Problems building an Ubuntu docker container for a distribution - docker

Question

I'm trying to build a Docker container for this module. Main idea is that I'm trying to use, as much as possible, the packages provided by Ubuntu to avoid problem; I'm also using the default perl that comes with the container, which apparently is 5.22.
This is the Dockerfile:
FROM ubuntu:16.04
LABEL version="1.0" maintainer="JJ Merelo <jjmerelo#GMail.com>" perl5version="5.22"
ADD data/* ./
ADD . .
RUN mkdir /test \
&& apt-get update \
&& apt-get install -y build-essential curl hunspell-en-us libtext-hunspell-perl myspell-es libencode-perl cpanminus libfile-slurp-tiny-perl libversion-perl\
&& curl https://raw.githubusercontent.com/SublimeText/Dictionaries/master/Spanish.dic -o Spanish.dic
RUN cpanm .
RUN perl --version
VOLUME /test
WORKDIR /test
# Will run this
ENTRYPOINT prove
It builds locally without a problem (using Docker version 17.05.0-ce, build 89658be). However, it does not work in Docker hub due to this problem
/etc/ssl/certs/AddTrust_Low-Value_Services_Root.pem is encountered a second time at /usr/share/perl/5.22/File/Find.pm line 79.
Which seems to happen in a line where I do perl Makefile.PL && make install
I really have no idea what could be the cause for that, of why it works locally and fails there. Any idea?

Answer 1

I think the problem is that you do WORKDIR /test too late. In the beginning of Dockerfile you do ADD . . this will copy all files from the current directory of your local filesystem to the root directory of the image. The problem is that there can be conflicts between the directories already present in the root of the image, like /lib. Try instead something like this:
FROM ubuntu:16.04
LABEL version="1.0" maintainer="JJ Merelo <jjmerelo#GMail.com>" perl5version="5.22"
WORKDIR /test
ADD data/* ./
ADD . .
RUN apt-get update \
&& apt-get install -y build-essential curl hunspell-en-us libtext-hunspell-perl myspell-es libencode-perl cpanminus libfile-slurp-tiny-perl libversion-perl\
&& curl https://raw.githubusercontent.com/SublimeText/Dictionaries/master/Spanish.dic -o Spanish.dic
RUN perl --version
RUN cpanm Test::More
RUN cpanm .
VOLUME /test
# Will run this
ENTRYPOINT prove

Answer 2

The problem is that we don't use a working directory for copying the files we want to have included in the directory, and then we do ADD . .. That includes a lib directory, so we are then copying the contents of our module to the lib directory, that is, the image /lib directory.
That's not bad per se. The problem is that the Perl installation procedure is then copying the contents of its own lib directory (which is the system's lib directory) onto blib, and then again, copyint that to some directory of /usr/lib. Somehow there's installation happening in other directories, which means that that certificate mentioned in the error is eventually copied somewhere else, hence the duplicate.
That does not explain why it was working locally, and as a matter of fact working in subsequent builds in Docker Hub. Maybe some slightly different version of runc. But even if it works, you end up with stuff duplicated, and a bigger image than you should have.
Baseline is: don't use root as working directory. Use WORKDIR from the very beginning, even more so if that directory is going to have stuff that's going to be installed somewhere else.