Configure Let’s Encrypt for Apache on Ubuntu

sudo apt-get install python-letsencrypt-apache 

letsencrypt --apache

nano /etc/apache2/apache2.conf

<VirtualHost *:443>
	SSLEngine on
	SSLCertificateKeyFile /etc/letsencrypt/live/dl.mhdr.ir/privkey.pem
	SSLCertificateFile /etc/letsencrypt/live/dl.mhdr.ir/cert.pem
	SSLCertificateChainFile /etc/letsencrypt/live/dl.mhdr.ir/chain.pem
    DocumentRoot "/var/www/html/dl"
    ServerName dl.mhdr.ir
</VirtualHost>

service apache2 restart

PPA

$ sudo add-apt-repository ppa:certbot/certbot
$ sudo apt-get update
$ sudo apt-get install python-certbot-apache

note : only the last VitualHost will be detected by letsencrypt
References
https://certbot.eff.org/#ubuntuxenial-apache
https://www.digitalocean.com/community/tutorials/how-to-use-apache-http-server-as-reverse-proxy-using-mod_proxy-extension
https://letsencrypt.org/