In the Jenkins pipeline, we have two ways of writing Jenkinsfile,
- Scripted – The Older way of writing Jenkinsfile, we have to write a lot of logic using Groovy
- Declarative – Newer and easier way, comes with a lot of inbuilt functions (also called steps)
Scripted
In the Scripted way, the Jenkinsfile starts with the node block
node {
}Declarative
In the Declarative way, the Jenkinsfile starts with the pipeline block (Mandatory)
pipeline {
}Declarative Jenkinsfile in detail
Basic Structure
- Inside the pipeline block, we have an agent block
(Mandatory)and stages block(Mandatory) - Inside the stages block, we should have at least one stage block
- Inside the stage block, we should have steps block
- Inside the steps block, we should have at least one step (inbuild function name)
E.g.- sh step to execute any shell commands
- echo step to print some data
pipeline {
agent any
stages {
stage ('Print') {
steps {
echo "Hello Devops Engineers"
}
}
}
}- agent block is used to tell Jenkins where to execute this Pipeline. It executes in the same Jenkins server ( Controller ) by default.
If we have configured agents for Jenkins ( additional servers only for building the pipelines ), then we can use this agent block to tell Jenkins where to execute this pipeline. - stage block is used to group the set of tasks and visualize in the Pipeline Dashboard
- steps block is used to group the step
- step is the basic unit that executes the command.
In the above Jenkinsfile, we have created the Print stage which uses the echo step to print Hello Devops Engineers
Post block in Jenkinsfile
The post block is inside a pipeline block. This block is executed once all stages are completed
pipeline {
agent any
stages {
stage ('Print') {
steps {
echo "Hello Devops Engineers"
}
}
}
post {
always {
echo 'I will always say Hello again!'
}
success {
echo 'I will say Hello only if job is success'
}
failure {
echo 'I will say Hello only if job is failure'
}
}
}In post block, we have three subblocks always, success and failure
- always – If we trigger a job, whether the stage is success or failure, this block will always be executed.
- success – This block will be executed only if all the stages are passed.
- failure – This block will be executed if any one of the stages is failed.
Triggers block in Jenkinsfile
The triggers block is inside a pipeline block. Which is used to define how the pipeline should be triggered
These are some options for triggers cron, pollSCM, upstream, and githubPush
cron
Accepts a cron-style string to define a regular interval at which the Pipeline should be triggered
triggers {
cron('H/15 * * * *')
}This will trigger the pipeline every fifteen minutes
pollSCM
Accepts a cron-style string to define a regular interval at which Jenkins should check for new source code changes.
If any new changes exist, the Pipeline will be triggered else skipped.
triggers {
pollSCM('* * * * *')
}This will check for new source code changes in the Git repository every minute.
upstream
Accepts a comma-separated string of jobs and a threshold. When any job in the string finishes with the minimum threshold, the Pipeline will be triggered.
triggers {
upstream(upstreamProjects: 'Pipeline-1,Pipeline-2', threshold: hudson.model.Result.SUCCESS)
}This will trigger the pipeline if Pipeline-1 or Pipeline-2 is finished with SUCCESS status.
Jenkinsfile with cron triggers
pipeline {
agent any
triggers {
cron('H/15 * * * *')
}
stages {
stage ('Print') {
steps {
echo "Hello Devops Engineers"
}
}
}
post {
always {
echo 'I will always say Hello again!'
}
success {
echo 'I will say Hello only if job is success'
}
failure {
echo 'I will say Hello only if job is failure'
}
}
}Parameters block in Jenkinsfile
The parameters block is inside a pipeline block.
The parameters block is used to pass dynamic parameters/variables to the Pipeline.
It has the following types
string
text
booleanParam
choice
password
string
A parameter of a string type
parameters {
string(name: 'ENVIRONMENT', defaultValue: 'dev', description: 'Type Environment name to deploy')
}text
A text parameter can contain multiple lines
parameters {
text(name: 'DEPLOY_TEXT', defaultValue: 'One\nTwo\nThree\n', description: 'Multi line string')
}booleanParam
A boolean parameter
parameters {
booleanParam(name: 'ENABLE_DEBUG', defaultValue: true, description: 'Enable debugging logs')
}choice
A choice parameter
parameters {
choice(name: 'ENVIRONMENT', choices: ['dev', 'qa', 'prod'], description: 'Choose Environment to deploy')
}password
A password parameter
parameters {
password(name: 'SERVER_PASSWORD', defaultValue: '***', description: 'Server SSH password')
}Jenkinsfile with parameters
pipeline {
agent any
triggers {
cron('H/15 * * * *')
}
parameters {
choice(name: 'ENVIRONMENT', choices: ['dev', 'qa', 'prod'], description: 'Select Environment to deploy')
}
stages {
stage ('Print') {
steps {
echo "Hello Devops Engineers"
}
}
}
post {
always {
echo 'I will always say Hello again!'
}
success {
echo 'I will say Hello only if job is success'
}
failure {
echo 'I will say Hello only if job is failure'
}
}
}Environment block in Jenkinsfile
The environment block specifies a sequence of key-value pairs that will be available as environment variables inside the steps block
The environment block can be inside the pipeline block or inside the stage block
pipeline {
agent any
environment {
DESIGNATION = 'Devops Engineer'
}
triggers {
cron('H/15 * * * *')
}
parameters {
choice(name: 'ENVIRONMENT', choices: ['dev', 'qa', 'prod'], description: 'Select Environment to deploy')
}
stages {
stage ('Print') {
environment {
MESSAGE = 'Hello Devops Engineers'
}
steps {
echo "Your Designation is $DESIGNATION"
echo "$MESSAGE"
}
}
}
post {
always {
echo 'I will always say Hello again!'
}
success {
echo 'I will say Hello only if job is success'
}
failure {
echo 'I will say Hello only if job is failure'
}
}
}If environment block is defined within the stage block, then those environment variables will be accessible only within that stage.