Adds DASH and PORT env vars to run_server

Author: OwenMatsuda

CHANGELOG.md

@@ -3,6 +3,9 @@ All notable changes to `dash` will be documented in this file.
 This project adheres to [Semantic Versioning](http://semver.org/).
 
 ## [Unreleased]
+### Added
+- [#1134](https://github.com/plotly/dash/pull/1134) Allow `dash.run_server()` host and port parameters to be set with environment variables HOST & PORT, respectively
+
 ### Changed
 - [#1145](https://github.com/plotly/dash/pull/1145) Update from React 16.8.6 to 16.13.0
 

dash/dash.py

@@ -1841,7 +1841,8 @@ def delete_resource(resources):
 
     def run_server(
         self,
-        port=8050,
+        host=os.getenv("HOST", "127.0.0.1"),
+        port=os.getenv("PORT", "8050"),
         debug=False,
         dev_tools_ui=None,
         dev_tools_props_check=None,
@@ -1860,7 +1861,12 @@ def run_server(
         If a parameter can be set by an environment variable, that is listed
         too. Values provided here take precedence over environment variables.
 
+        :param host: Host IP used to serve the application
+            env: ``HOST``
+        :type host: string
+
         :param port: Port used to serve the application
+            env: ``PORT``
         :type port: int
 
         :param debug: Set Flask debug mode and enable dev tools.
@@ -1933,9 +1939,18 @@ def run_server(
             dev_tools_prune_errors,
         )
 
+        # Verify port value
+        try:
+            port = int(port)
+            assert port in range(1, 65536)
+        except Exception as e:
+            e.args = [
+                "Expecting an integer from 1 to 65535, found port={}".format(repr(port))
+            ]
+            raise
+
         if self._dev_tools.silence_routes_logging:
             # Since it's silenced, the address doesn't show anymore.
-            host = flask_run_options.get("host", "127.0.0.1")
             ssl_context = flask_run_options.get("ssl_context")
             self.logger.info(
                 "Running on %s://%s:%s%s",
@@ -1955,4 +1970,4 @@ def run_server(
 
             self.logger.info("Debugger PIN: %s", debugger_pin)
 
-        self.server.run(port=port, debug=debug, **flask_run_options)
+        self.server.run(host=host, port=port, debug=debug, **flask_run_options)