how to reduce the Requests on apache2 server ?

If you have IP address of bot accessing your site, you can block it using firewall or Apache config.

A firewall blocking is easier IMO, as one command will block IP to accessing your server. On Ubuntu, you can use ufw which is very simply to configure and use. Step 7 of Initial Server Set Up tutorial covers setting up a ufw firewall. To block IP address, you can use following command:

sudo ufw deny from 15.15.15.51

Where 15.15.15.51 is IP address of user/bot you want to block. Also, you can block subnet following command:

sudo ufw deny from 15.15.15.0/24

ufw essential tutorial should give you more insight on this topic.

Second option is to block via Apache config. This could be harder, as you have to change config and restart/reload Apache every time you do so. Apache docs should help you around this if you’re interested in it.

Be very careful when you doing above. You can sometimes block regular users or ‘good’ bot. For example, Google uses bots to crawl and index your web site. If you block Google bot, this will affect your rank in Google Index and position on Google Search. In case of Google, you can verify are bots accessing your site their, by following steps written on their help page. Same applies for other engines, so make sure you really ban malicious bots.