Empty requests in Apache logs during ddos, is there a method to deal with this?

Question

Nginx

good evening friends, I encountered such a problem, a bunch of empty get requests with an unknown browser appear in the logs of the virtual server.

*.*.*.* - - [08/Mar/2015:18:25:30 +0300] "GET / HTTP/1.0" 200 44059 "-" "-"
*.*.*.* - - [08 /Mar/2015:18:25:30 +0300] "GET / HTTP/1.1" 200 44112 "-" "-"
*.*.*.* - - [08/Mar/2015:18:25:30 + 0300] "GET / HTTP/1.0" 200 44059 "-" "-"
*.*.*.* - - [08/Mar/2015:18:25:30 +0300] "GET / HTTP/1.0" 200 44512 "-" "-"
*.*.*.* - - [08/Mar/2015:18:25:30 +0300] "GET / HTTP/1.0" 200 44059 "-" "-"
*.*.* .* - - [08/Mar/2015:18:25:30 +0300] "GET / HTTP/1.1" 200 44096 "-" "-"

Joomla netbot attack method, How to deal with it? because with so many requests, the server feels very bad.

Answer 1

a) cache the main page
b) filter requests to nginx with an empty user-agent

Answer 2

And how to filter them out on nginx?
So I understand?
if ($http_user_agent ~* msnbot|scrapbot|Browser|ms_ie|-) {
return 403;
}