Apache error log - server overloaded?

Question

maybe some expert can help me with this problem: I am getting the following error on the Apache log, this happens mostly when traffic is high and every one-two minutes but the rest of the day it happens every 5-10 minutes too. I have a 32 cores server with 128gb ram, using mpm event Apache 2.4 with keepalive on and maxclients 3000. This is only for Apache, I am connecting to a remote MySQL dedicated server.

[Wed May 18 09:04:23.304162 2016] [core:error] [pid 14427:tid 109067598780160] [client 223.227.170.67:15501] AH00524: Handler for (null) returned invalid result code 70007, referer: https:$
[Wed May 18 09:08:48.716167 2016] [core:error] [pid 23012:tid 109067562034944] [client 103.246.201.7:20716] AH00524: Handler for (null) returned invalid result code 70007, referer: https:/$
[Wed May 18 09:11:33.056162 2016] [core:error] [pid 11230:tid 109067733079808] [client 103.246.201.58:16297] AH00524: Handler for (null) returned invalid result code 70007, referer: https:$
[Wed May 18 09:12:19.544211 2016] [core:error] [pid 16838:tid 109067831011072] [client 103.246.200.28:47581] AH00524: Handler for (null) returned invalid result code 70007, referer: https:$
[Wed May 18 09:13:27.176166 2016] [core:error] [pid 14427:tid 109067831084800] [client 103.246.201.25:32601] AH00524: Handler for (null) returned invalid result code 70007, referer: https:$
[Wed May 18 09:14:38.224143 2016] [core:error] [pid 11230:tid 109067697231616] [client 223.227.170.67:15410] AH00524: Handler for (null) returned invalid result code 70007, referer: https:$
[Wed May 18 09:15:21.600233 2016] [core:error] [pid 14427:tid 109067705698048] [client 103.246.200.31:60991] AH00524: Handler for (null) returned invalid result code 70007, referer: https:$
[Wed May 18 09:16:42.652179 2016] [core:error] [pid 9205:tid 109067659392768] [client 103.246.201.37:14295] AH00524: Handler for (null) returned invalid result code 70007, referer: https:/$
[Wed May 18 09:19:06.356158 2016] [core:error] [pid 9205:tid 109067740841728] [client 103.246.201.4:21377] AH00524: Handler for (null) returned invalid result code 70007, referer: https://$
[Wed May 18 09:19:10.388161 2016] [core:error] [pid 11230:tid 109067705874176] [client 103.246.200.5:29111] AH00524: Handler for (null) returned invalid result code 70007, referer: https:/$
[Wed May 18 09:27:51.292172 2016] [core:error] [pid 11230:tid 109067598817024] [client 103.246.200.37:31527] AH00524: Handler for (null) returned invalid result code 70007, referer: https:$
[Wed May 18 09:29:15.904172 2016] [core:error] [pid 23917:tid 109067616036608] [client 103.246.201.44:41459] AH00524: Handler for (null) returned invalid result code 70007, referer: https:$

The 'referer' is not just one file, it seems it's happening randomly on any page of my website. I don't think I have a lot of traffic to think that the server is overloaded, but I can't find a way to fix this. Any idea about where to start searching for this problem? Thanks in advance.

Answer 1

MaxClients is unreasonably high. Lower it to, say, 100. If you need more scaling, add more machines, plus a load balancer in front of them. And use "round-robin".