What is Jenkins Pipeline & Its Best Practices

What is a Jenkins pipeline?

A pipeline is a collection of jobs that brings the software from version control into the hands of the end users by using automation tools. It is a feature used to incorporate continuous delivery in software development workflow.

Pipeline Concepts

The below fundamentals are common to both, scripted and declarative pipeline:

1.    Pipeline: A user-defined block which contains all the stages. It is a key part of declarative pipeline syntax.

2.    Node: A node is a machine that executes an entire workflow. It is a key part of the scripted pipeline syntax.

3.   Agent: instructs Jenkins to allocate an executor for the builds. It is defined for an entire pipeline or a specific stage.

It has the following parameters:

·       Any: Runs pipeline/ stage on any available agent

·     None: applied at the root of the pipeline, it indicates that there is no global agent for the entire pipeline & each stage must specify its own agent

·       Label: Executes the pipeline/stage on the labelled agent.

·   Docker: Uses docker container as an execution environment for the pipeline or a specific stage.

1.   Stages: It contains all the work; each stage performs a specific task.

2.   Steps: steps are carried out in sequence to execute a stage

Jenkins Pipeline syntax example

 

pipeline{

     stage(‘SCM checkout’) {

          //Checkout from your SCM(Source Control Management)

          //For eg: Git Checkout

     }

     stage(‘Build’) {

          //Compile code

          //Install dependencies

          //Perform Unit Test, Integration Test

     }

     stage(‘Test’) {

          //Resolve test server dependencies

          //Perform UAT

     }

     stage(‘Deploy’) {

          //Deploy code to prod server

          //Solve dependency issues

     }

}

 

Schedule a build periodically

Jenkins uses Cron expressions to schedule a job. Each line consists of 5 fields separated by TAB or whitespace:

 

Syntax: (Minute Hour DOM Month DOW)

MINUTE: Minutes in one hour (0-59)

HOURS: Hours in one day (0-23)

DAYMONTH: Day in a month (1-31)

MONTH: Month in a year (1-12)

DAYWEEK: Day of the week (0-7) where 0 and 7 are sunday

Example: H/2 * * * * (schedule your build for every 2 minutes) 

Build Shared library for reusable logic

Refer this link

Common Mistakes to avoid in Jenkins

1.    Not storing pipeline code in Jenkinsfile

2.    Blocking Executor and waiting for Input

3. Repetition of similar pipeline steps

4. Creating large global variable declarations

Best Practices - https://www.jenkins.io/doc/book/pipeline/pipeline-best-practices/