Security Fixes

5 troubleshooting guides — each with the error, why it happens, and copy-paste commands to fix it.

• Docker Is Bypassing UFW — Published Ports Are Open to the World — docker run -p 5432:5432 punches through UFW by writing its own iptables rules.
• fail2ban Locked You Out of Your Own Server — fail2ban did its job — on you.
• UFW Rules Not Taking Effect — Debugging Order That Works — UFW is iptables underneath.
• SSH "Host Key Verification Failed" — Changed Keys and known_hosts — SSH refuses the connection because the host's key doesn't match what you recorded before.
• SSH "Connection Timed Out" on Port 22 — and the Firewall Chain Test — Timeout (not refused) means packets are silently dropped: firewall, security group, wrong IP, or sshd down behind a DROP policy.