server2

<VirtualHost *:80>
        ServerAdmin webmaster@localhost
        ServerName sub.example.com

      <Proxy *>
       Require all granted
      </Proxy>

      ProxyPass "/" "http://10.0.0.30/"
      ProxyPassReverse "/" "http://10.0.0.30/"

RewriteEngine on
RewriteCond %{SERVER_NAME} =sub.example.com
RewriteRule ^ https://%{SERVER_NAME}%{REQUEST_URI} [END,NE,R=permanent]
</VirtualHost>
<IfModule mod_ssl.c>
<VirtualHost *:443>
        ServerAdmin webmaster@localhost
        ServerName sub.example.com
        SSLEngine on

      <Proxy *>
       Require all granted
      </Proxy>

      ProxyPass "/" "http://10.0.0.30/"
      ProxyPassReverse "/" "http://10.0.0.30/"

    Include /etc/letsencrypt/options-ssl-apache.conf
    SSLCertificateFile /etc/letsencrypt/live/sub.example.com/fullchain.pem
    SSLCertificateKeyFile /etc/letsencrypt/live/sub.example.com/privkey.pem
</VirtualHost>
</IfModule>