Jenkins is one of the most popular CICD tools, which is entirely open-source. In this blog, we will understand what Jenkins workflow is. We will also understand the basics of the Jenkins pipeline and different ways to define a pipeline. So let’s get started.
What is Jenkins
Jenkins is an open-source CI-CD tool that software developer uses for continuous integration and continuous development. Jenkins is written in java and follows the complete life cycle of software from development to testing to deployment.
Jenkins is one of the most popular and widely used applications whose popularity grows day by day. Companies can accelerate their software development process by using Jenkins, as Jenkins can automate build and tests rapidly.
There are many ways to install Jenkins in your system
- Installation of a physical machine
- Installed via docker container
- Installed on top of Kubernetes
- Installed on Kubernetes as an operator(Jenkins operator)
What is Jenkins workflow
Jenkins workflow is the old name for the Jenkins pipeline. Pipelines are the Jenkins job which a user-defined programmatically using the groovy script
To create a pipeline goto Jenkins > New item > Pipeline
Give a proper name and click on OK
What is Jenkins pipeline
In Jenkins, a pipeline is simply a collection of events or jobs that might be interlinked together in a sequence.
As per the official pipeline definition, Jenkins Pipeline is a suite of plugins that supports implementing and integrating continuous delivery pipelines into Jenkins. Pipeline provides an extensible set of tools for modeling simple-to-complex delivery pipelines “as code” via the Pipeline DSL.
There are many advantages of defining Jenkins job via pipeline:
- Jenkins pipeline enables you to define the Jenkins job via pipeline which is easy to maintain and review.
- Jenkins pipelines are robust and pipelines will be secure even if the server undergoes an unpredicted restart.
- With Jenkins Pipelines, you can add CI-CD to big projects as well as with Jenkins pipelines you can run multiple jobs.
Jenkins pipeline plugin
Jenkins Pipeline is a very powerful plugin that enables continuous delivery pipelines in Jenkins. The pipeline plugin helps to define the steps involved in a delivery pipeline as code, known as a “Jenkinsfile”. The Jenkinsfile can be stored in a source control system like Git.
The pipeline is defined using a Domain Specific Language (DSL) in Groovy, which provides a rich set of pre-defined steps and functions.
Jenkins Pipeline also provides visualization of the pipeline and its status, making it easier to understand the flow of the delivery process, as well as the status of each stage and step. The pipeline plugin also integrates with other Jenkins plugins, such as the Git plugin, allowing pipelines to be triggered automatically when changes are pushed to a Git repository.
Jenkins pipeline syntax
Jenkins supports two types of pipeline declaration
- Declarative Pipeline
- Scripted pipeline
Both declarative, as well as scripted pipelines, should define a predefined syntax to define the pipeline. The Jenkins scripted pipeline should start with a node, whereas Jenkins declarative pipeline should start with a pipeline block.
Some of the widely used sections in the Jenkins pipelines are:-
- Agent
- post
- Stages
- steps
Jenkins pipeline agent
The agent session in the Jenkins pipeline specifies where the entire Jenkins or Jenkins stage will run. The agent session must be defined on top of pipelines but are optional in the stage label. The agent in the Jenkins pipeline can be:
- Any
- none
- label
- node
- Docker
- dockerfile
- Kubernetes
More information about the Jenkins agents can be found here
Jenkins pipeline stages
The stage session is where you define your work in the Jenkins pipeline. The Jenkins stages block consists of one or more stage blocks. Below is a sample Jenkins pipeline with a single-stage
pipeline {
agent any
stages {
stage('Example') {
steps {
echo 'Hello World'
}
}
}
}You can check my below blogs to learn more about the stages block
Jenkins pipeline Multiple stages
Jenkins pipeline syntax generator
Jenkins provides a very powerful and valuable tool to get the syntax for your Jenkins pipeline. The syntax generator tool can be found under
http://<jenkins_url>/directive-generator/Once you go to the above URL, the below UI will open
The syntax generator tool is straightforward to use. You can go ahead and try to generate the syntax for your Jenkins pipeline based on your use case.
Let’s understand how we can use the syntax generator tool to generate the when condition pipeline.
In the simple directive, select when a condition, and inside the when condition select anyof and checkmark the Evaluate before option and then click on Generative Declarative directive to generate the pipeline syntax.
The syntax generator tool has generated the below syntax, which we can use in our pipeline declaration. This tool displays the code and points us to the official documentation link.
Jenkins Declarative Pipeline
The Jenkins declarative pipeline was recently added to the Jenkins pipeline. It follows a very simple syntax on top of the Pipeline sub-systems.
All Declarative Pipelines must be enclosed within a pipeline block
pipeline {
/* insert Declarative Pipeline here */
}The declarative pipeline is relatively new, so there are limitations on the size of code within the pipeline{} block.
The various components of the JenkinsDeclarative Pipeline are:
- Agent
- post
- stages
- steps
Jenkins scripted pipeline
The scripted pipeline is a general-purpose DSL build on groovy. Most functionality of groovy is made available to users of scripted pipelines. The other advantage of scripted pipelines is that they are very flexible and expressive.
LikeDeclarative Pipelines, scripted pipelines also have stages and steps definitions.
You can check this link to understand the syntax difference betweendeclarative andscripted pipelines.
Jenkins pipeline example
We will see the basic JenkinsDeclarative andscripted pipeline examples in this session.
Jenkins declarative pipeline example groovy
The Jenkinsdeclarative pipeline follows the below syntax:
pipeline {
agent none
stages {
stage('Build') {
steps {
echo 'Hello World!!'
}
}
stage('Deploy') {
when {
beforeInput true
branch 'production'
}
input {
message "Deploy to production?"
id "simple-input"
}
steps {
echo 'Deploying'
}
}
}
}Jenkins scripted pipeline example.
Jenkins scripted pipeline uses domain-specific language like groovy to define your Jenkins job in the form of the pipeline. The Jenkins scripted pipeline follows the below syntax.
node {
stage('Test') {
if (env.BRANCH_NAME == 'master') {
echo 'execute on the master branch'
} else {
echo 'execute elsewhere'
}
}
}Please read my blog on Jenkins scripted pipeline to get a complete understanding of the scripted pipeline.
Jenkins pipeline multiple agents
So far, we have used Jenkins with a single agent. But users can define the Jenkins pipeline to run on multiple agents. Building pipelines in multiple agents can benefit advanced use cases such as executing builds/tests across various platforms.
Below is the Jenkins pipeline with multiple agents defined for each stage.
The agent is none for the builds stage. None means using any available agent.
In the Linux test step, select an agent whose label matches Linux, and in thewindows test step, select an agent whose label matches windows
pipeline {
agent none
stages {
stage('Build') {
agent any
steps {
echo 'Build stage'
}
}
stage('Test on Linux') {
agent {
label 'linux'
}
steps {
echo 'Testing script on linux agent'
}
}
stage('Test on Windows') {
agent {
label 'windows'
}
steps {
echo 'Testing script on Windows agent'
}
}
}
}Conclusion
I hope you like this small tutorial on Jenkins workflow. There has been a lot of new functionality added to Jenkin’s latest version. I recommend you check my other blogs on Jenkins to get familiar with recent development.
Please do let me know if you are facing any issues while following along
