Distinguish resolver failure from application connection failure
Operators see one generic network error for lookup failures and refused connections.
- Focused work estimate
- 2h 30m + prerequisites
- Priority in the scenario
- Medium
- Engineering practice
- Network diagnostics
Estimated field mix
- Networking70%
- Site reliability30%
Field percentages are editorial estimates of the ticket's engineering focus. They total 100%; they are not measured time, proficiency scores, or ownership evidence.
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Project context
A fictional internal API is moving to a new endpoint. The team assumes DNS changes are immediate and has no rehearsal for stale clients.
Setup prerequisites
- Create a local resolver simulator and two loopback service endpoints with synthetic DNS records; query no external infrastructure.
Preceding work
Complete these dependencies, or supply their agreed outputs before taking this ticket.
- BDNS-101 · Inventory service records and their consumers
- BDNS-102 · Implement TTL-aware positive caching in the resolver fixture
- BDNS-104 · Reject alias loops and excessively deep resolution chains
- BDNS-103 · Model negative caching separately from empty address records
- BDNS-105 · Rehearse lowering TTL before endpoint cutover
- BDNS-106 · Preserve application compatibility across old and new addresses
Acceptance criteria
- Classify lookup, address selection, connection, and HTTP failures.
- Record bounded timing per stage.
- Keep hostnames and request data within the declared safe diagnostic policy.
Implementation constraints
- No packet payloads or credentials in generic logs.
Verification to include
- Diagnose a local nonexistent name.
- Resolve an address then distinguish refused connection.
Deliverables
- Network-stage diagnostics.
Rollout and recovery
Add classification before changing retry behavior.
Value of the work
For the engineer: Practice DNS semantics, migration timing, and network diagnosis.
For the team: Produce a migration plan that makes cache delay and endpoint compatibility explicit.
Evidence boundaries
Outcome Evidence: Tests, patches, and runbooks are requested deliverables. They become Outcome Evidence only through a qualified Mission and immutable Evidence IDs.
Ownership Evidence: Independent adaptation must be observed under a declared verification policy and cite immutable Evidence IDs. Completing a planning ticket establishes no Ownership Evidence.