Due to a vulnerability in VestaCP we've blocked port 8083 in hopes that this might protect you from having your server compromised and shut down completely. Droplets that were compromised were sending out DOS attacks and that required them to be taken down to keep the network online.
Using an alternate port will get you around that block, but please make sure your VestaCP is up to date. To make sure it's up to date:
apt-get update && apt-get upgrade -y
yum update -y
This one-liner will change the port from 8083 to 5600, when run via SSH or console:
sed -i 's/8083;/5600;/' /usr/local/vesta/nginx/conf/nginx.conf && v-add-firewall-rule ACCEPT 0.0.0.0/0 5600 TCP && service vesta restart
Thanks anthonyrossbach for drafting up that one-liner :)