What is the Agent Directive in Jenkins?

In Jenkins, the agent directive specifies the environment where Jenkins should execute the entire pipeline or specific stages. It can be any available node, such as a specific server, a group of servers, or execution within a Docker container.

For example:

groovy
pipeline {
    agent none // Not executed on any agent
    stages {
        stage('Build') {
            agent { docker 'maven:3-alpine' }
            steps {
                sh 'mvn clean install'
            }
        }
        stage('Test') {
            agent { label 'my-defined-label' }
            steps {
                sh 'mvn test'
            }
        }
    }
}

In this example, the Build stage executes within a specified Docker container, while the Test stage executes on a node configured with the label my-defined-label. This approach provides high flexibility and control, allowing the selection of the most suitable execution environment for different stages.