Websites down for 2 minutes but I don't know the reason


I multi time notify email from an Uptime service that my websites on a VPS are down and up again for 2 minutes.

I tried to check the reason but not sure to doing the right way.

Could you please advise me the step to check, which log files and path should check?

Thank you for your help.

Hard to say: for sure check /var/log/syslog also the related nginx and apache2 logs. beside that it could also be a network outage.