In the apache2 logs there are errors File does not exist... referer from other sites, what could it be?

Question

Apache HTTP Server

Recently, the site began to literally fail for 20-30 minutes, despite the fact that there is still 2gb of free memory, 30gb of disk space.
All that I found in the logs at the moments of failures was accessing non-existent request folders on my server with completely left referrers from strangers, unfamiliar me sites. Naturally, the flow of these requests is frightening. 200-300 per minute.
What could it be? Under-ddos? Or my curvature? How can you filter this crap?

[Tue Jan 27 08:04:31 2015] [error] [client 58.57.50.74] File does not exist: /var/www/domain.ru/public_html/fs16, referer: http://www.tzhqw.com/vso-97%E8%9C%9C%E6%A1%83%E5%9B%BE%E7%89%87ccc36.html
[Tue Jan 27 08:04:34 2015] [error] [client 171.83.85.30] File does not exist: /var/www/domain.ru/public_html/14430, referer: http://armorgames.com/
[Tue Jan 27 08:04:42 2015] [error] [client 171.83.85.30] File does not exist: /var/www/domain.ru/public_html/10317, referer: http://armorgames.com/
[Tue Jan 27 08:04:42 2015] [error] [client 171.83.85.30] File does not exist: /var/www/domain.ru/public_html/4071, referer: http://armorgames.com/
[Tue Jan 27 08:04:46 2015] [error] [client 171.83.85.30] File does not exist: /var/www/domain.ru/public_html/6106, referer: http://armorgames.com/
[Tue Jan 27 08:04:47 2015] [error] [client 117.135.35.94] File does not exist: /var/www/domain.ru/public_html/fotomen.cn, referer: http://fotomen.cn/2015/01/martin-pfister/?from=timeline&isappinstalled=0
[Tue Jan 27 08:04:47 2015] [error] [client 117.135.35.94] File does not exist: /var/www/domain.ru/public_html/fotomen.cn, referer: http://fotomen.cn/2015/01/martin-pfister/?from=timeline&isappinstalled=0
[Tue Jan 27 08:12:58 2015] [error] [client 49.77.98.163] File does not exist: /var/www/domain.ru/public_html/images/common, referer: http://alt.com/p/register.cgi
[Tue Jan 27 08:12:58 2015] [error] [client 49.77.98.163] File does not exist: /var/www/domain.ru/public_html/images/js, referer: http://alt.com/p/register.cgi
[Tue Jan 27 08:12:58 2015] [error] [client 49.77.98.163] File does not exist: /usr/share/javascript/live_cd, referer: http://alt.com/p/register.cgi
[Tue Jan 27 08:12:58 2015] [error] [client 49.77.98.163] File does not exist: /usr/share/javascript/live_cd, referer: http://alt.com/p/register.cgi
[Tue Jan 27 08:13:39 2015] [error] [client 49.77.98.163] File does not exist: /var/www/domain.ru/public_html/images/bdsm, referer: http://banners.alt.com/go/page/115385_02?pid=g1180758-pct&no_click=1&popunder_off=1
[Tue Jan 27 08:13:41 2015] [error] [client 49.77.98.163] File does not exist: /var/www/domain.ru/public_html/bdsm, referer: http://banners.alt.com/go/page/115385_02?pid=g1180758-pct&no_click=1&popunder_off=1
[Tue Jan 27 08:13:49 2015] [error] [client 117.136.75.151] File does not exist: /var/www/domain.ru/public_html/c, referer: http://www.weather.com/wx/today/?lat=26.07&lon=119.30&par=apple_widget&locale=zh_CN
[Tue Jan 27 08:13:51 2015] [error] [client 124.95.131.6] File does not exist: /var/www/domain.ru/public_html/c, referer: http://www.weather.com/weather/today/l/CHXX0119:1:CH
[Tue Jan 27 08:13:56 2015] [error] [client 119.63.196.124] File does not exist: /var/www/domain.ru/public_html/image/DbLiteGraphic
[Tue Jan 27 08:13:57 2015] [error] [client 211.140.239.200] File does not exist: /var/www/domain.ru/public_html/c, referer: http://ads.pubmatic.com/AdServer/js/showad.js
[Tue Jan 27 08:13:59 2015] [error] [client 119.63.196.123] File does not exist: /var/www/domain.ru/public_html/image/DbLiteGraphic
[Tue Jan 27 08:14:06 2015] [error] [client 124.95.131.6] File does not exist: /var/www/domain.ru/public_html/c, referer: http://www.weather.com/weather/today/l/CHXX2476:1:CH

Answer 1

Get used to it - this will happen all the time, bots look for open ftp and then check the availability of files on the site.