Creating a Jenkinsfile

A Jenkinsfile is a text file that contains the definition of a Jenkins Pipeline and is checked into source control. Consider the following Pipeline which implements a basic three-stage continuous delivery pipeline.

// Declarative //
pipeline {
    agent any

    stages {
        stage('Build') {
            steps {
                echo 'Building..'
            }
        }
        stage('Test') {
            steps {
                echo 'Testing..'
            }
        }
        stage('Deploy') {
            steps {
                echo 'Deploying....'
            }
        }
    }
}
// Script //
node {
    stage('Build') {
        echo 'Building....'
    }
    stage('Test') {
        echo 'Building....'
    }
    stage('Deploy') {
        echo 'Deploying....'
    }
}

Not all Pipelines will have these same three stages, but it is a good starting point to define them for most projects. The sections below will demonstrate the creation and execution of a simple Pipeline in a test installation of Jenkins.

It is assumed that there is already a source control repository set up for the project and a Pipeline has been defined in Jenkins.

Using a text editor, ideally one which supports Groovy syntax highlighting, create a new Jenkinsfile in the root directory of the project.

The Declarative Pipeline example above contains the minimum necessary structure to implement a continuous delivery pipeline. The agent directive, which is required, instructs Jenkins to allocate an executor and workspace for the Pipeline. Without an agent directive, not only is the Declarative Pipeline not valid, it would not be capable of doing any work! By default the agent directive ensures that the source repository is checked out and made available for steps in the subsequent stages`

The stages directive and steps directive are also required for a valid Declarative Pipeline as they instruct Jenkins what to execute and in which stage it should be executed.

For more advanced usage with Scripted Pipeline, the example above node is a crucial first step as it allocates an executor and workspace for the Pipeline. In essence, without node, a Pipeline cannot do any work! From within node, the first order of business will be to checkout the source code for this project. Since the Jenkinsfile is being pulled directly from source control, Pipeline provides a quick and easy way to access the right revision of the source code

// Script //
node {
    checkout scm (1)
    /* .. snip .. */
}
// Declarative not yet implemented //

1	The `checkout` step will checkout code from source control; `scm` is a special variable which instructs the `checkout` step to clone the specific revision which triggered this Pipeline run.