code: function handleUpdate(provider, bigIp, masterIid, masterBadOrNew, options) {
          logger.info('Cluster action UPDATE');
  
          if (this.instance.isMaster && !masterBadOrNew) {
              return checkForDisconnectedDevices.call(this, bigIp);
          } else if (!this.instance.isMaster) {
              // We're not the master, make sure the master file is not on our disk
              if (fs.existsSync(MASTER_FILE_PATH)) {
                  fs.unlinkSync(MASTER_FILE_PATH);
              }
  
              // If there is a new master, join the cluster
              if (masterBadOrNew && masterIid) {
                  return joinCluster.call(this, provider, bigIp, masterIid, options);
              } else if (masterIid) {
                  // Double check that we are clustered
                  return bigIp.list('/tm/cm/trust-domain/Root')
                      .then((response) => {
                          if (!response || response.status === 'standalone') {
                              logger.info('This instance is not in cluster. Requesting join.');
                              return joinCluster.call(this, provider, bigIp, masterIid, options);
                          }
                          return q();
                      })
                      .catch((err) => {
                          throw err;
                      });
              }
          }
          return q();
      }
docs: Handles --cluster-action update
  
  Called with this bound to the caller