A VPS under CentOS with installed splash. Periodically, the server starts to slow down, but:
1. The processor is not loaded (involved less than one percent).
2. Memory free (over 700 meters), no swap.
3. A bunch of free nginx (as frontend) and apache (as a backend).
4. Mysql did not seem to slow down.
5. At the time the brakes have not configured any crowns.
Load average increases up to 7 and after a time gradually decreases to values less than 1. Growth occurs at any time of the day night. In these moments there are no prerequisites for the growth of loads — individual requests that another time fulfills on hurrah.
Already optimized code projects, set up opcode-caches, connected the static cache.
Sinned on neighbors in the physical server, but, first, do not believe that they can influence our LA, and secondly, the hoster says, that they have nothing to do with it (although have already been cases where our projects lay under DDoS om their sites).
In what direction to dig? What can be done?