Troubleshooting
Diagnostic workflow before changing configuration.
Start with the correct layer. Avoid random fixes before knowing whether the failure is in the process, local firewall, provider firewall, DNS, or application.
Recommended order
Local stateRun
fgwcp doctorand confirm services.ListenersUse
ss -lntupto confirm that the port is actually open in the process.Local firewallReview UFW and the effective iptables order.
Cloud firewallReview the cloud firewall, inbound rules, or network ACL.
Authoritative DNSQuery the nameserver IP directly with
dig @IP.Public DNSQuery 1.1.1.1 and 8.8.8.8.
ApplicationOnly then investigate the site runtime, logs, and dependencies.
Minimum toolkit
Terminal
fgwcp doctor ss -lntup ufw status verbose iptables -S INPUT dig @1.1.1.1 example.com A curl -I https://example.com