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Declarative Syntax Basics

Setup to use Blue Ocean Pipeline Editor

Note: You need to have a Github personal access token (Github-Personal-Access-Token.md) before proceeding.

We will setup the Blue Ocean Pipeline Editor so we can use the visual editor for many of following exercises:

  1. If not already in Blue Ocean, click on the Teams or Open Blue Ocean link in the left side navigation bar
  2. Click on the Create a new Pipeline button (if you have already created a Pipeline, you will need to click the New Pipeline button in the upper right)

  3. Click on one of the options in the Where do you store your code? section (GitHub for this course)

  4. Enter your GitHub token (your GitHub Personal Access Token)
  5. Next, select your GitHub user account (NOTE: Be sure to select the GitHub Organization where you created the empty repository for this workshop. The repository should not have an existing Jenkinsfile.)

  6. Under Choose a repository select the repository you created during setup and then click the Create Pipeline button

Next, the Blue Ocean editor will open - if the editor does not load after a minute or so, refresh your browser.

Basic Declarative Syntax Structure

In this exercise we will create a simple Declarative Pipeline using the Blue Ocen Pipeline editor.

Declarative Pipelines must be enclosed within a pipeline block and must contain a top-level agent declaration, and then contains exactly one stages block. The stages block must have at least one stage block but can have an unlimited number of additional stages. Each stage block must have exactly one steps block. The Blue Ocean editor takes care of much of this for you but we will need to add a stage and steps.

Using the Blue Ocean Pipeline editor we setup in the previous exercise, do the following:

  1. You should see the You don't have any branches that contain a Jenkinsfile dialog, click on the Create Pipeline button (NOTE: If you already had a Jenkinsfile in your repository then the editor should open straight-away)

  2. Click on the + icon next to the pipeline's Start node to add a stage

  3. Click into Name your stage and type in the text 'Say Hello'
  4. Click on the + Add step button

  5. Click on the Print Message step and type in Hello World! as the Message
  6. Click on the <- (arrow) next to the 'Say Hello / Print Message' text to add another step

  7. Click on the + Add step button
  8. Click on the Shell Script step and enter java -version into the text area
  9. Press the key combination CTRL + S to open the Blue Ocean free-form editor and you should see a Pipeline similar to the one below (click anywhere outside the editor to close it):
pipeline {
   agent any
   stages {
      stage('Say Hello') {
         steps {
            echo 'Hello World!'   
            sh 'java -version'
         }
      }
   }
}
  1. Click the Save button

  2. Enter a commit message into the Save Pipeline pop up and click Save & Run

Your Pipeline is actually being committed and pushed to your GitHub repository, and will run right away.

  1. Click on your Pipeline to see the steps execute.

  2. Expand the **'java -version — Shell Script' step and you should see the following:

NOTE: You may have noticed that your Pipeline GitHub repository is being cloned even though you didn't specify that in your Jenkinsfile. Declarative Pipeline checks out source code by default.

Agent Labels

In this exercise we will update the pipeline we created in the previous exercise to use a specific agent using the label syntax. As you saw from the build logs of the previous exercise, the Java version of the agent any was 8. We want to update our pipeline to use a version 9 JDK by replacing the any parameter with a label declaration:

  1. Click on the pencil icon in the top right to edit your Pipeline

  2. Use the key combination CTRL + S to open up the free-form editor

NOTE: You could use the visual editor but it doesn't support the short syntax for adding a label and requires you to add a node block and then apply a label

  1. Replace the agent any declaration with the following agent declaration:

NOTE: Don't worry about formatting too much as the Blue Ocean editor will reformat your Jenkinsfile before it is committed to your repository

  agent {
    label 'jdk9'
  }
  1. Click the Update button
  2. Click the Save button, enter a commit message into the Save Pipeline pop up and click Save & Run.

You should see the following output for the sh step after your Pipeline runs:

openjdk version "9.0.4"
OpenJDK Runtime Environment (build 9.0.4+12-Debian-4)
OpenJDK 64-Bit Server VM (build 9.0.4+12-Debian-4, mixed mode)

In addition to any and label you may also specify none and no global agent will be allocated for the entire Pipeline run and each stage section will need to contain its own agent section.

  1. Now change the value of the label to default
   agent {
     label 'jdk8'
   }
  1. Click the Save button, enter a commit message into the Save Pipeline pop up and click Save & Run.

You should see the following output for the sh step after your updated Pipeline runs:

openjdk version "1.8.0_151"
OpenJDK Runtime Environment (IcedTea 3.6.0) (Alpine 8.151.12-r0)
OpenJDK 64-Bit Server VM (build 25.151-b12, mixed mode)

Your Pipeline should look like the following before you move onto the next exercise:

pipeline {
   agent { label 'jdk8' }
   stages {
      stage('Say Hello') {
         steps {
            echo 'Hello World!'   
            sh 'java -version'
         }
      }
   }
}

Environment Directive

For this exercise we are going to update our pipeline to demonstrate how to use the environment directive to set and use environment variables. We will also see how this directive supports a special helper method credentials() that allows access to pre-defined Jenkins Credentials based on their id.

Simple Environment Variables

  1. At the top of the pipeline insert the following code between the agent and stages blocks:
   environment {
      MY_NAME = 'Mary'
   }
  1. Then update the echo 'Hello World!' line to read echo "Hello ${MY_NAME}!"

Notice the change from '' to "". Using double quotes will trigger extrapolation of environment variables.

  1. Click the Update button
  2. Click the Save button, enter a commit message into the Save Pipeline pop up and click Save & Run.
  3. Click on your Pipeline to see the steps execute.

NOTE: The Blue Ocean Editor will move global environment blocks after stages. The location does not matter as long as it is outside the stages block.

Credentials

We can also use environmental variables to import credentials.

  1. Add the following line to our environment block:

TEST_USER = credentials('test-user')

NOTE: For Credentials which are of type "Standard username and password", the environment variable specified will be set to username:password and two additional environment variables will automatically be defined: MYVARNAME_USR and MYVARNAME_PSW respectively.

  1. Add the following echo steps within the steps of the Say Hello stage:
            echo "${TEST_USER_USR}"
            echo "${TEST_USER_PSW}"
  1. Click the Update button
  2. Click the Save button, enter a commit message into the Save Pipeline pop up and click Save & Run.
  3. Click on your Pipeline to see the steps execute. Look at the console output and make note of the fact that the credential user name and password are masked when output via the echo command.

Parameters

In this exercise we will update our pipeline to accept external input in the form of a Jenkins job parameter.

  1. Update your pipeline by inserting the following after the environment block:
   parameters {
      string(name: 'Name', defaultValue: 'whoever you are', 
	     description: 'Who should I say hi to?')
   }
  1. Update the echo "Hello ${MY_NAME}!' line to read echo "Hello ${params.Name}!"
  2. Click the Save button, enter a commit message into the Save Pipeline pop up and click Save & Run.

NOTE: The option to Build with parameters will not be available until you run your job at least once as parameters are Jenkins job properties that must be set in Jenkins. Using parameters in your Jenkinsfile updates the Jenking job configuration after the first run.

  1. Run the pipeline again by returning to the Blue Ocean activity view and then clicking on the Branches tab top right and then click the run button.

  2. After clicking the run button an Input required dialog will appear with the Name paramter. Replace whoever you are with your name and click the Run button.

  3. Now your top Print Message step should reflect your parameter value similar to this for a value of Beedemo Dev:

Next Exercises

You may proceed onto Declarative Advanced Syntax once your instructor tells you to.

Before you proceed you may want to check that your Pipeline looks like the following:

pipeline {
  agent {
    label 'jdk8'
  }
  stages {
    stage('Say Hello') {
      steps {
        echo "Hello ${params.Name}!"
        sh 'java -version'
        echo "${TEST_USER_USR}"
        echo "${TEST_USER_PSW}"
      }
    }
  }
  environment {
    MY_NAME = 'Mary'
    TEST_USER = credentials('test-user')
  }
  parameters {
    string(name: 'Name', defaultValue: 'whoever you are', description: 'Who should I say hi to?')
  }
}