Apache global configuration settings for performance

Hi i have a server with
Intel® Xeon® Processor E5-1650 v3
124gb ram
240gb ssd

centos 7.4

i need some suggestions about the global configuration settings because at default sites are down with a simple ddos i use.

the problem seems to be at Server Limit (Maximum: 20,000) and Max Request Workers .
When these options are default the sites with a ddos are down.

When i raise them seems to be ok.
But i dont know the right values