python - Docker input file and save in output

Question

I built a docker image that inputs a local file, does some stuff to it, and returns an output file saved locally, but it does not work. How do I allow local, user input for files and then saving the output on the local machine?

My Dockerfile looks like this:

FROM python:3
WORKDIR /app
COPY requirements.txt .
RUN pip install -r requirements.txt
COPY . /app
EXPOSE 5000
CMD [ "python", "process.py" ]

Ideally, the terminal command would be something like this:

docker run -p 5000:5000 [name of docker] [local path to input file] [local path to save output file]

When I run, I get this error:

docker: Error response from daemon: OCI runtime create failed: container_linux.go:349: starting container process caused "exec: "../test.flac": stat ../test.flac: no such file or directory": unknown.

How can I do this?

Answer 1

Generally, the docker container cannot break out into the host machine.

However, you can mount a local directory from the host machine into the container. The files created in the mount point, inside the container, will also be visible on the host machine.

In the example below I am mounting the working directory from the host machine inside the container. My current directory contains an input-file.
The container cat_s the content of the input-file and appends it to the output-file

// The initial wiorking directory content
.
└── input-file

// Run my dummy container and ask it to cat the content of the input file into the output file
docker run -v $(pwd):/root/some-path ubuntu /bin/bash -c "cat /root/some-path/input-file >> /root/some-path/output-file"

// The outcome
.
├── input-file
└── output-file