Python Environment: add gevent based WSGI server framework (#750)

* Python Environment: add gevent based WSGI server framework

This supply gevent based WSGI server framework to Python Environment, to
allow customer to run their functions under multi-threads.

* classify the flask based application

This set up the flask based application as individual class, to make
sure the consistent and integrity.

* Add instruction of WSGI server selection applied in Python Environment

* Python Environment starting logger: provide framework name

environments/python/README.md

@@ -43,3 +43,23 @@ Or, if you already have an environment, you can update its image:
 
 After this, fission functions that have the env parameter set to the
 same environment name as this command will use this environment.
+
+## Web Server Framework
+
+Python environment build and start a WSGI server, to support high HTTP 
+traffic. As it is applied in different use cases, this provides two server
+frameworks: `bjoern` and `gevent`. They all support high concurrency request.
+
+`bjoern` has good performance on RPS, to be ideal for most light resource 
+utilization cases.
+
+`gevent` is a good supplement because of its internal multi-threads. It 
+supports heavy resource load functions, with well distribution of response 
+time.
+
+Python environment pod remains `bjoern` framework by default. And it runs `gevent` 
+framework by setting the container environment `WSGI_FRAMEWORK` value to `GEVENT`. 
+
+The environment value is configured normally in two ways. One way is to set in Dockerfile 
+and build it into image. The other way is to set in Kubernetes deployment spec during 
+pod running and restart it.

environments/python/requirements.txt

@@ -5,3 +5,4 @@ python-dateutil
 requests==2.7.0
 redis
 hiredis
+gevent

environments/python/server.py

@@ -5,24 +5,40 @@ import sys
 import imp
 import os
 import bjoern
-
+from gevent.pywsgi import WSGIServer
 from flask import Flask, request, abort, g
 
-app = Flask(__name__)
+class FuncApp(Flask):
+    def __init__(self, name, loglevel = logging.DEBUG):
+        super(FuncApp, self).__init__(name)
 
-userfunc = None
+        # init the class members
+        self.userfunc = None
+        self.root = logging.getLogger()
+        self.ch = logging.StreamHandler(sys.stdout)
 
-@app.route('/specialize', methods=['POST'])
+        #
+        # Logging setup.  TODO: Loglevel hard-coded for now. We could allow
+        # functions/routes to override this somehow; or we could create
+        # separate dev vs. prod environments.
+        #
+        self.root.setLevel(loglevel)
+        self.ch.setLevel(loglevel)
+        self.ch.setFormatter(logging.Formatter('%(asctime)s - %(levelname)s - %(message)s'))
+        self.logger.addHandler(self.ch)
+
+        #
+        # Register the routers
+        #
+        @self.route('/specialize', methods=['POST'])
         def load():
-    global userfunc
             # load user function from codepath
             codepath = '/userfunc/user'
-    userfunc = (imp.load_source('user', codepath)).main
+            self.userfunc = (imp.load_source('user', codepath)).main
             return ""
 
-@app.route('/v2/specialize', methods=['POST'])
+        @self.route('/v2/specialize', methods=['POST'])
         def loadv2():
-    global userfunc
             body = request.get_json()
             filepath = body['filepath']
             handler = body['functionName']
@@ -58,17 +74,17 @@ def loadv2():
                 mod = imp.load_source(moduleName, filepath)
         
             # load user function from module
-    userfunc = getattr(mod, funcName)
+            self.userfunc = getattr(mod, funcName)
         
             return ""
 
-@app.route('/healthz', methods=['GET'])
+        @self.route('/healthz', methods=['GET'])
         def healthz():
             return "", 200
 
-@app.route('/', methods=['GET', 'POST', 'PUT', 'HEAD', 'OPTIONS', 'DELETE'])
+        @self.route('/', methods=['GET', 'POST', 'PUT', 'HEAD', 'OPTIONS', 'DELETE'])
         def f():
-    if userfunc == None:
+            if self.userfunc == None:
                 print("Generic container: no requests supported")
                 abort(500)
             #
@@ -78,26 +94,18 @@ def f():
             #   g.myKey = myValue
             # And the user func can then access that (after doing a "from flask import g").
             #
-    return userfunc()
+            return self.userfunc()
 
-#
+app = FuncApp(__name__, logging.DEBUG)
-# Logging setup.  TODO: Loglevel hard-coded for now. We could allow
-# functions/routes to override this somehow; or we could create
-# separate dev vs. prod environments.
-#
-def setup_logger(loglevel):
-    global app
-    root = logging.getLogger()
-    root.setLevel(loglevel)
-    ch = logging.StreamHandler(sys.stdout)
-    ch.setLevel(loglevel)
-    ch.setFormatter(logging.Formatter('%(asctime)s - %(levelname)s - %(message)s'))
-    app.logger.addHandler(ch)
 
 #
 # TODO: this starts the built-in server, which isn't the most
 # efficient.  We should use something better.
 #
-setup_logger(logging.DEBUG)
+if os.environ.get("WSGI_FRAMEWORK") == "GEVENT":
-app.logger.info("Starting server")
+    app.logger.info("Starting gevent based server")
+    svc = WSGIServer(('0.0.0.0', 8888), app)
+    svc.serve_forever()
+else:
+    app.logger.info("Starting bjoern based server")
     bjoern.run(app, '0.0.0.0', 8888, reuse_port=True)