code: function makePrometheus(stats, defaultLabels = {}) {
      const metricMapping = {
          processed: 'teraslice_slices_processed',
          failed: 'teraslice_slices_failed',
          queued: 'teraslice_slices_queued',
          job_duration: '', // this isn't really useful, omitting
          workers_joined: 'teraslice_workers_joined',
          workers_disconnected: 'teraslice_workers_disconnected',
          workers_reconnected: 'teraslice_workers_reconnected'
      };
  
      let returnString = '';
      _.forEach(stats.controllers, (value, key) => {
          const name = metricMapping[key];
          if (name !== '') {
              returnString += `# TYPE ${name} counter\n`;
              const labels = makePrometheusLabels(defaultLabels);
              returnString += `${name}${labels} ${value}\n`;
          }
      });
      return returnString;
  }
docs: NOTE: This only works for counters, if you're trying to extend this, you should probably switch to using prom-client.