Unable to access local docker container with IP address

Question

I am running a docker container locally on my Mac system. I have pasted the Dockerfile contents at the bottom of this post. I have exposed port 8888 in the image and I would like to access the python program from my host browser using container-ip-address:8888. But, it doesn't connect. Mapping it to a port on localhost works, but I don't want to do that. How can I solve this? (Already tried creating a docker network and running the container as part of the new network - no dice). Any help would be much appreciated. Dockerfile contents -

FROM python:latest

RUN mkdir -p /usr/src/app
WORKDIR /usr/src/app

COPY . /usr/src/app

EXPOSE 8888
RUN pip install tornado
CMD ["python", "./api.py" ]

Answer 1

Expose just tells docker that this container going to work with this port. it doesn't map it anywhere. https://docs.docker.com/engine/reference/builder/#expose

Mapping is the task of code which is running your container. In case of local machine its a docker. If you don't map port in docker run then container will not be accessible from outside of docker network. At the same time your host machine is not in docker network. Same in case if you create docker network manually - your machine just doesn't have access to inner parts of it.

In other words you have to choose your way:

• use -p .... when you do docker run (local development)
• or define it in docker compose file if you use docker composer (mostly local development). this approach is very useful when you are running multiple communicating systems in docker.
• or do it through kubernetes yaml definition file on production if you go into kubernetes with your solution (production with orchestrator/ autoscaler and etc.)