Chapter 9: Domain Names, DNS and Subdomains
9.12 Troubleshooting domains
| Symptom | Likely cause | Fix |
|---|---|---|
dig returns nothing / NXDOMAIN |
Record missing, typo in name, domain not verified or expired | Check the DNS page; verify registrant email; check expiry |
dig shows old/parking IP |
Old A record still present, TTL not expired, or forwarding on | Delete the parked A record; turn off forwarding; wait for TTL; dig @8.8.8.8 |
| Records correct in GoDaddy but not used | Name servers point elsewhere (e.g. Route 53) | dig NS example.com +short; edit records where NS points |
| Domain resolves, browser times out | Security group / firewalld; wrong Elastic IP | curl -I http://EIP; open 80/443 |
| Domain shows default welcome page | server_name/ServerName doesn't include this name; default site wins |
Add the name; remove Ubuntu default; nginx -T, apachectl -S |
www works but apex doesn't (or reverse) |
Only one of the records exists, or only one name is in server_name |
Add A @ and CNAME www; list both names in config |
| Works on mobile data, not on laptop | Local DNS cache | Flush cache (section 9.9) |
| certbot: Timeout during connect / NXDOMAIN | DNS not yet pointing here, or port 80 closed | Fix DNS first; open 80; retry |
| Email stopped after moving DNS | MX/TXT records not recreated | Copy MX/TXT to the new DNS host |