcher(IMDSFetcher):
-    _URL_PATH = 'latest/meta-data/placement/availability-zone/'
+    _URL_PATH = 'latest/meta-data/placement/region'
 
     def retrieve_region(self):
         """Get the current region from the instance metadata service.
@@ -204,9 +204,7 @@ def _get_region(self):
             retry_func=self._default_retry,
             token=token,
         )
-        availability_zone = response.text
-        region = availability_zone[:-1]
-        return region
+        return response.text
 
 
 def split_on_commas(value):

scripts/new-change

@@ -29,7 +29,7 @@ You'll see this template::
 Fill in the appropriate values, save and exit the editor.
 Make sure to commit these changes as part of your pull request.
 
-If, when your editor is open, you decide don't don't want to add a changelog
+If, when your editor is open, you decide you don't want to add a changelog
 entry, save an empty file and no entry will be generated.
 
 You can then use the ``scripts/render-change`` to generate the

tests/functional/test_clidriver.py

@@ -66,9 +66,8 @@ def test_imds_region_is_used_as_fallback_wo_v2_support(self):
         # First response should be from the IMDS server for security token
         # if server supports IMDSv1 only there will be no response for token
         self.add_response(None)
-        # Then another response from the IMDS server for an availability
-        # zone.
-        self.add_response(b'us-mars-2a')
+        # Then another response from the IMDS server for the region.
+        self.add_response(b'us-mars-2')
         # Once a region is fetched form the IMDS server we need to mock an
         # XML response from ec2 so that the CLI driver doesn't throw an error
         # during parsing.
@@ -84,9 +83,8 @@ def test_imds_region_is_used_as_fallback_with_v2_support(self):
         # First response should be from the IMDS server for security token
         # if server supports IMDSv2 it'll return token
         self.add_response(b'token')
-        # Then another response from the IMDS server for an availability
-        # zone.
-        self.add_response(b'us-mars-2a')
+        # Then another response from the IMDS server for the region.
+        self.add_response(b'us-mars-2')
         # Once a region is fetched form the IMDS server we need to mock an
         # XML response from ec2 so that the CLI driver doesn't throw an error
         # during parsing.

tests/unit/test_utils.py

@@ -399,7 +399,7 @@ def setUp(self):
         self._send = self._urllib3_patch.start()
         self._imds_responses = []
         self._send.side_effect = self.get_imds_response
-        self._region = 'us-mars-1a'
+        self._region = 'us-mars-1'
         self.environ = {}
         self.environ_patch = mock.patch('os.environ', self.environ)
         self.environ_patch.start()
@@ -473,6 +473,26 @@ def test_includes_user_agent_header(self):
         headers = self._send.call_args[0][0].headers
         self.assertEqual(headers['User-Agent'], user_agent)
 
+    def test_requests_region_from_placement_region(self):
+        self.add_imds_token_response()
+        self.add_get_region_imds_response()
+
+        InstanceMetadataRegionFetcher().retrieve_region()
+
+        url = self._send.call_args[0][0].url
+        self.assertTrue(url.endswith('latest/meta-data/placement/region'))
+
+    def test_local_zone_returns_parent_region(self):
+        # In a Local Zone the availability zone is e.g. us-east-1-atl-2a,
+        # so the region has to come from placement/region rather than
+        # being derived from the availability zone.
+        self.add_imds_token_response()
+        self.add_get_region_imds_response(region='us-east-1')
+
+        result = InstanceMetadataRegionFetcher().retrieve_region()
+
+        self.assertEqual(result, 'us-east-1')
+
     def test_non_200_response_for_region_is_retried(self):
         # Response for role name that have a non 200 status code should
         # be retried.