deploying tornado on Google App Engine - google-app-engine

Question

I am trying to deploy my python pricing module which takes product details (string) as argument, on to GAE. The tornado wrapper is working fine on localhost (localhost:8888/?q=) but giving server error 500 on GAE.
Code in Pricing-OOP.py file:
class MainHandler(tornado.web.RequestHandler):
def get(self):
q = self.get_query_argument("q")
res = Pricing(q).pricing()
self.write(json.dumps(res))
def make_app():
return tornado.web.Application([
(r"/", MainHandler),
],debug=True)
if __name__ == '__main__':
Pickleload()
app = make_app()
container = tornado.wsgi.WSGIContainer(app)
http_server = tornado.httpserver.HTTPServer(container)
http_server.listen(8888)
tornado.ioloop.IOLoop.current().start()
app.yaml file:
service: tornado
runtime: python27
threadsafe: no
handlers:
- url: /.*
script: Pricing-OOP.py
The gcloud app logs tail is as follows:
2017-07-26 03:03:30 tornado[20170726t082447] "GET / HTTP/1.1" 500
2017-07-26 03:03:30 tornado[20170726t082447] "GET /favicon.ico HTTP/1.1" 500
2017-07-26 03:03:33 tornado[20170726t082447] "GET / HTTP/1.1" 500
2017-07-26 03:03:34 tornado[20170726t082447] "GET /favicon.ico HTTP/1.1" 500
How do I correct this?

Answer 1

There are a few notes regarding deploying on Google App Engine in the Tornado docs.
In particular, a Tornado application on GAE must be run as a WSGI application. You cannot do things like open ports on the local machine,
and unfortunately it also prevents the use of asynchronous aspects of Tornado (which are often the main driver for using it in the first place).
In your case, instead of creating the HttpServer yourself, you should just create the WSGIAdapter:
# Pricing-OOP.py
# ...
def make_app():
return tornado.web.Application([
(r"/", MainHandler),
],debug=False)
application = make_app()
application = tornado.wsgi.WSGIAdapter(application)
You then tell GAE where to find application by referencing it in the script directive of your configuration file:
# app.yaml
# ...
handlers:
- url: /.*
script: Pricing-OOP.application
Because you are now a "pure" WSGI application, you need to run it in a container. The Google Cloud SDK includes a development server in dev_appserver.py that can be used to host your app:
$ dev_appserver.py . # in directory containing app.yaml
That being done, you can run the same application code both locally and in your GAE instance.