J.B. Peacock
Historical technical note

When a web server would not serve to the web

A recovered troubleshooting record from the original Archives. Product names and procedures reflect the time in which it was written.

Archive note: This piece is preserved for historical interest. Cloud consoles, registrar products, and DNS interfaces may have changed since it was written.

The situation

  • A LAMP stack had been installed on a Debian 8 virtual machine.
  • Apache had been configured with virtual-host information.
  • DNS included an A record and a CNAME.
  • The site still would not resolve publicly.

Diagnosis

The site appeared to work locally, but that result was misleading. The page was cached, and the local hosts file mapped the domain directly to the server.

Tests from a different machine produced an ISP splash page or no useful address resolution. Commands such as dig example.com, nslookup example.com, and queries against a public DNS resolver pointed toward a DNS configuration problem rather than an Apache problem.

Resolution

The authoritative nameservers configured at the registrar did not match the nameservers assigned to the cloud DNS zone. Updating the registrar to use the correct cloud nameservers allowed the domain to resolve to the virtual machine.

The durable lesson

A web server can be configured correctly while the site remains unreachable. Test from outside the local machine, verify the authoritative nameservers at the registrar, and confirm that public DNS returns the intended address.