Local DNS Failure Can Look Like a Dead Server

Test the known address before rebooting a host just because its name stopped resolving.

I keep this as a field note because the failure mode is easy to misclassify: name resolution failure is mistaken for host or service failure. The useful move is to identify the boundary first, then change only the layer that owns it.

What I model

The system is easier to debug when intent, observation and transport are not collapsed into one state. For this case, my rule is simple: Test the address path before declaring the host down.

Implementation pattern

Probe resolution, route, transport and application response as separate contracts.

I prefer a small explicit contract over a clever implicit one. That gives logs, tests and dashboards something concrete to verify and keeps unrelated layers from compensating for each other.

What I verify

• known address can be tested directly
• DNS differs from TCP failure
• service health is checked after reachability

Failure handling

When one of those checks fails, I preserve the failing evidence before restarting or changing configuration. The first broken contract determines the next investigation. That keeps troubleshooting causal instead of turning it into a sequence of guesses.

What I keep

Test the address path before declaring the host down. The specific tools can change, but that ownership boundary remains useful across firmware, networks and infrastructure.