Is there any way where I can add custom metric to Prometheus? I would like to have an alert when upstream is down.
This is not possible out of the box as of today.
You can take the existing Promethus plugin and modify it to include these metrics.
This would also be a nice addition to the plugin so please feel free to PR it as well!
Does EE vitals/statsd metrics include this metric?
Kong Vitals includes some visibility into latency of the upstream but I don’t think it has metrics around (un)healthiness of targets of Upstreams (yet).