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We can create a new container and define your application port in docker run command like

sudo docker run -d -p 5000:5000 training/webapp python app.py

or 

sudo docker run -d -P training/webapp python app.py

But, what if someone forgot to specify -p or -P option in docker run command? The container get created and runs the application locally. Now how could I assign a port on which application is running locally in container to the port of my Ubuntu host machine? Kindly, help on this. Thanks.

errordeveloper
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user3886523
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  • possible duplicate of [Exposing a port on a live Docker container](http://stackoverflow.com/questions/19897743/exposing-a-port-on-a-live-docker-container) – Hardy Sep 05 '14 at 13:03

1 Answers1

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Short: You can't. You need to stop the container (or not) and start a new one with the proper parameters.

Docker spins up a local proxy and setup the iptables for proper NAT. If you really can't start a new container, you could manually setup the iptables and spin up a socat. You can take a look at the network part of the Docker code for more info.

creack
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