Why I can connect to my public server when its firewall is closed

[lewis617]

I ran a jamulus server on cloud, when I made it public, I could connect to it without opening the firewall(security group). why? how did it work?

plus, when I made my server private, I had to open firewall, otherwise, I couldn't connect to it.

[passing]

Directory servers do "hole punching" (https://en.wikipedia.org/wiki/Hole_punching_(networking)) for the servers connected to them.