Telegraf daemon not receiving metrics from app deployed with Dokku

I've already monitored NodeJS apps in the past with Telegraf+InfluxDB+Grafana, but it's the first time I try to monitor a Dokku app, without success so far.

I have the following setup

app server                                          monitoring serveur
- telegraf daemon (listening on udp 8125)   ------> InfluxDB + Grafana
- dokku
  - myapp : sending metrics on localhost:udp:8125

I have the issue that metrics sent from myapp on udp://localhost:8125 are not received by telegraf.

The connectivity from telegraf to influxdb and grafana is ok, because I ran the following command on the app server:

echo "foobar:1|c" | nc -u -w0 127.0.0.1 8125

And I could visualize inside Grafana the foobar counter increment.

So I'm guessing the issue is due to myapp or how I configured Dokku.

In myapp (a node JS app), I'm using the hot-shots package to send metrics (also tried with lynx without success).

This is the code I use to instanciate the statsd client.

var StatsD = require('hot-shots');
var client = new StatsD();
// Attaching an error handler to client's socket
client.socket.on('error', function(error) {
  console.error('StatsD client error in socket: ', error);
});

I increment a counter on app startup to signal a restart. This is done with the following code:

metrics.increment('server_restart', function(err, bytes) {
  if (err) {
    console.log(err);
  } else {
    console.log('StatsD sent : ', bytes);
  }
});

Inside the app server, I ran dokku logs myapp after performing a deployment.

I get the following output

$ dokku logs myapp
2017-05-06T14:51:19.977938845Z app[web.1]:
2017-05-06T14:51:19.977996938Z app[web.1]: > myapp@1.0.0 start /app
2017-05-06T14:51:19.978002950Z app[web.1]: > node .
2017-05-06T14:51:19.978005766Z app[web.1]:
2017-05-06T14:51:21.849086537Z app[web.1]: StatsD sent :  18
$

So it seems that the metrics payload is properly sent on the right port, but it never reaches telegraf.

• Is there any configuration to do in Dokku to authorize external UDP requests to localhost ?
• What can I do to debug this further ?

via Overdrivr