fix: load_sagemaker_config should lazy initialize a default S3 resource

src/sagemaker/config/config.py

@@ -43,17 +43,10 @@
 ENV_VARIABLE_ADMIN_CONFIG_OVERRIDE = "SAGEMAKER_ADMIN_CONFIG_OVERRIDE"
 ENV_VARIABLE_USER_CONFIG_OVERRIDE = "SAGEMAKER_USER_CONFIG_OVERRIDE"
 
-_BOTO_SESSION = boto3.DEFAULT_SESSION or boto3.Session()
-# The default Boto3 S3 Resource. This is constructed from the default Boto3 session. This will be
-# used to fetch SageMakerConfig from S3. Users can override this by passing their own S3 Resource
-# as the constructor parameter for SageMakerConfig.
-_DEFAULT_S3_RESOURCE = _BOTO_SESSION.resource("s3")
 S3_PREFIX = "s3://"
 
 
-def load_sagemaker_config(
-    additional_config_paths: List[str] = None, s3_resource=_DEFAULT_S3_RESOURCE
-) -> dict:
+def load_sagemaker_config(additional_config_paths: List[str] = None, s3_resource=None) -> dict:
     """Loads config files and merges them.
 
     By default, this method first searches for config files in the default locations
@@ -95,8 +88,9 @@ def load_sagemaker_config(
 
             Note: S3 URI follows the format ``s3://<bucket>/<Key prefix>``
         s3_resource (boto3.resource("s3")): The Boto3 S3 resource. This is used to fetch
-            config files from S3. If it is not provided, this method creates a default S3 resource.
-            See `Boto3 Session documentation <https://boto3.amazonaws.com/v1/documentation/api\
+            config files from S3. If it is not provided but config files are present in S3,
+            this method creates a default S3 resource. See `Boto3 Session documentation
+            <https://boto3.amazonaws.com/v1/documentation/api\
             /latest/reference/core/session.html#boto3.session.Session.resource>`__.
             This argument is not needed if the config files are present in the local file system.
     """
@@ -161,7 +155,15 @@ def _load_config_from_file(file_path: str) -> dict:
 def _load_config_from_s3(s3_uri, s3_resource_for_config) -> dict:
     """Placeholder docstring"""
     if not s3_resource_for_config:
-        raise RuntimeError("No S3 client found. Provide a S3 client to load the config file.")
+        # Constructing a default Boto3 S3 Resource from a default Boto3 session.
+        boto_session = boto3.DEFAULT_SESSION or boto3.Session()
+        boto_region_name = boto_session.region_name
+        if boto_region_name is None:
+            raise ValueError(
+                "Must setup local AWS configuration with a region supported by SageMaker."
+            )
+        s3_resource_for_config = boto_session.resource("s3", region_name=boto_region_name)
+
     logger.debug("Fetching config file from the S3 URI: %s", s3_uri)
     inferred_s3_uri = _get_inferred_s3_uri(s3_uri, s3_resource_for_config)
     parsed_url = urlparse(inferred_s3_uri)

src/sagemaker/local/local_session.py

@@ -674,22 +674,19 @@ def _initialize(
         self.sagemaker_client = LocalSagemakerClient(self)
         self.sagemaker_runtime_client = LocalSagemakerRuntimeClient(self.config)
         self.local_mode = True
-        sagemaker_config = kwargs.get("sagemaker_config", None)
-        if sagemaker_config:
-            validate_sagemaker_config(sagemaker_config)
 
         if self.s3_endpoint_url is not None:
             self.s3_resource = boto_session.resource("s3", endpoint_url=self.s3_endpoint_url)
             self.s3_client = boto_session.client("s3", endpoint_url=self.s3_endpoint_url)
-            self.sagemaker_config = (
-                sagemaker_config
-                if sagemaker_config
-                else load_sagemaker_config(s3_resource=self.s3_resource)
-            )
+
+        sagemaker_config = kwargs.get("sagemaker_config", None)
+        if sagemaker_config:
+            validate_sagemaker_config(sagemaker_config)
+            self.sagemaker_config = sagemaker_config
         else:
-            self.sagemaker_config = (
-                sagemaker_config if sagemaker_config else load_sagemaker_config()
-            )
+            # self.s3_resource might be None. If it is None, load_sagemaker_config will
+            # create a default S3 resource, but only if it needs to fetch from S3
+            self.sagemaker_config = load_sagemaker_config(s3_resource=self.s3_resource)
 
         sagemaker_config_file = os.path.join(os.path.expanduser("~"), ".sagemaker", "config.yaml")
         if os.path.exists(sagemaker_config_file):

src/sagemaker/session.py

@@ -266,15 +266,14 @@ def _initialize(
         prepend_user_agent(self.sagemaker_metrics_client)
 
         self.local_mode = False
+
         if sagemaker_config:
             validate_sagemaker_config(sagemaker_config)
             self.sagemaker_config = sagemaker_config
         else:
-            if self.s3_resource is None:
-                s3 = self.boto_session.resource("s3", region_name=self.boto_region_name)
-            else:
-                s3 = self.s3_resource
-            self.sagemaker_config = load_sagemaker_config(s3_resource=s3)
+            # self.s3_resource might be None. If it is None, load_sagemaker_config will
+            # create a default S3 resource, but only if it needs to fetch from S3
+            self.sagemaker_config = load_sagemaker_config(s3_resource=self.s3_resource)
 
     @property
     def boto_region_name(self):

tests/integ/test_sagemaker_config.py

@@ -172,11 +172,20 @@ def test_config_download_from_s3_and_merge(
         sagemaker_session=sagemaker_session,
     )
 
+    # Set env variable so load_sagemaker_config can construct an S3 resource in the right region
+    previous_env_value = os.getenv("AWS_DEFAULT_REGION")
+    os.environ["AWS_DEFAULT_REGION"] = sagemaker_session.boto_session.region_name
+
     # The thing being tested.
     sagemaker_config = load_sagemaker_config(
         additional_config_paths=[s3_uri_config_1, config_file_2_local_path]
     )
 
+    # Reset the env variable to what it was before (if it was set before)
+    os.unsetenv("AWS_DEFAULT_REGION")
+    if previous_env_value is not None:
+        os.environ["AWS_DEFAULT_REGION"] = previous_env_value
+
     assert sagemaker_config == expected_merged_config