Day 26: Jenkins Declarative Pipeline

One of the most important parts of your DevOps and CICD journey is a Declarative Pipeline Syntax of Jenkins

Some terms for your Knowledge

What is Pipeline - A pipeline is a collection of steps or jobs interlinked in a sequence.

Declarative: Declarative is a more recent and advanced implementation of a pipeline as a code.

Scripted: Scripted was the first and most traditional implementation of the pipeline as a code in Jenkins. It was designed as a general-purpose DSL (Domain Specific Language) built with Groovy.

Why you should have a Pipeline

The definition of a Jenkins Pipeline is written into a text file (called a Jenkinsfile) which in turn can be committed to a project’s source control repository.
This is the foundation of "Pipeline-as-code"; treating the CD pipeline as a part of the application to be versioned and reviewed like any other code.

Creating a Jenkinsfile and committing it to source control provides a number of immediate benefits:

• Automatically creates a Pipeline build process for all branches and pull requests.

• Code review/iteration on the Pipeline (along with the remaining source code).

Pipeline syntax

pipeline {
    agent any 
    stages {
        stage('Build') { 
            steps {
                // 
            }
        }
        stage('Test') { 
            steps {
                // 
            }
        }
        stage('Deploy') { 
            steps {
                // 
            }
        }
    }
}

Task-01: Jenkins "Hello World" Declarative Pipeline

• Create a New Job, this time select Pipeline instead of Freestyle Project.

1. Click on "New Item" to create a new Jenkins job.

2. Enter Job Details:

   • Provide a name for the job (e.g., "HelloWorldPipeline").

   • Choose "Pipeline" as the job type.

Configure Pipeline: In the pipeline configuration section:

• Choose "Pipeline script" from the "Definition" drop-down.

• In the "Pipeline" section, you can directly enter the Declarative pipeline script.

Add Declarative Pipeline Script: Use the following example as your Declarative pipeline script:

 pipeline {
    agent any
    stages {
        stage('Hello') {
            steps {
                echo 'Hello World!'
            }
        }
    }
}

Save and Run:

• Click on "Save" to save your pipeline configuration.

• Run the pipeline job by clicking on "Build Now."

View Console Output: After the build completes, you can click on the build number to view the console output. You'll see the output "Hello World!" printed as part of the pipeline execution.

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