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Jenkins differences between tools and docker agent

Sorry it might be a simple question but what is the differences between using tools and docker agent.I think using docker agent is much more flexible instead of using tools. When should I use docker agent or tools?

Tools

pipeline {
    agent any
    tools {
        maven 'Maven 3.3.9'
        jdk 'jdk8'
    }
    stages {
        stage ('Initialize') {
            steps {
                sh '''
                    echo "PATH = ${PATH}"
                    echo "M2_HOME = ${M2_HOME}"
                '''
            }
        }

        stage ('Build') {
            steps {
                sh 'mvn -Dmaven.test.failure.ignore=true install' 
            }

Docker Agent

pipeline {
agent none
stages {
    stage('Back-end') {
        agent {
            docker { image 'maven:3-alpine' }
        }
        steps {
            sh 'mvn --version'
        }
    }
Solution

  • These two options serve a bit different purpose. The tools block allows you to add specific versions of maven, jdk, or gradle in your PATH. You can't use any version - you can only use versions that are configured in the Global Tool Configuration Jenkins page:

    enter image description here

    If your Jenkins configuration contains only a single Maven version, e.g., Maven 3.6.3, you can use only this version. Specifying a version that is not configured in the Global Tool Configuration will cause your pipeline to fail.

    pipeline {
    agent any
    tools {
        maven 'Maven 3.6.3' 
    }
    stages {
        stage('Example') {
            steps {
                sh 'mvn --version'
            }
        }
    }
}

    Using the tools block to specify different versions of supported tools will be a good option if your Jenkins server does not support running docker containers.

    The docker agent, on the other hand, gives you total freedom when it comes to specifying tools and their versions. It does not limit you to maven, jdk, and gradle, and it does not require any pre-configuration in your Jenkins server. The only tool you need is docker, and you are free to use any tool you need in your Jenkins pipeline.

    pipeline {
    agent {
        docker {
            image "maven:3.6.3-jdk-11-slim"
        }
    }
    stages {
        stage('Example') {
            steps {
                sh 'mvn --version'
            }
        }
    }
}

    When to use one over another?

    There is no single right answer to this question. It depends on the context. The tools block is very limiting, but it gives you control over what tools are used in your Jenkins. In some cases, people decide not to use docker in their Jenkins environment, and they prefer to control what tools are available to their users. We can agree with this or not. When it comes to using the docker agent, you get full access to any tools that can be shipped as a docker container. In some cases, this is the best choice when it comes to using a tool with a specific version - your operating system may not allow you to install the desired version. Of course, you need to keep in mind that this power and flexibility comes with a cost. You lose control over what tools are used in your Jenkins pipelines. Also, if you pull tons of different docker images, you will increase disk space consumption. Not to mention that the docker agent allows you to run the pipeline with tools that may consume lots of CPU and memory. (I have seen Jenkins pipelines starting Elasticsearch, Logstash, Zookeeper, and other services, on nodes that were not prepared for that load.)