Cases
Real problems from my own setup, written as: symptom → hypotheses → diagnosis → cause → fix → lessons.
Caddy in Docker, and the www certificate that wouldn't issue
Moving this site's web server into a container, then debugging why the apex got HTTPS in seconds and www kept failing.
Works from outside, fails from inside: NAT hairpin
A WireGuard server reachable over mobile data but not from the home Wi-Fi. Three days of debugging, and the answer was not a misconfiguration.
Locked out by my own firewall
Enabling ufw without an SSH allow rule. Recovery and a safe order of operations.
DHCP moved my server and took the port forward with it
Why port forwarding needs a static address or a DHCP reservation.
SSH login fails on Debian 13: where are the logs?
journalctl instead of /var/log/auth.log.