Add nginx_up gauge

[matsumana]

I want to check the nginx is up.
so add nginx_up like a mysqld_exporter

[matsumana]

Hello.
Would you please review this?

[discordianfish]

Sorry for not spotting this earlier. Right now the scrape should fail if nginx is unreachable. You can use the up mertric for monitoring this.

[matsumana]

Thank you for your reply.

Right now the scrape should fail if nginx is unreachable. You can use the up mertric for monitoring this.

It seemed that no up metrics did not exist. so I sent this PR, is it already exists?

[discordianfish]

The up metric is provided by Prometheus itself. It's 0 if a configured target failed: https://prometheus.io/docs/concepts/jobs_instances/
Going to close this here for now. We can reopen if I missed something.

[seelensonne]

The up metric is 0 if the scrape itself fails. But if the scrape succeeds (i.e., Prometheus was able to talk to the exporter), then the nginx_up metric would tell if Nginx is up (1) or not (0).

[discordianfish]

Fair enough

[seelensonne]

Awseome! Thank you and @matsumana.

[matsumana]

Thank you, too.