diff --git a/docs/chapter/enviromentvars.md b/docs/chapter/enviromentvars.md
new file mode 100644
index 00000000..f282ea36
--- /dev/null
+++ b/docs/chapter/enviromentvars.md
@@ -0,0 +1,40 @@
+# Environment Variables 
+
+There are couple of environment variables that GNES respect during runtime.
+
+## `GNES_PROFILING`
+
+Set to any non-empty string to turn on service-level time profiling for GNES.
+
+Default is disabled.
+
+## `GNES_PROFILING_MEM`
+
+Set to any non-empty string to turn on service-level memory profiling for GNES. Warning, memory profiling could hurt the efficiency significantly.
+
+Default is disabled.
+
+## `GNES_WARN_UNNAMED_COMPONENT`
+
+Set to `0` to turn off the warning like `this object is not named ("name" is not found under "gnes_config" in YAML config), i will call it "BaseRouter-51ce94cc". naming the object is important as it provides an unique identifier when serializing/deserializing this object.`
+
+Set to `1` to enable it. 
+
+Default is enabled.
+
+## `GNES_VCS_VERSION`
+
+Git version of GNES. This is used when `--check_version` is turned on. For GNES official docker image, `GNES_VCS_VERSION` is automatically set to the git version during the building procedure.
+
+Default is the git head version when building docker image. Otherwise it is not set.
+
+## `GNES_CONTROL_PORT`
+
+Control port of the microservice. Useful when doing health check via `gnes healthcheck`.
+
+Default is not set. A random port will be used.
+
+## `GNES_CONTRIB_MODULE`
+
+(*depreciated*) Paths of the third party components. See examples in GNES hub for latest usage.
+
diff --git a/docs/index.rst b/docs/index.rst
index 6436a644..1e8162ed 100644
--- a/docs/index.rst
+++ b/docs/index.rst
@@ -68,6 +68,7 @@ Highlights
 
    chapter/troubleshooting.md
    chapter/protobuf-dev.md
+   chapter/enviromentvars.md
 
 .. toctree::
    :maxdepth: 2
diff --git a/tests/test_healthcheck.py b/tests/test_healthcheck.py
index 9ecbe789..161d8d99 100644
--- a/tests/test_healthcheck.py
+++ b/tests/test_healthcheck.py
@@ -47,7 +47,7 @@ def test_health_check(self):
         self.assertEqual(cm.exception.code, 1)
 
     def test_hc_os_env(self):
-        os.environ.setdefault('GNES_CONTROL_PORT', str(56789))
+        os.environ['GNES_CONTROL_PORT'] = str(56789)
         a = set_router_parser().parse_args([
             '--yaml_path', 'BaseRouter',
         ])