Github user zentol commented on the issue:
https://github.com/apache/flink/pull/4586
And this fails as well:
```
public static void main(String[] args) throws IOException {
PrometheusReporter p1 = new PrometheusReporter();
PrometheusReporter p2 = new PrometheusReporter();
MetricConfig mc = new MetricConfig();
mc.put("port", "9001");
p1.open(mc);
p2.open(mc);
}
```---
