Add environment variable to override endpoint_url (boto#2099)

boto3/session.py

@@ -255,6 +255,12 @@ def client(self, service_name, region_name=None, api_version=None,
         :return: Service client instance
 
         """
+        if endpoint_url is None:
+            try:
+                endpoint_url = os.environ["AWS_ENDPOINT_URL"]
+            except KeyError:
+                pass
+
         return self._session.create_client(
             service_name, region_name=region_name, api_version=api_version,
             use_ssl=use_ssl, verify=verify, endpoint_url=endpoint_url,

docs/source/guide/configuration.rst

@@ -131,6 +131,9 @@ Configurations can be set through the use of system-wide environment variables.
     Specifies the types of retries the SDK will use.  For more information,
     see the ``retry_mode`` configuration file section.
 
+``AWS_ENDPOINT_URL``
+    Overrides the default AWS endpoint_url.  Useful when testing with localstack or minio, for example.
+
 Using a configuration file
 -------------------
 

tests/unit/test_endpoint_url.py

@@ -0,0 +1,24 @@
+import os
+import unittest
+
+import boto3
+
+class TestEndpointUrl(unittest.TestCase):
+    def test_default_session_does_not_require_endpoint_url_env_var(self):
+        boto3.setup_default_session(
+            aws_access_key_id='key',
+            aws_secret_access_key='secret')
+        client = boto3.DEFAULT_SESSION.client('s3')
+        self.assertTrue(client._endpoint.host.endswith("amazonaws.com"),
+            "AWS_ENDPOINT_URL env var should not be required")
+
+    def test_default_session_uses_endpoint_url_env_var(self):
+        ENDPOINT_URL = "http://endpoint.url"
+        os.environ["AWS_ENDPOINT_URL"] = ENDPOINT_URL
+        boto3.setup_default_session(
+            aws_access_key_id='key',
+            aws_secret_access_key='secret')
+        client = boto3.DEFAULT_SESSION.client('s3')
+        self.assertTrue(client._endpoint.host == ENDPOINT_URL, 'AWS_ENDPOINT_URL env var not used when set')
+
+# eof