Give precedence to region override over config (#8997)

viren-nadkarni · web-flow · commit 4548bf479b6e · 2023-08-31T13:30:16.000+05:30
diff --git a/localstack/aws/connect.py b/localstack/aws/connect.py
@@ -18,6 +18,7 @@
 
 from localstack import config as localstack_config
 from localstack.constants import (
+    AWS_REGION_US_EAST_1,
     INTERNAL_AWS_ACCESS_KEY_ID,
     INTERNAL_AWS_SECRET_ACCESS_KEY,
     MAX_POOL_CONNECTIONS,
@@ -465,6 +466,14 @@ def get_client(
         else:
             config = self._config.merge(config)
 
+        # Boto has an odd behaviour when using a non-default (any other region than us-east-1) in config
+        # If the region in arg is non-default, it gives the arg the precedence
+        # But if the region in arg is default (us-east-1), it gives precedence to one in config
+        # Below: always give precedence to arg region
+        if config and config.region_name != AWS_REGION_US_EAST_1:
+            if region_name == AWS_REGION_US_EAST_1:
+                config = config.merge(Config(region_name=region_name))
+
         endpoint_url = endpoint_url or get_local_service_url(service_name)
         if service_name == "s3":
             if re.match(r"https?://localhost(:[0-9]+)?", endpoint_url):
diff --git a/tests/unit/aws/test_connect.py b/tests/unit/aws/test_connect.py
@@ -1,6 +1,7 @@
 from unittest.mock import ANY, MagicMock, patch
 
 import boto3
+import botocore
 import pytest
 
 from localstack.aws.api import RequestContext
@@ -426,3 +427,16 @@ def echo_request_handler(_: HandlerChain, context: RequestContext, response: Res
         clients.lambda_.list_functions()
 
         assert test_params == expected_result
+
+    def test_region_override(self):
+        # Boto has an odd behaviour when using a non-default (any other region than us-east-1) in config
+        # If the region in arg is non-default, it gives the arg the precedence
+        # But if the region in arg is default (us-east-1), it gives precedence to one in config
+        # This test asserts that this behaviour is handled by client factories and always give precedence to arg region
+
+        factory = ExternalClientFactory()
+
+        config = botocore.config.Config(region_name="eu-north-1")
+
+        assert factory(region_name="us-east-1", config=config).s3.meta.region_name == "us-east-1"
+        assert factory(region_name="us-west-1", config=config).s3.meta.region_name == "us-west-1"
