Jenkins pipeline milestone not cancelling previous ongoing build

I don't think the behavior is "If I'm a newer build that crosses this milestone, then all older build that crossed this milestone will be cancelled"

The actual behavior of the milestone step is that when a more recent pipeline crosses it first, then it prevents older pipeline from crossing that milestone.

I have a simple work around with milestone plugin, according to the document:

• Builds pass milestones in order (taking the build number as sorter field).
• Older builds will not proceed (they are aborted) if a newer one already passed the milestone.
• When a build passes a milestone, any older build that passed the previous milestone but not this one is aborted.
• Once a build passes the milestone, it will never be aborted by a newer build that didn't pass the milestone yet.

you can try something like this:

pipeline {
    agent any
    stages {
        stage('Stop Old Build') {
            steps {
                milestone label: '', ordinal:  Integer.parseInt(env.BUILD_ID) - 1
                milestone label: '', ordinal:  Integer.parseInt(env.BUILD_ID)
            }
        }
    }
}

you can put this at the start of any pipeline.

Assume you just start a new build, #5. The first milestone, will be used to passes #4's second milestone, and the second milestone(of #5) will be used to kill #4's process, if it's currently running.

Try this:

/* This method should be added to your Jenkinsfile and called at the very beginning of the build*/
@NonCPS
def cancelPreviousBuilds() {
    def jobName = env.JOB_NAME
    def buildNumber = env.BUILD_NUMBER.toInteger()
    /* Get job name */
    def currentJob = Jenkins.instance.getItemByFullName(jobName)

    /* Iterating over the builds for specific job */
    for (def build : currentJob.builds) {
        /* If there is a build that is currently running and it's not current build */
        if (build.isBuilding() && build.number.toInteger() != buildNumber) {
            /* Than stopping it */
            build.doStop()
        }
    }
}