Letsencrypt on Ubuntu 16.04/Nginx

I have a file digitalocean inside of that directory with the following configuration:

server {
        listen 80 default_server;
        listen [::]:80 default_server ipv6only=on;

       root /var/www/html;
        index index.php index.html index.htm;

        # Make site accessible from http://localhost/
        server_name localhost;

        location / {
                # First attempt to serve request as file, then
                # as directory, then fall back to displaying a 404.
                try_files $uri $uri/ =404;
                # Uncomment to enable naxsi on this location
                # include /etc/nginx/naxsi.rules
        }

        error_page 404 /404.html;
        error_page 500 502 503 504 /50x.html;

        location = /50x.html {
                root /usr/share/nginx/html;
        }

        location ~ \.php$ {
        include snippets/fastcgi-php.conf;
        fastcgi_pass unix:/run/php/php7.0-fpm.sock;
        }

        # deny access to .htaccess files, if Apache's document root
        # concurs with nginx's one
        #
        #location ~ /\.ht {
        #       deny all;
        #}
}

# another virtual host using mix of IP-, name-, and port-based configuration
#
#server {
#       listen 8000;
#       listen somename:8080;
#       server_name somename alias another.alias;
#       root html;
#       index index.html index.htm;
#
#       location / {
#               try_files $uri $uri/ =404;
#       }
#}


# HTTPS server
#
#server {
#       listen 443;
#       server_name localhost;
#
#       root html;
#       index index.html index.htm;
#
#       ssl on;
#       ssl_certificate cert.pem;
#       ssl_certificate_key cert.key;
#
#       ssl_session_timeout 5m;
#
#       ssl_protocols SSLv3 TLSv1 TLSv1.1 TLSv1.2;
#       ssl_ciphers "HIGH:!aNULL:!MD5 or HIGH:!aNULL:!MD5:!3DES";
#       ssl_prefer_server_ciphers on;
#
#       location / {
#               try_files $uri $uri/ =404;
#       }
#}

@chrisburton

Okay, Nginx is not listening on port 443, which likely means you have not created server block configuration for https - or you have not activated it.

Do you have a https-configuration in /etc/nginx/site-enabled ?

You are welcome to post your configuration.