AWS Elastic Beanstalk master instance nodejs cron.

aws_eb_cron.js

const logger = require('./logger'),
AWS = require('aws-sdk'),
CronJob = require('cron').CronJob;

AWS.config.update({region: 'us-east-1'}); // change to your region
var opts = {  
  credentials: new AWS.EC2MetadataCredentials()// default to use the credentials for the ec2 instance
};

var elasticbeanstalk = new AWS.ElasticBeanstalk(opts);
var ec2 = new AWS.EC2(opts);
var metadata = new AWS.MetadataService(opts);

function runTaskOnMaster(name, taskToRun) {
  logger.info('Beginning task: ' + name);

  return new Promise( (resolve, reject) => {
    metadata.request('/latest/meta-data/instance-id', (err, InstanceId) => {
      if (err) {return reject(err);}
      return resolve(InstanceId)
    });
  })
  .then((currentInstanceId) => {
    console.log('InstanceId', currentInstanceId);
    return new Promise( (resolve, reject) => {    
      var params = {
        Filters: [
          {
            Name: 'resource-id',
            Values: [currentInstanceId]
          }
        ]
      };

      ec2.describeTags(params, (err, data) => {
        if (err) {return reject('dt' + err);}

        var envIdTag = data.Tags.find(t => t.Key === 'elasticbeanstalk:environment-id');
        if (envIdTag === null) {
          return reject('Failed to find the value of "elasticbeanstalk:environment-id" tag.');
        }

        elasticbeanstalk.describeEnvironmentResources({EnvironmentId: envIdTag.Value}, function (err, data) {
          if (err) { return reject('de' + err); }
          if (currentInstanceId !== data.EnvironmentResources.Instances[0].Id) { return resolve(false); }
          return resolve(true);
        });
      });
    });
  })
  .then( (isMaster) => {
    if (!isMaster) {
      logger.warn('Not running task as not master EB instance.');
    } else {
      logger.info('Identified as master EB instance. Running task.');
      taskToRun();
    }
  })
  .catch( (err) => logger.error(err));
}

logger.info('*** Starting Cron Jobs! ***');


new CronJob('0 */5 * * * *', function() { //every 5 min
  runTaskOnMaster( 'Task 1', () => {
    //do cron work here.
  });
}, null, true);

an async/await version based on this snippet
https://gist.github.com/ayavilevich/9cea31154a71d079cb5328006a72bd53