Port knocking works if you have to ssh to your servers, there are many solutions that obviate even that, and leave you with no open ports, but a fully manageabl

Port knocking works if you have to ssh to your servers, there are many solutions that obviate even that, and leave you with no open ports, but a fully manageable server. I'm guilty of ssm in aws, but the principal applies - the cattle phone home, you only have to call pets.