Building with Docker

Terminology

See Naming Conventions.

Overview

Docker is a container framework used to host a large collection of tools. Jenkins offers Docker integration so that tools can be used in a pipeline as if they were natively installed.

Creating a Step Using Docker

Docker containers are generally used on a per step basis. This is because typically we use the container to either build or test our application whilst still using the base JNLP image to create docker images or creating deployments.

To use a Docker image as part of the build process we use an agent block to define the container. This is done at the start of the stage block:

stage('Build Application'){
    agent{
        docker {
            image '${docker_image}'
            reuseNode true
        }
    }
    steps {
        echo 'Steps go here'
    }
}

The ${docker_image} is replaced by an image tag such as openjdk:11 if we wanted to build a JDK 11 application. All future steps in the stage are run in the context of the docker container. Note that reuseNode true MUST be set or all steps in this stage will be run in a different workspace.

Special Notes for Maven

When running Maven in Docker, to correctly use withMaven{} the path must be modified so that the extensions provided by withMaven are loaded correctly. This does not apply if the Maven wrapper (mvnw) is used.

stage('Build Project') {
    agent {
        docker {
            image 'maven:3-jdk-11'
            reuseNode true
        }
    }
    steps {
        withSonarQubeEnv('cessda-sonar') {
            withMaven {
                sh 'export PATH=$MVN_CMD_DIR:$PATH && mvn clean install'
            }
        }
    }
}