You haven’t specified which web server or operating system you are using so I will assume that you are running Apache on Ubuntu 14.04 or newer. If this is not the case, let me know.

The default web root for Apache on Ubuntu 12.04 was /var/www but that default has been changed in more recent releases. Current Ubuntu releases include apache with a default web root of /var/www/html If this is the case with your droplet you will need to move index.html to /var/www/html/.