What's the logic of checking if server is up

[Roy Zhang]

Dear JVM exporter experts,

I am using prometheus to collect JVM exporter metrics and visualize with Grafana. But there is no data in Grafana (and there is no data in prometheus as well).
When there is no data, Grafana show the server is down. But I use prometheus to wget /metrics of that server successfully.
So I am a bit confused, what's the logic of checking if the server is up?
Really appreciate ur great help in advance!

Thanks,
Roy

[Roy Zhang]

Update title a little bit.