I've never used the cluster code, @zbjornson?

Is there a way to aggregate clusterMetrics() result with default register.metrics

metricsServer.get('/metrics', (req, res) => {
    aggregatorRegistry.clusterMetrics()
    .then(metrics => {
      res.set('Content-Type', aggregatorRegistry.contentType)
      // How to merge 'metrics' with register.metrics ?
      res.send(metrics))
    })
    .catch(err => {
      error(err)
      return res.status(500).end(err)
    })
  })

@miton18 Since the Prometheus metrics format is plain text, I think that you can just concatenate the string from aggregatorRegistry.clusterMetrics() with the string from masterRegistry.metrics(). From your example (untested):

metricsServer.get('/metrics', (req, res) => {
    aggregatorRegistry.clusterMetrics()
    .then(metrics => {
      res.set('Content-Type', aggregatorRegistry.contentType)
      metrics += otherRegistry.metrics(); // <-- added
      res.send(metrics))
    })
    .catch(err => {
      error(err)
      return res.status(500).end(err)
    })
  })

Yes we can... and it's works ;-)

But I asking if it wasn't interesting to natively add Master metrics with workers ones ?

Ah, probably! Happy to review a PR for that.

I think that you can just concatenate the string from aggregatorRegistry.clusterMetrics() with the string from masterRegistry.metrics().

This will only work if there is no overlap between the metrics, otherwise you could end up with invalid output.

There are any updates? It would be nice to have #280 merged

#280 just need tests. If anyone here can contribute a test, we can get that PR landed!