can my Jenkinsfile contain only properties and no piepeline code - jenkins

Question

All the tutorials that I have come across regarding writing a declarative pipeline suggest to include the stages and steps in the Jenkinsfile.
But I have noticed one of my seniors writing it the opposite way. He uses the Jenkinsfile just for defining all the properties, i.e. his Jenkinsfile is just a properties file, nothing more nothing less.
And for defining the pipeline he makes use of the shared library concepts where he writes his pipeline code in a file in the vars folder. I am not able to guess the wisdom behind this approach.
Nowhere over the internet did I come across anything similar.
Any guidance in this regard is highly appreciated. I am a beginner in the Jenkins world.

Answer 1

As illustrated in Extending with Shared Libraries, that approach (that I am using as well) allows to:
keep a Jenkinsfile content to a minimum
enforce a standard way of doing a particular job (as coded in the shared library)
That shared library becomes a template of a process for which you provide only values in your Jenkinsfile before delegating the actual execution to the pre-defined library.
The OP Asif Kamran Malick note that the documentation does include:
There is also a “builder pattern” trick using Groovy’s Closure.DELEGATE_FIRST, which permits Jenkinsfile to look slightly more like a configuration file than a program, but this is more complex and error-prone and is not recommended.
He then asks:
Why did the blogger prefer that way when its actually discouraged in the official doc.
I checked and we are using also Closure.DELEGATE_FIRST.
The reason is in the part "permits Jenkinsfile to look slightly more like a configuration file than a program"
This avoids us having to define a JSON block, and keep the parameter as a series of key=value lines, easier to read.
A call to a shared library is then:
#!/usr/bin/env groovy
#Library("MyLibraries") _
MyLibrary {
config1 = 'value1'
config2 = 'value2'
...
}
{
anotherConfigA = 'valueA'
anotherConfigB = 'valueB'...
astep(
...
)
}
Then your jenkins pipeline template in MyLibraries/vars/MyLibrary.yml can use those closure blocks:
def call(Closure configBlock, Closure body) {
def config = [:]
configBlock.resolveStrategy = Closure.DELEGATE_FIRST
configBlock.delegate = config
configBlock()
astep(
...
){
if (body) { body() }
}
}