php composer inside container lost vendor directory

Question

I have the following Dockerfile

FROM        bitgandtter/sf:php7

# basic env fix
ENV         TERM xterm

# install packages
ADD         .   /var/www

# update dependencies
RUN         cd Helpers && SYMFONY_ENV=prod composer update -o --no-dev

ENV         SYMFONY_ENV prod

After build the image the Helpers directory does not contain the vendor directory.

I really dont know why is that since the previous compsoer update just execute successfully and the image was created just fine.

Any help please

NOTE: the image bitgandtter/sf:php7 use a VOLUME declaration on /var/www

Answer 1

In fact i discover that the VOLUME declaration on the base image was the main issue.

As explained in the official doc after define a VOLUME on a dockerfile if any file changes happens inside that volume will be lost.

So the solution is to not declare VOLUMES on base images.