pipeline {
    agent any
    stages {
        stage('set servers') {
            steps {
                script {
                    my_list = ['server1','server-2','server-3']
                }
            }
        }
        stage('Execute then') {
            parallel {
                stage('shouter') {
                    steps {
                        script {
                            shouter = [:]
                            script {
                                for(i in my_list) {
                                    shouter["${i}"] = {
                                        echo "standupandshout.sh ${i}"
                                    }
                                }
                            }
                            parallel shouter
                        }
                    }
                }
            }
        }
    }
}

Replayed #4
Running in Durability level: MAX_SURVIVABILITY
[Pipeline] node
Running on Jenkins in /var/lib/jenkins/workspace/test
[Pipeline] {
[Pipeline] stage
[Pipeline] { (set servers)
[Pipeline] script
[Pipeline] {
[Pipeline] }
[Pipeline] // script
[Pipeline] }
[Pipeline] // stage
[Pipeline] stage
[Pipeline] { (Execute then)
[Pipeline] parallel
[Pipeline] [shouter] { (Branch: shouter)
[Pipeline] [shouter] stage
[Pipeline] [shouter] { (shouter)
[Pipeline] [shouter] script
[Pipeline] [shouter] {
[Pipeline] [shouter] script
[Pipeline] [shouter] {
[Pipeline] [shouter] }
[Pipeline] [shouter] // script
[Pipeline] [shouter] parallel
[Pipeline] [server1] { (Branch: server1)
[Pipeline] [server-2] { (Branch: server-2)
[Pipeline] [server-3] { (Branch: server-3)
[Pipeline] [server1] echo
[server1] standupandshout.sh server-3
[Pipeline] [server1] }
[Pipeline] [server-2] echo
[server-2] standupandshout.sh server-3
[Pipeline] [server-2] }
[Pipeline] [server-3] echo
[server-3] standupandshout.sh server-3
[Pipeline] [server-3] }
[Pipeline] [shouter] // parallel
[Pipeline] [shouter] }
[Pipeline] [shouter] // script
[Pipeline] [shouter] }
[Pipeline] [shouter] // stage
[Pipeline] [shouter] }
[Pipeline] // parallel
[Pipeline] }
[Pipeline] // stage
[Pipeline] }
[Pipeline] // node
[Pipeline] End of Pipeline
Finished: SUCCESS

[Pipeline] [server1] echo
[server1] standupandshout.sh server-1
[Pipeline] [server1] }
[Pipeline] [server-2] echo
[server-2] standupandshout.sh server-2
[Pipeline] [server-2] }
[Pipeline] [server-3] echo
[server-3] standupandshout.sh server-3