Docker

We use the Docker runner for GitLab CI. This means it is no longer necessary to configure the build server or install software required for your build. Simply declare a [Docker] image in your .gitlab-ci.yml file.

Finding Docker Images

You can search on Docker Store for official images, or Docker Hub for community images.

Syntax for official images:

image: image:tag

Syntax for community images:

image: repo/image:tag

Missing Required Tooling

If the image you are using is missing some tooling your build requires, you can either find another image which contains the tools you need, or you can build a custom image. You can either create a completely custom image, or modify an existing Dockerfile and add the missing tools. In this case, you may test your image build using your personal projects, and then push the project to the DockerHelper namespace once the image builds and the image can build your project without issues.

The image tag for custom images is somewhat different from the official and community sources.

image: registry.felinewith.me/<namespace>/<project>:<git tag>

Example: .gitlab-ci.yml image: registry.felinewith.me/dockerhelper/maven:master

Custom Image Caveats

Our server will use the Docker-in-Docker image and tooling for building your custom/modified image. This means it will not work the same way as it would on your machine (if you have Docker installed locally) or on the server (via ssh). Additionally, the environment provided by the image you are modifying (with a modified Dockerfile) may use different package managers. Fortunately, several images are built using [Alpine Linux], so installing additional software from the apk repo is fairly easy, as in this example which installs Git:

apk update
apk get git

Example Custom Image

For this example, we will use registry.felinewith.me/dockerhelper/maven:master. The commands for installing curl, git, and bash can be seen added at line 10.

The reasons for this were:

Building the image requires curl.
Our maven builds require git.
The image requires bash for the entrypoint script to work correctly.

The default Docker template for .gitlab-ci.yml did not require modification.

Pristine

From https://github.com/carlossg/docker-maven/blob/ecf54b9839caed8aa2bcf9b8f7bb19594634ee89/jdk-8/Dockerfile

FROM openjdk:8-jdk

ARG MAVEN_VERSION=3.5.0
ARG USER_HOME_DIR="/root"
ARG SHA=beb91419245395bd69a4a6edad5ca3ec1a8b64e41457672dc687c173a495f034
ARG BASE_URL=https://apache.osuosl.org/maven/maven-3/${MAVEN_VERSION}/binaries

RUN mkdir -p /usr/share/maven /usr/share/maven/ref \
  && curl -fsSL -o /tmp/apache-maven.tar.gz ${BASE_URL}/apache-maven-$MAVEN_VERSION-bin.tar.gz \
  && echo "${SHA}  /tmp/apache-maven.tar.gz" | sha256sum -c - \
  && tar -xzf /tmp/apache-maven.tar.gz -C /usr/share/maven --strip-components=1 \
  && rm -f /tmp/apache-maven.tar.gz \
  && ln -s /usr/share/maven/bin/mvn /usr/bin/mvn

ENV MAVEN_HOME /usr/share/maven
ENV MAVEN_CONFIG "$USER_HOME_DIR/.m2"

COPY mvn-entrypoint.sh /usr/local/bin/mvn-entrypoint.sh
COPY settings-docker.xml /usr/share/maven/ref/

VOLUME "$USER_HOME_DIR/.m2"

ENTRYPOINT ["/usr/local/bin/mvn-entrypoint.sh"]
CMD ["mvn"]

Modified

From https://felinewith.me/DockerHelper/maven/blob/9fa955a4ad5ab129165e6529a4fa1312f965d8c6/Dockerfile

# This file is a template, and might need editing before it works on your project.
FROM openjdk:8-alpine

ARG MAVEN_VERSION=3.5.0
ARG USER_HOME_DIR="/root"
ARG SHA=beb91419245395bd69a4a6edad5ca3ec1a8b64e41457672dc687c173a495f034
ARG BASE_URL=https://apache.osuosl.org/maven/maven-3/${MAVEN_VERSION}/binaries

RUN mkdir -p /usr/share/maven /usr/share/maven/ref \
  && apk update && apk add curl && apk add git && apk add bash \
  && curl -fsSl -o /tmp/apache-maven.tar.gz ${BASE_URL}/apache-maven-$MAVEN_VERSION-bin.tar.gz \
  && echo "${SHA}  /tmp/apache-maven.tar.gz" | sha256sum -c - \
  && tar -xzf /tmp/apache-maven.tar.gz -C /usr/share/maven --strip-components=1 \
  && rm -f /tmp/apache-maven.tar.gz \
  && ln -s /usr/share/maven/bin/mvn /usr/bin/mvn

ENV MAVEN_HOME /usr/share/maven
ENV MAVEN_CONFIG "$USER_HOME_DIR/.m2"

COPY mvn-entrypoint.sh /usr/local/bin/mvn-entrypoint.sh
COPY settings-docker.xml /usr/share/maven/ref/

VOLUME "$USER_HOME_DIR/.m2"

ENTRYPOINT ["/usr/local/bin/mvn-entrypoint.sh"]
CMD ["mvn"]

Server Management