Change to use metacpan-base

Instead of using a base perl docker image, use the new metacpan-base
image and build the api upon that.

The result should be faster build times and smaller images. Environment
variables have been introduced for being able to switch the server that
is being executed in the image. Those variables are set in the `.env`
file.

Author: ssoriche

.env

@@ -0,0 +1,2 @@
+PGDB=db:5432
+API_SERVER=morbo -l http://*:5000 -w /metacpan-api --verbose

Dockerfile

@@ -1,18 +1,17 @@
-FROM perl:5.22
+FROM metacpan/metacpan-base:latest
 
 ENV PERL_MM_USE_DEFAULT=1 PERL_CARTON_PATH=/carton
 
-COPY wait-for-it.sh /
 COPY cpanfile cpanfile.snapshot /metacpan-api/
 WORKDIR /metacpan-api
 
-RUN apt-get update \
-    && apt-get install -y libgmp-dev rsync \
-    && cpanm App::cpm \
-    && cpm install -g Carton \
-    && useradd -m metacpan-api -g users \
+# CPM installations of dependencies does not install or run tests. This is
+# because the modules themselves have been tested, and the metacpan use of the
+# modules is tested by the test suite. Removing the tests, reduces the overall
+# size of the images.
+RUN useradd -m metacpan-api -g users \
     && mkdir /carton /CPAN \
-    && cpm install -L /carton \
+    && cpm install --without-test -L /carton \
     && rm -fr /root/.cpanm /root/.perl-cpm /var/cache/apt/lists/* /tmp/*
 
 RUN chown -R metacpan-api:users /metacpan-api /carton /CPAN
@@ -25,4 +24,4 @@ USER metacpan-api:users
 
 EXPOSE 5000
 
-CMD [ "/wait-for-it.sh", "db:5432", "--", "carton", "exec", "morbo", "-l", "http://*:5000", "-w", "root", "./bin/api.pl"]
+CMD /wait-for-it.sh ${PGDB} -- carton exec ${API_SERVER} ./bin/api.pl