How do I setup firewall to block all access from outside

You can use iptables/ipset to restrict access to the mysql port (3060):

• https://www.hostinger.com/tutorials/iptables-tutorial

• https://phoenixnap.com/kb/iptables-tutorial-linux-firewall

• https://www.tutorialspoint.com/unix_commands/iptables.htm

• https://malware.expert/howto/ipset-with-iptables/

-- sw

localhost is the "loopback address": 127.0.0.1 and ::1. It should always be open. Very bad things can happen if you disable them.

Traffic to/from localhost is local to your Linode only and is never routed outside it.

-- sw

I would still like the app to be accessible to anyone but the db would have no outside access except for a few ips.
Only the App and the few ips can access the db.