Mount directory in Container and share with Host

Mounting container directories to the host is against the docker concepts. That would break the process/resources encapsulation principle.

The other way around - mounting a host folder into a container - is possible. But I would rather suggest to use volume containers, instead.

After countless hours of research, I decided to extend my image with the following Dockerfile:

FROM sphinxsearch

VOLUME /usr/local/sphinx/etc
VOLUME /usr/local/sphinx/var

RUN mkdir -p /sphinx && cd /sphinx && cp -avr /usr/local/sphinx/etc . && cp -avr /usr/local/sphinx/var .

ADD docker-entrypoint.sh /
RUN chmod +x /docker-entrypoint.sh

ENTRYPOINT ["/docker-entrypoint.sh"]

Extending it benefited it me in that I didn't have to build the entire image from scratch as I was testing, and only building the parts that were relevant.

I created an ENTRYPOINT to execute a bash script that would copy the files back to the required destination for sphinx to run properly, here is that code:

#!/bin/sh
set -e

target=/usr/local/sphinx/etc

# check if directory exists
if [ -d "$target" ]; then
    # check if we have files
    if find "$target" -mindepth 1 -print -quit | grep -q .; then
        # no files don't do anything
        # we may use this if condition for something else later
        echo not empty, don\'t do anything...
    else
        # we don't have any files, let's copy the
        # files from etc and var to the right locations
        cp -avr /sphinx/etc/* /usr/local/sphinx/etc && cp -avr /sphinx/var/* /usr/local/sphinx/var
    fi
else
    # directory doesn't exist, we will have to do something here
    echo need to creates the directory...
fi

exec "$@"

Having access to the /etc & /var directories on the host allows me to adjust the files while keeping them preserved on the host in between restarts and so forth... I also have the data saved on the host which should survive the restarts.

I know it's a debated topic on data containers vs. storing on the host, at this moment I am leaning towards storing on the host, but will try the other method later. If anyone has any tips, advice, etc... to improve what I have or a better way, please share.

Thank you @h3nrik for suggestions and for offering help!