Keep-Alive or HTTP persistent connections allow the same initial server connection to send and receive multiple requests, thus reducing the lag for subsequent requests.
Header set Connection keep-alive
By default, most Apache and NGINX servers have Keep Alive enabled, however depending on your hosting provider you may have to activate it manually. ToolKit accomplishes this by adding this to your server config file:
NGINX servers have Keep Alive enabled by default unless it has explicitly been disabled in your config file. If this is the case, you’ll see the following setting in your config file and will want to update this:
Then, restart your server using the following:
$ service nginx restart
LiteSpeed servers have Keep-Alive enabled by default.
To change your server config, check out their documentation here.
Want to learn more about Keep Alive Connections?
Check out this awesome explanation on Keep Alive Connections and how it works
NGINX resource for Keep-Alive Connections