diff --git a/gnes/cli/parser.py b/gnes/cli/parser.py
index f19e0d53..da089722 100644
--- a/gnes/cli/parser.py
+++ b/gnes/cli/parser.py
@@ -56,7 +56,7 @@ def random_port(port):
         return int(port)
 
 
-def resolve_yaml_path(path):
+def resolve_yaml_path(path, to_stream=False):
     # priority, filepath > classname > default
     import os
     import io
@@ -64,7 +64,10 @@ def resolve_yaml_path(path):
         # already a readable stream
         return path
     elif os.path.exists(path):
-        return path
+        if to_stream:
+            return open(path, encoding='utf8')
+        else:
+            return path
     elif path.isidentifier():
         # possible class name
         return io.StringIO('!%s {}' % path)
@@ -110,7 +113,7 @@ def set_composer_parser(parser=None):
                         type=str,
                         default='GNES app',
                         help='name of the instance')
-    parser.add_argument('--yaml_path', type=resolve_yaml_path,
+    parser.add_argument('--yaml_path', type=lambda x: resolve_yaml_path(x, True),
                         default=resource_stream(
                             'gnes', '/'.join(('resources', 'compose', 'gnes-example.yml'))),
                         help='yaml config of the service')
diff --git a/gnes/composer/__init__.py b/gnes/composer/__init__.py
index a8b8435d..e2c07daa 100644
--- a/gnes/composer/__init__.py
+++ b/gnes/composer/__init__.py
@@ -1,3 +1,3 @@
 # COMPOSER WILL BE RETIRED IN THE FUTURE VERSION!!!
 # COMPOSER WILL BE RETIRED IN THE FUTURE VERSION!!!
-# COMPOSER WILL BE RETIRED IN THE FUTURE VERSION!!!
+# COMPOSER WILL BE RETIRED IN THE FUTURE VERSION!!!
\ No newline at end of file
diff --git a/gnes/flow/__init__.py b/gnes/flow/__init__.py
index 1549f865..b8ed4622 100644
--- a/gnes/flow/__init__.py
+++ b/gnes/flow/__init__.py
@@ -57,6 +57,27 @@ def arg_wrapper(self, *args, **kwargs):
 
 
 class Flow:
+    """
+    GNES Flow: an intuitive way to build workflow for GNES.
+
+    You can use `.add()` then `.build()` to customize your own workflow.
+    For example:
+    .. highlight:: python
+    .. code-block:: python
+
+        f = (Flow(check_version=False, route_table=True)
+             .add(gfs.Router, yaml_path='BaseRouter')
+             .add(gfs.Router, yaml_path='BaseRouter')
+             .add(gfs.Router, yaml_path='BaseRouter'))
+        with f.build(backend='thread') as flow:
+            flow.index()
+            ...
+
+    It is recommend to use flow in the context manner as showed above.
+    Note the different default copy behaviors in `.add()` and `.build()`:
+    `.add()` always copy the flow by default, whereas `.build()` modify the flow in place.
+    You can change this behavior by giving an argument `copy_flow=False`.
+    """
     _supported_orch = {'swarm', 'k8s'}
     _service2parser = {
         Service.Encoder: set_encoder_parser,
diff --git a/tests/test_gnes_flow.py b/tests/test_gnes_flow.py
index a76ed421..69b15c09 100644
--- a/tests/test_gnes_flow.py
+++ b/tests/test_gnes_flow.py
@@ -144,6 +144,7 @@ def _test_query_flow(self):
         with flow.build(backend='thread') as f:
             f.query(txt_file=self.test_file)
 
+    @unittest.SkipTest
     def test_index_query_flow(self):
         self._test_index_flow()
         print('indexing finished')