Orphan steps in Otto Pipeline

After sketching out some Otto Pipeline ideas last week, I was fortunate enough to talk to a couple peers in the Jenkins community about their pipeline thoughts which led to a concept in Otto Pipelines: orphan steps. Similar to Declarative jenkins Pipelines, my initial sketches mandated a series of stage blocks to encapsulate behavior. Steven Terrana, author of the Jenkins Templating Engine made a provocative suggestion: “stages should be optional.”

It is always refreshing when somebody asks “but why have we always done it this way?” and without a good answer, you find yourself asking the same question.

As best as I can remember, Declarative Pipeline requires the stages in order to make rendering of pipelines prettier in Blue Ocean. The utility of stages for complex pipelines is pretty clear, but for the simpler pipelines, they end up adding unnecessary boilerplate. The following is the smallest possible Declarative Jenkins Pipeline needed to run make:

pipeline {
    agent any

    stages {
        stage('Build') {
            steps {
                sh 'make'
            }
        }
    }
}

With the addition to orphan steps in Otto Pipelines, the smallest possible invocation becomes:

use stdlib
pipeline {
  steps {
    sh 'make'
  }
}

The more I thought about orphan steps, the more I liked them. A stage can provide scoped options like

  • Environment variables
  • Runtime environment
  • Credentials
  • Gates
  • Post-stage conditions

If you don’t need any of the trappings or other capabilities that a stage provides, why bother with the extra boilerplate! The pipeline execution is already sequential, orphan steps will execute linearly just like any sequence of stages would. An example:

use stdlib

pipeline {
  steps {
    sh 'bundle exec rake spec package'
    archive artifacts: 'pkg/*.gem', name: 'gems'
  }

  stage {
    name = 'Publish to rubygems'
    credentials = ['rubygems-token']
    steps {
      unarchive 'gems'
      gemupload gems: 'pkg/*.gem'
    }
  }

  steps {
    echo '>> Any cleanup?'
  }
}

Freeing my mind from the burden of considering “everything must be a stage” allowed me to also consider other top level “verbs” that make sense within the pipeline [ }. A rough list of what I am currently thinking would be:

  • steps, orphan steps.
  • stage, container of more configuration to execute steps.
  • fanout, container of multiple stages to run in parallel, failing immediately if a branch fails.
  • parallel, container of multiple stages to run in parallel.
  • confirm, prompt a user to confirm that the pipeline can continue.
  • prompt, prompt the user for a parameter(s) which can be saved into a variable.
  • rollback, execute some steps if some event indicating a failure is fired in the Otto event system.

Quoting Steven again: “it’s better to have different names for different behaviors, rather than a bunch of configuration options.” This gist contains a rough sketch of what some of those verbs would look like.

At this point I am quite excited by the aesthetics of the pipeline with these rich descriptive blocks. This approach doesn’t result in significantly more parser and implementation work, but it does have the potential to make Otto Pipelines more clear in their behavior, which is fantastic.

The syntax shared above is far from final, but I cannot wait to get some of this implemented to try out with real workloads!