Docker with Environment Variables

In this tutorial, we will learn how to use environment variables to make our Jenkins pipeline more dynamic and maintainable. We will define variables for Docker image names, tags, credentials, and ports, and use them throughout the pipeline.

Jenkinsfile

Here is the complete Jenkinsfile. You can find the source code in the GitHub repository.

pipeline {
  agent any
  options {
    disableConcurrentBuilds()
    disableResume()
    buildDiscarder(logRotator(numToKeepStr: '10'))
    timeout(time: 1, unit: 'HOURS')
  }
  tools {
    maven 'maven-3.6.3' 
  }
  parameters {
    choice(name: 'ENVIRONMENT', choices: ['dev', 'qa', 'prod'], description: 'Choose Environment')
  }
  environment {
    DOCKER_CREDENTIAL_ID = "docker-credential"
    SSH_CREDENTIAL_ID = "ssh-pass-credential"
    DOCKER_USERNAME = "vigneshsweekaran"
    IMAGE_NAME = "hello-world-java"
    IMAGE_TAG = "1.${BUILD_NUMBER}"
    CONTAINER_NAME = "hello-world-java"
    HOST_PORT = "8080"
    CONTAINER_PORT = "8080"
  }
  stages {
    stage ('Build') {
      steps {
        sh "mvn clean package"
      }
    }
    stage ('Docker Build') {
      steps {
        sh "docker build -t ${IMAGE_NAME}:${IMAGE_TAG} ."
      }
    }
    stage ('Docker Push') {
      steps {
        withCredentials([usernamePassword(credentialsId: "${DOCKER_CREDENTIAL_ID}", passwordVariable: 'DOCKER_PASSWORD', usernameVariable: 'DOCKER_USERNAME')]) {
          sh """
            echo ${DOCKER_PASSWORD} | docker login -u ${DOCKER_USERNAME} --password-stdin
            docker tag ${IMAGE_NAME}:${IMAGE_TAG} ${DOCKER_USERNAME}/${IMAGE_NAME}:${IMAGE_TAG}
            docker push ${DOCKER_USERNAME}/${IMAGE_NAME}:${IMAGE_TAG}
            docker logout
          """
        }
      }
    }
    stage ('Deploy to Dev') {
      when {
        environment name: "ENVIRONMENT", value: "dev"
      }
      steps {
        script {
          withCredentials([usernamePassword(credentialsId: "${SSH_CREDENTIAL_ID}", passwordVariable: 'SSH_PASSWORD', usernameVariable: 'SSH_USERNAME')]) {
            def remote = [:]
            remote.name = 'test'
            remote.host = '20.193.155.41'
            remote.user = "${SSH_USERNAME}"
            remote.password = "${SSH_PASSWORD}"
            remote.allowAnyHosts = true
            sshCommand remote: remote, command: "docker rm -f ${CONTAINER_NAME} || true && docker run -d --name ${CONTAINER_NAME} -p ${HOST_PORT}:${CONTAINER_PORT} ${DOCKER_USERNAME}/${IMAGE_NAME}:${IMAGE_TAG}"
          }
        }
      }
    }
    stage ('Deploy to Qa') {
      when {
        environment name: "ENVIRONMENT", value: "qa"
      }
      steps {
        script {
          withCredentials([usernamePassword(credentialsId: "${SSH_CREDENTIAL_ID}", passwordVariable: 'SSH_PASSWORD', usernameVariable: 'SSH_USERNAME')]) {
            def remote = [:]
            remote.name = 'test'
            remote.host = '20.197.20.30'
            remote.user = "${SSH_USERNAME}"
            remote.password = "${SSH_PASSWORD}"
            remote.allowAnyHosts = true
            sshCommand remote: remote, command: "docker rm -f ${CONTAINER_NAME} || true && docker run -d --name ${CONTAINER_NAME} -p ${HOST_PORT}:${CONTAINER_PORT} ${DOCKER_USERNAME}/${IMAGE_NAME}:${IMAGE_TAG}"
          }
        }
      }
    }
    stage ('Deploy to Prod') {
      when {
        environment name: "ENVIRONMENT", value: "prod"
      }
      steps {
        script {
          withCredentials([usernamePassword(credentialsId: "${SSH_CREDENTIAL_ID}", passwordVariable: 'SSH_PASSWORD', usernameVariable: 'SSH_USERNAME')]) {
            def remote = [:]
            remote.name = 'test'
            remote.host = '20.197.20.178'
            remote.user = "${SSH_USERNAME}"
            remote.password = "${SSH_PASSWORD}"
            remote.allowAnyHosts = true
            sshCommand remote: remote, command: "docker rm -f ${CONTAINER_NAME} || true && docker run -d --name ${CONTAINER_NAME} -p ${HOST_PORT}:${CONTAINER_PORT} ${DOCKER_USERNAME}/${IMAGE_NAME}:${IMAGE_TAG}"
          }
        }
      }
    }
  }
  post {
    always {
      deleteDir()
    }
  }
}

Explanation

Environment Block

The environment block is used to define global variables available to all stages. - IMAGE_NAME, IMAGE_TAG: Define the Docker image details. - CONTAINER_NAME: Defines the name of the running container. - HOST_PORT, CONTAINER_PORT: Define port mapping.

By using these variables (e.g., ${IMAGE_NAME}), we avoid hardcoding values in multiple places, making the pipeline easier to update.

Shell Steps

In the sh steps, we reference these variables using the standard Groovy string interpolation ${VARIABLE_NAME}.

Important Tips

Tip

Single Source of Truth: By defining IMAGE_TAG in the environment block (e.g., 1.${BUILD_NUMBER}), you guarantee that the same version tag is used for building, pushing, and deploying across all stages.

Note

Shell Interpolation: When using sh steps, use double quotes " if you want Jenkins to interpolate variables (like ${IMAGE_NAME}). Use single quotes ' if you want the shell to handle the variable (like $PATH).

Quick Quiz

#

What is the primary benefit of using the environment block in a Jenkinsfile?

To avoid hardcoding values and improve maintainability

To speed up the build process

To encrypt sensitive data

To define the agent type

The environment block allows you to define variables in one place and reuse them throughout the pipeline, making it easier to manage and update configurations.

#

How do you interpolate a variable in a Groovy string (double quotes)?

${VARIABLE}

$(VARIABLE)

%VARIABLE%

{{VARIABLE}}

Groovy GStrings allow variable interpolation using the ${} syntax (not to be confused with shell variable expansion $VAR).

#

What is the scope of variables defined in the top-level environment block?

Global to the entire pipeline

Local to the first stage only

Local to the agent

Only available in the post block

Variables defined at the top level of the pipeline block are accessible in all stages and steps within that pipeline.

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