After installing Centos 7, I noticed that DNS lookups for addresses saved in /etc/hosts take long time, here is example:
time curl -X get http://localhost real 0m0.159s user 0m0.004s sys 0m0.005s
time curl -X get http://127.0.0.1 real 0m0.005s user 0m0.001s sys 0m0.003s
It takes ~ 0.15 secs to resolve "localhost" by each request.
I make the same tests on another server in the same network with Centos 6.5 but "localhost" is as fast as "127.0.0.1"