unable to run more than one tornado process

Question

I've developed a tornado app but when more than one user logs in it seems to log the previous user out. I come from an Apache background so I thought tornado would either spawn a thread or fork a process but seems like that is not what is happening.

To mitigate this I've installed nginx and configured it as a reverse proxy to forward incoming requests to an available tornado process. Nginx seems to work fine however when I try to start more than one tornado process using a different port I get the following error:

http_server.listen(options.port)
File "/usr/local/lib/python2.7/dist-packages/tornado/tcpserver.py", line 125, in listen
sockets = bind_sockets(port, address=address)
File "/usr/local/lib/python2.7/dist-packages/tornado/netutil.py", line 145, in bind_sockets
sock.bind(sockaddr)
File "/usr/lib/python2.7/socket.py", line 224, in meth
return getattr(self._sock,name)(*args)
socket.error: [Errno 98] Address already in use

basically i get this for each process I try to start on a different port.

I've read that I should use supervisor to manage my tornado processes but I'm thinking that is more of a convenience. At the moment I'm wondering if the problem has to do with my actual tornado code or my setup somewhere? My python code looks like this:

from tornado.options import define, options
define("port", default=8000, help="run on given port", type=int)
....
http_server = tornado.httpserver.HTTPServer(app)
http_server.listen(options.port)
tornado.ioloop.IOLoop.instance().start()

my handlers all work fine and I can access the site when I go to localhost:8000 just need a pair of fresh eyes please. ;)

Answer 1

Well I solved the problem. I had .sh file that tried to start multiple processes with:

python initpumpkin.py --port=8000&
python initpumpkin.py --port=8001&
python initpumpkin.py --port=8002&
python initpumpkin.py --port=8003&

unfortunately I didn't tell tornado to parse the command line options so I would always get that address always in use error since port '8000' was defined as my default port, so it would attempt to listen on that port each time. In order to mitigate this make sure to declare tornado.options.parse_command_line() after main:

if __name__ == "__main__":
    tornado.options.parse_command_line()

then run from the CLI with whatever arguments.

Answer 2

Have you tried starting your server in this manner:

server = tornado.httpserver.HTTPServer(app)
server.bind(port, "0.0.0.0")
server.start(0)

IOLoop.current().start()

server.start takes a parameter for number of processes where 0 tells Tornado to use one process per CPU on the machine