[ci] Update Dockerfile to use Ubuntu 18.04 instead of 16.04

Also add parameter to pick specific versions of Ubuntu.

tools/ci-scripts/linux/image-builder/Dockerfile

@@ -1,4 +1,7 @@
-FROM ubuntu:16.04
+ARG UBUNTU_VERSION=18.04
+FROM ubuntu:$UBUNTU_VERSION
+# https://docs.docker.com/engine/reference/builder/#understand-how-arg-and-from-interact
+ARG UBUNTU_VERSION
 
 # Cache folders
 VOLUME /root/.ccache /root/.stack
@@ -34,19 +37,6 @@ RUN apt-get -y install \
     clang \
     cmake
 
-# Components for Haskell. See https://docs.haskellstack.org/en/stable/install_and_upgrade/#linux
-RUN wget -qO- https://get.haskellstack.org/ | sh
-
-# Components for C#. See http://www.mono-project.com/download/#download-lin
-RUN apt-key adv --keyserver hkp://keyserver.ubuntu.com:80 --recv-keys 3FA7E0328081BFF6A14DA29AA6A19B38D3D831EF && \
-    echo "deb https://download.mono-project.com/repo/ubuntu xenial main" | tee /etc/apt/sources.list.d/mono-official.list && \
-    apt-get update && \
-    apt-get -y install \
-    mono-devel \
-    nuget \
-    referenceassemblies-pcl
-RUN nuget install NUnit.ConsoleRunner -OutputDirectory /root -Version 3.8.0 -NonInteractive -ExcludeVersion
-
 # Components for Java
 RUN add-apt-repository ppa:cwchien/gradle && \
     apt-get update && \
@@ -54,6 +44,9 @@ RUN add-apt-repository ppa:cwchien/gradle && \
     gradle-6.8.3 \
     openjdk-8-jdk-headless
 
+# Components for Haskell. See https://docs.haskellstack.org/en/stable/install_and_upgrade/#linux
+RUN wget -qO- https://get.haskellstack.org/ | sh
+
 # Components for ghc
 RUN add-apt-repository ppa:hvr/ghc -y && \
     apt-get update && \
@@ -64,5 +57,23 @@ RUN add-apt-repository ppa:git-core/ppa -y && \
     apt-get update && \
     apt-get install --no-install-recommends git -y
 
+
+# we need to set bash to be able to use if statement
+SHELL ["/bin/bash", "-c"]
+
+# Components for C#. See http://www.mono-project.com/download/#download-lin
+RUN if [ "$UBUNTU_VERSION" = "18.04" ] || [ "$UBUNTU_VERSION" = "20.04" ] ; then apt install gnupg ca-certificates; fi
+
+RUN apt-key adv --keyserver hkp://keyserver.ubuntu.com:80 --recv-keys 3FA7E0328081BFF6A14DA29AA6A19B38D3D831EF
+
+RUN if [[ "$UBUNTU_VERSION" = "16.04" ]] ; then echo "deb https://download.mono-project.com/repo/ubuntu stable-xenial main"; \
+    elif [[ "$UBUNTU_VERSION" = "18.04" ]] ; then echo "deb https://download.mono-project.com/repo/ubuntu stable-bionic main"; \
+    elif [[ "$UBUNTU_VERSION" = "20.04" ]] ; then echo "deb https://download.mono-project.com/repo/ubuntu stable-focal main"; fi \
+    | tee /etc/apt/sources.list.d/mono-official.list && apt-get update && apt-get -y install \
+    mono-devel \
+    nuget \
+    referenceassemblies-pcl
+RUN nuget install NUnit.ConsoleRunner -OutputDirectory /root -Version 3.8.0 -NonInteractive -ExcludeVersion
+
 # Build script
 ENTRYPOINT ["zsh", "/root/bond/tools/ci-scripts/linux/build.zsh"]

tools/ci-scripts/linux/image-builder/README.md

@@ -3,7 +3,7 @@
 This directory contains the source for a Docker image that is used for
 building Bond.
 
-The image is based on Ubuntu 16.04 (Xenial Xerus) and contains:
+The image is based on Ubuntu 18.04 (Bionic Beaver) and contains:
 
 * pre-installed build tools for the various languages Bond supports,
 * binaries of a number of Boost versions for the C++ and Python builds, and
@@ -15,7 +15,7 @@ The image is based on Ubuntu 16.04 (Xenial Xerus) and contains:
 
 A new image is automatically built when the master branch of the main Bond
 repository (https://github.com/microsoft/bond) is changed. These images are
-then pushed to the bondciimages.azurecr.io/ubuntu-1604 container repository.
+then pushed to the bondciimages.azurecr.io/ubuntu-1804 (also bondciimages.azurecr.io/ubuntu-1604) container repository.
 The Travis CI builds pull a fixed version of the image specified in
 `.travis.yml` and use that.
 
@@ -56,7 +56,7 @@ zsh is only needed to debug and work on `build_boost.zsh` locally.
 
 To create the image, start in the directory containing this README and run:
 
-    $ docker build -t bond-ubuntu-1604 .
+    $ docker build --no-cache -t bond-ubuntu-1804 --build-arg UBUNTU_VERSION="18.04"
 
 This will make the Docker image with all the required dependencies and will
 compile all the required versions of Boost (using the `build_boosts.zsh`
@@ -64,7 +64,7 @@ script) that will become part of the image.
 
 The build takes about 20 minutes on a quad-core 3.3 GHz Skylake Xeon. When
 it finishes, there will be a new Docker image with the tag
-`bond-ubuntu-1604` in your collection of Docker images:
+`bond-ubuntu-1804` in your collection of Docker images:
 
     $ docker images
 
@@ -74,7 +74,7 @@ You can build Bond inside the container:
 
     $ docker run \
         -v path/to/your/bond/repository:/root/bond \
-        bond-ubuntu-1604 \
+        bond-ubuntu-1804 \
         ~ \
         cpp-core \
         1.64.0 \