Jenkins Tweaks for Beginners - Part 2
Tags: devops, cloud, jenkins, devlive
Published: 2020-05-02 16:09:26

**Jenkins** is an open source automation tool which made CI and CD super easier to implement. But for beginners, it would take loads of time to come up with a solution for a feature. It has limitations, but comes with a wide range of plugins which would add lots of features.

 [Here ](https://blog.athreyapatel.codes/awesome-features-in-jenkins-which-makes-it-interesting-for-beginners-part-1-3b4a1440e7b1) is my Part 1 which explains on some UI tweaks which can be added to Jenkins.

## Prerequisites
As we are discussing about tweaks, All you need is:
- Basic Understanding on how to write pipelines in Jenkins.
- Basic Linux and Java skills to understand the working. 
- Groovy for scripting


## Setting up pipelines:
In Jenkins pipeline can be defined in two types of syntax

1. Declarative
2. Scripted

**Declarative** approach helps us to to write and read Pipeline code easier. It provides support for various technologies like Docker and Kubernetes. I will be using this approach.

```
pipeline {
    agent any 
    stages {
        stage('First Stage') {
            steps {
                echo 'Hello world!' 
            }
        }
        stage('Second Stage') {
            steps {
                echo 'Hello Hello world!' 
            }
        }
    }
}
``` 

**Scripted** approach was the first implementation of Pipeline as Code and is imperative programming approach.


```
node {  
    stage('First Stage'') { 
        echo 'Hello world!' 
    }
    stage('Test') { 
        echo 'Hello Hello world!'
    }
}
``` 

## Script Console 
The script console in Jenkins provides an environment to try out scripts which can be used in Jenkins without Script approval.  :laughing:
```Don't ever reload the page without copying the script ``` 

You can find the script console by navigating to 

```
YOUR_IP:PORT/script
``` 
for example:
```
107.235.18.170:8080/script
``` 

![Script Console](https://cdn.hashnode.com/res/hashnode/image/upload/v1588431551508/-Py06R2gK.png)

## Adding Parameters to Pipeline:
Parameters in Jenkins can be used to define environment variables which can be accessed in the pipeline for performing certain tasks.
> Go to your project > Configure > Checkbox "This project is parameterised"

![Adding Parameters](https://cdn.hashnode.com/res/hashnode/image/upload/v1588432152364/y33MblDI9.png)

## Snippet Generator
Snippet Generator will generate pipeline script which can be used inside the pipeline. It generates scripts for installed plugins. I have already explained in my last blog on how plugins can add features to Jenkins.

> Go to your Project > Select Pipeline Syntax from the LeftPane > Snippet Generator

#### Generate Scripts for Declarative Syntax
> Go to your Project > Select Pipeline Syntax from the LeftPane > Declarative Directive Generator

## Conclusion
Lets conclude the above learnt steps from an example

### Install Extended Choice Parameter

Manage Jenkins > Manage Plugins > Search for " [Extended Choice Parameter](https://plugins.jenkins.io/extended-choice-parameter/) " > Install without restart

Extended Choice Parameter is similar to Choice Parameter where user is provided with choice, but extended choice provides enhanced features by providing a way to use Groovy Script which can be used to return array of values.

#### Create a pipeline
> New Item > Select `Pipeline` > Enter an item name > OK
 

![Creating a Pipeline](https://cdn.hashnode.com/res/hashnode/image/upload/v1588433592890/0EIa2Xx6u.png)

Lets copy the pipeline script provided at top in declarative approach to `Pipeline script`

#### Generating extended choice parameter from Declarative Generator
In the Declarative Generator >  From the dropdown select `parameters: Parameters` > Add > extendedChoice: Extended Choice Parameter

![Extended Choice Parameter](https://cdn.hashnode.com/res/hashnode/image/upload/v1588434238489/vGU6-iaTn.png)

#### Verify the working of script in Script Console
In another tab, verify the working of the script
![Script Console](https://cdn.hashnode.com/res/hashnode/image/upload/v1588434345737/WbfCSf37a.png)

> Generate Declarative Directive from Declarative Generator and Copy

Here is the final pipeline which I can use in the Pipeline Script of the project.
```
pipeline {
    agent any 
    parameters {
      extendedChoice bindings: '', description: 'this is for the demo example', groovyClasspath: '', 
        groovyScript: '''def example = "1"
      
      if(example == "1") {
           return ["1st","2nd","3rd"]
      }''', multiSelectDelimiter: ',', name: 'example', quoteValue: false, saveJSONParameterToFile: false, type: 'PT_SINGLE_SELECT', visibleItemCount: 4
    }

    stages {
        stage('First Stage') {
            steps {
                echo 'Hello world!' 
            }
        }
        stage('Second Stage') {
            steps {
                echo 'Hello Hello world!' 
            }
        }
    }
}
``` 
Now build the Project using Build Now

After the first build, the `Build with Parameters`  replaces `Build Now`
Click on **Build with Parameters** to Select to select the parameter and **Build**

These tweaks can make Jenkins awesome for CICD pipelines and is loved by many :heart:. 

Thanks!!