Often in DevOps-minded organizations, promoting update sets from lower instances to the Production Environment is considered as something to be automated. As there is no such OOB facility available in ServiceNow, the following script is built to fulfill this requirement.

Recommended Algorithm

Supportive Scripts

1. Get Completed Updatesets from Remote instance

//get completed updatesets from a remote instance
function getCompletedUpdateSetsFromRemote(instance_name){
    //get data source
    var id, gr   = new GlideRecord('sys_update_set_source');
    gr.addQuery('name',instance_name);//name of the target environment
    gr.query();
    if(gr.next()){
        id= gr.getUniqueValue();
    }
    //define worker and required paras
    var worker = new GlideUpdateSetWorker();
    var sys_id = id;
    //initiate worker
    worker.setUpdateSourceSysId(sys_id);
    worker.setBackground(true);
    worker.start();
    //start an one time schedule
    var progress_id = worker.getProgressID();
}

2. Auto Preview UpdateSets

//OPTIONAL if you have auto preview enabled
//Auto preview loaded update sets which has a specific prefix
function AutoPreviewUpdateSets(update_set_prefix){
   //Query the remote update sets
   var remote_updateset = new GlideRecord('sys_remote_update_set');
   remote_updateset.addQuery('sys_class_name=sys_remote_update_set^nameSTARTSWITH'+update_set_prefix);
   remote_updateset.query();
    while(remote_updateset.next()){
        if(!remote_updateset.sys_id.nil()) {
            //update state of selected update sets to preview
            if(remote_updateset.state == 'loaded'){ //eliminate invalid status
                remote_updateset.state = "previewed";
                remote_updateset.update();
                // run previwer job
                var t = new UpdateSetPreviewer();
                t.removePreviewRecords(remote_updateset.sys_id);
                t.generatePreviewRecords(remote_updateset.sys_id);
            }
        }
    }

}

3. Commit Remote UpdateSets

//Commit previewed updates which has a specific prefix
function commitRemoteUpdateSets(update_set_prefix){
    var remote_updateset = new GlideRecord('sys_remote_update_set');
    remote_updateset.addQuery('sys_class_name=sys_remote_update_set^nameSTARTSWITH'+update_set_prefix);
    remote_updateset.query();
     while(remote_updateset.next()){
        if(!remote_updateset.sys_id.nil() && remote_updateset.state == 'previewed') {
            //check updateset issues are fixed
            if(!GlidePreviewProblemHandler.hasUnresolvedProblems(remote_updateset.sys_id)) 
            {
            var sys_up_set = new GlideRecord('sys_update_set');
            var worker = new GlideUpdateSetWorker();
            var local_sys_id = worker.remoteUpdateSetCommit(sys_up_set, remote_updateset, remote_updateset.update_source.url);
            var xml_gr = new GlideRecord("sys_update_xml");
            xml_gr.addQuery("remote_update_set", remote_updateset.sys_id);
            xml_gr.query();
            //execute commit and XML installtion
            while(xml_gr.next()) 
            {
                    var local_xml_gr = new GlideRecord("sys_update_xml");
                    local_xml_gr.initialize();
                    local_xml_gr.name = xml_gr.name;
                    local_xml_gr.payload = xml_gr.payload;
                    local_xml_gr.action = xml_gr.action;
                    local_xml_gr.type = xml_gr.type;
                    local_xml_gr.target_name = xml_gr.target_name;
                    local_xml_gr.view = xml_gr.view;
                    local_xml_gr.update_domain = xml_gr.update_domain;
                    local_xml_gr.table = xml_gr.table;
                    local_xml_gr.category = xml_gr.category;
                    local_xml_gr.application = xml_gr.application;
                    local_xml_gr.update_set = local_sys_id;
                    if (local_xml_gr.isValidField('replace_on_upgrade'))
                    local_xml_gr.replace_on_upgrade = xml_gr.replace_on_upgrade;
                    local_xml_gr.insert();
            }
            remote_updateset.update();
            }

        }
     }
}

4. Create New Updateset

The credit of creating this script goes to @Keminda

//Create updateset and make it current
function createUpdateSetAndMakeCurrent(update_set_name)
{
    var up= new GlideRecord("sys_update_set");
    up.initialize();
    up.application ='global';
    up.name = update_set_name;
    up.description = 'Onboarding Catalog Item';
    var updateset_sys_id= up.insert();
    //Make updateset current
    var upset= new GlideUpdateSet();
    upset.set(updateset_sys_id);
}