docker container port forwarding behavior for `run` command (for websockets)

Question

I am running an ipython notebook server inside a docker container. Running code inside the notebook from the browser works over websockets, which have to connect from outside the container (a browser) to the tornado server running inside.

I noticed that when I start the notebook server directly with a docker run command

$ docker run -p 9000:9000 username/image ipython notebook --port=9000 --ip="*" 

I cannot get a connection (the ipython notebook kernel connection times out). When I start a shell in the docker container with and the run the same command inside the container, the connection works perfectly:

$ docker run -it -p 9000:9000 username/image /bin/bash $ ipython notebook --port=9000 --ip="*" # inside docker image 

In both cases, the ipython server log contains entries like

Connecting to: tcp://127.0.0.1:39946 

for the websocket connections.

This makes it harder to script and autorun the container. What can I do to get the same behavior as in the second case direclty from running the image?

Answer 1

Seems your ipython command requires to be run in bash - you should check the ENTRYPOINT of your Dockerfile, running ipython directly is not working for you.

Pass /bin/bash to the docker run command as so to test:

docker run -p 9000:9000 username/image /bin/bash -c 'ipython notebook --port=9000 --ip="*"'