* scrape: Add global jitter for HA server
Covers issue in https://github.com/prometheus/prometheus/pull/4926#issuecomment-449039848
where the HA setup become a problem for targets unable to be scraped simultaneously.
The new jitter per server relies on the hostname and external labels which necessarily to be uniq.
As before, scrape offset will be calculated with regard the absolute time, so even
restart/reload doesn't change scrape time per scrape target + prometheus instance.
Use fqdn if possible, otherwise fall back to the hostname. It adds extra random seed
to calculate server hash to be distinguish on machines with the same hostname, but
different DC.
Signed-off-by: Aleksei Semiglazov <xjewer@gmail.com>
Although it is spelling mistakes, it might make an affects
while reading.
Co-Authored-By: Kim Bao Long longkb@vn.fujitsu.com
Signed-off-by: Nguyen Hai Truong <truongnh@vn.fujitsu.com>