I have my app (WordPress) and database (MySQL) on separate servers; they are connected on a private network provided by the hosting service provider, and I've taken all the preliminary steps (that I know of) for security.
Normally, I go with these IPTables rules:
*filter # Allow all loopback (lo0) traffic and drop all traffic to 127/8 that doesn't use lo0 -A INPUT -i lo -j ACCEPT -A INPUT -d 127.0.0.0/8 -j REJECT # Accept all established inbound connections -A INPUT -m state --state ESTABLISHED,RELATED -j ACCEPT # Allow all outbound traffic - you can modify this to only allow certain traffic -A OUTPUT -j ACCEPT # Allow HTTP and HTTPS connections from anywhere (the normal ports for websites and SSL). -A INPUT -p tcp --dport 80 -j ACCEPT -A INPUT -p tcp --dport 443 -j ACCEPT # Allow SSH connections # # The -dport number should be the same port number you set in sshd_config # -A INPUT -p tcp -m state --state NEW --dport 22 -j ACCEPT # Allow ping -A INPUT -p icmp -j ACCEPT # Log iptables denied calls -A INPUT -m limit --limit 5/min -j LOG --log-prefix "iptables denied: " --log-level 7 # Drop all other inbound - default deny unless explicitly allowed policy -A INPUT -j DROP -A FORWARD -j DROP COMMIT
But for my standalone (MySQL) database server, I see that the rules need some changes. For example, I need to open port 3306 for MySQL, which would be as simple as:
-A INPUT -p tcp --dport 443 -j ACCEPT
Except, I don't know how to modify it so that only the app server is able to connect to the database (i.e. so that it supports a remote connection). So, how do I do it?