Crash while trying to export metrics for apm-server.

[erik-bizzdo]

Hi,

I have setup beat-exporter as a sidecar to my apm-server in kubernetes but the beat-exporter crashes with the following log message:

{"level":"info","message":"Exploring target for beat type","time":"2020-11-23T17:56:52Z"}
{"beat":"apm-server","hostname":"apmserver-5668d79455-zwfp7","level":"info","message":"Target beat configuration loaded successfully!","name":"apmserver-5668d79455-zwfp7","time":"2020-11-23T17:56:53Z","uuid":"e2243c95-c7e6-47b8-8f04-b82edc41b069","version":"7.9.1"}
panic: descriptor Desc{fqName: "apm-server_up", help: "Target up", constLabels: {}, variableLabels: []} is invalid: "apm-server_up" is not a valid metric name

My guess is that apm-server reports it's name containing a dash which in turn makes beat-exporter generate a non valid Prometheus metric name.
The solution might be to convert all invalid chars in metricnames to underscores, or simply just removing them. In my case I would have been fine with either apm_server_up or apmserver_up.