Unable to Connect to Flask App On Docker From Host [duplicate]

Question

I've setup a docker ubuntu 14.04 image and I'm running it with the following command:

docker run -d -p 5000:5000 ari/python3-flask

The Dockerfile:

FROM ubuntu:14.04
RUN apt-get update && apt-get install -y python3 python3-pip
ADD . /var/my_app
RUN pip3 install -r /var/my_app/requirements.txt
EXPOSE 5000
CMD ["python3", "/var/my_app/runserver.py"]

However, if I attempt to curl the address (localhost:5000) or visit it in a browser I get a connection failed error.

The docker log for the container shows:

Running on http://127.0.0.1:5000/

Restarting with reloader

Does anyone what is or could be wrong with my docker setup and/or configuration? Thanks.

Answer 1

The web server running in your container is listening for connections on port 5000 of the loopback network interface (127.0.0.1). As such this web server will only respond to http requests originating from that container itself.

In order for the web server to accept connections originating from outside of the container you need to have it bind to the 0.0.0.0 IP address.

As you are using Flask, this can be easily achieved in your runserver.py file by using:

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

Then when you start your container and look at the log, you should see something like:

 * Running on http://0.0.0.0:5000/