How can i use 'parallel' option in jenkins pipeline in the 'post' section? - jenkins

Question

I looked at many pipeline examples and how to write the post build section in a pipeline script. But never got my answer i was looking for.
I have 4 jobs - say Job A,B,C and D. I want job A to run first, and if successful it should trigger Job B,C,D in parallel. If Job A fails, it should trigger only Job B. Something like below:
pipeline {
agent any
stages {
stage('Build_1') {
steps {
sh '''
Build Job A
'''
}
}
post {
failure {
sh '''
Build Job B
'''
}
success {
sh '''
Build Job B,C,D in parallel
'''
}
}
}
I tried using 'parallel' option in post section but it gave me errors. Is there a way to build Job B,C,D in parallel, in the post 'success' section?
Thanks in advance!

Answer 1

The parallel keyword actually can work inside a post condition as long as it is encapsulated inside a script block, as the script blocks is just a fallback to the scripted pipeline which will allow you to run parallel execution step wherever you want.
The following should work fine:
pipeline {
agent any
stages {
stage('Build_1') {
steps {
// Build Job A
}
}
}
post {
failure {
// run job B
build job: 'Job-B'
}
success {
script {
// run jobs B, C, D in parallel
def jobs = ['Job-B', 'Job-C', 'Job-D']
parallel jobs.collectEntries { job ->
["Building ${job}" : {
build job: job
}]
}
}
}
}
}
This is just an example and specific parameters or configuration (for the build keyword) can be added to each job execution according to your needs.

Answer 2

The error message is quiet clear about this:
Invalid step "parallel" used - not allowed in this context - The
parallel step can only be used as the only top-level step in a stages
step
The more restrictive declarative syntax does not allow the usage of parallel in thw post section at the moment.
If you don't want to switch to the scripted syntax, another option that should work: Build the jobs B,C,D in parallel in a second stage and move the the failure condition in the post section of your first stage. As a result job B,C,D will run if A is successful. If A is not successful only job B will run.
pipeline {
agent any
stages {
stage('one') {
steps {
// run job A
}
post {
failure {
// run job B
}
}
}
stage('two') {
steps {
parallel(
// run job B, C, D
)
}
}
}
}