We provide hosting services (Dedicated Server) to a client whose website is based on drupal. This month, his website goes offline for 15 minutes every 2 days.
We already have monitoring tools (i.e pinguzo) showing that the server never went down. And the log files show nothing that is related to this issue. Also, there is no crontab entry executing every 2 days.
And we already checked the website many times at the same hour, but we never encountered the website while offline.
Nevertheless, the client still sends reports about this issue, and we do not know what could be the culprit.
Where should I look? Is there anything in drupal that can cause this?