Merge pull request #1344 from neilinger/docker_improvements

Docker improvements

src/DockerBase/Dockerfile

@@ -2,9 +2,22 @@ FROM ubuntu:16.04
 
 MAINTAINER GitTools Maintainers <[email protected]>
 
-# Wheezy doesn't support glibc 2.15 which libgit2sharp requires
-# So we are going to install mono on ubuntu instead
-RUN apt-key adv --keyserver hkp://keyserver.ubuntu.com:80 --recv-keys 3FA7E0328081BFF6A14DA29AA6A19B38D3D831EF
-RUN echo "deb http://download.mono-project.com/repo/debian wheezy main" | tee /etc/apt/sources.list.d/mono-xamarin.list
-RUN apt-get update && apt-get install libcurl3 tzdata unzip curl git-all mono-complete -y && apt-get -yqq clean
-RUN cp /usr/share/zoneinfo/GMT /etc/localtime
+# moviong the timezone setting at the top, as this may be the most infrequent change in this file
+RUN ln -sfn /usr/share/zoneinfo/GMT /etc/localtime
+
+# Following current install guide from
+# http://www.mono-project.com/download/#download-lin on 2017-12-08
+# regarding to the repository sources
+RUN echo "deb http://download.mono-project.com/repo/ubuntu xenial main" |\
+    tee /etc/apt/sources.list.d/mono-official.list
+
+# This will do:
+# * Accept the repository key
+# * Get the current package inventory state
+# * Install given packages only with required dependencies
+# * Cleanup to reduce Docker image size
+RUN apt-key adv --keyserver hkp://keyserver.ubuntu.com:80 --recv-keys 3FA7E0328081BFF6A14DA29AA6A19B38D3D831EF &&\
+    apt-get update &&\
+    apt-get  -y --no-install-recommends install libcurl3 tzdata unzip curl git-all mono-complete &&\
+    apt-get -yqq clean &&\
+    rm -rf /var/lib/apt/lists/* /tmp/*