How to Build Dynamic Parallel Branches in Jenkins

The parallel step accepts a map of name to closure, so you can build branches from a list at runtime.

Construct a Map<String, Closure> (often with collectEntries) and pass it to parallel. This runs one branch per entry, which is how you fan out over a dynamic list of targets.

Steps

• Build a map of branch name to a closure of steps.
• Capture the loop variable into a local so each closure binds correctly.
• Pass the map to parallel.

Jenkinsfile

pipeline {
  agent any
  stages {
    stage('Fan out') {
      steps {
        script {
          def targets = ['us-east', 'us-west', 'eu-central']
          def branches = targets.collectEntries { t ->
            [(t): { sh "./deploy.sh --region ${t}" }]
          }
          parallel branches
        }
      }
    }
  }
}

Gotchas

• Bind the loop variable to a local inside the closure or every branch sees the last value.
• Add failFast: true to the map to stop siblings on the first failure.

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