Docker python OSError 98 Address already in use

Question

I have python application which uses Flask for accepting REST requests (on port 5000) and Tornado for accepting websocket connections (on port 8888). I want to run the application on Windows machine.

The application runs fine when I run it using python -m flask run

Now, I want to dockerize the application.

My Dockerfile is:

FROM python:3.8.3
COPY ./requirements.txt /app/requirements.txt
WORKDIR /app
RUN pip install -r requirements.txt
COPY . /app
CMD ["python","app.py"]

My requirements.txt is:

autobahn==20.6.2
cryptography==2.9.2
ecdsa==0.15
Flask==1.1.2
PyJWT==1.7.1
requests==2.24.0
tornado==6.0.4
Twisted==20.3.0
urllib3==1.25.9
websocket-client==0.57.0
websockets==8.1

app.py:

from flask import Flask, request, Response, make_response

app = Flask(__name__)

init_ws_server_thread()
 
@app.route("/")
def home():
    return "Hello, Flask!"

def init_ws_server_thread():
    print('init server thread')
    try:            
        t = Thread(target=initialize_websocket_server, args=())
        t.start()
    except Exception as e:
        print('init_ws_server_thread Exception:', e)

def initialize_websocket_server():
    print('initialize_websocket_server')

    asyncio.set_event_loop(asyncio.new_event_loop())

    app = make_app()
    app.listen(8888)
    tornado.ioloop.IOLoop.current().start()

def make_app():
    return tornado.web.Application([
        (r"/", MainHandler),
    ])

class MainHandler(tornado.websocket.WebSocketHandler):
    def open(self):
        global g_ws
        print("New client connected", self.request.remote_ip)
        g_ws = self
        self.write_message("You are connected")

    def on_message(self, message):
        self.write_message(u"You said: " + message)

    def on_close(self):
        print("Client disconnected")

    def check_origin(self, origin):
        return True


if __name__ == '__main__':
    app.run(debug = True, host = '0.0.0.0')

Docker commands:

docker build -t my-app:0.0.0.1 .
docker run -d -p 5000:5000 my-app:0.0.0.1

When the docker image is run, the REST requests are being served by Flask (http://localhost:5000) But I get the following exception for websocket:

Exception in thread Thread-1:

Traceback (most recent call last):    
File "/usr/local/lib/python3.8/threading.py", line 932, in _bootstrap_inner
self.run()    
File "/usr/local/lib/python3.8/threading.py", line 870, in run    
self._target(*self._args, **self._kwargs)    
File "/app/websocket_server.py", line 57, in initialize_websocket_server    
app.listen(8888)    
File "/usr/local/lib/python3.8/site-packages/tornado/web.py", line 2116, in listen    
server.listen(port, address)    
File "/usr/local/lib/python3.8/site-packages/tornado/tcpserver.py", line 151, in listen    
sockets = bind_sockets(port, address=address)    
File "/usr/local/lib/python3.8/site-packages/tornado/netutil.py", line 174, in bind_sockets    
sock.bind(sockaddr)    
OSError: [Errno 98] Address already in use

I tried to expose port 8888 using EXPOSE 8888 or by doing docker run -d -p 5000:5000 -p 8888:8888 my-app:0.0.0.1, but not working

What could be going wrong?

Docker python OSError 98 Address already in use

0 Answers