DNS cache ignores TTL Debugging Lab

DNS cache ignores TTLNetwork & ConnectivityMediumPreparing workspaceAutosaved

00:00

Incident Dossier

DNS cache ignores TTL

After a maintenance window rotates the IP behind `db.internal`, the service keeps dialing the old address for hours. The upstream DNS resolver hands out a fresh record with a short TTL, but the in-process cache believes its first answer forever. Recovery requires a full restart of every worker.

Initial failing signalDNS lookup never refreshes after TTL elapsesExpected second lookup after TTL returns the new IP · received second lookup returns the cached old IP

Progress

1Reproduce the bugRun checks

2Edit the fixOpen

3Pass checksOpen

4Submit fixOpen

Reproduction Steps

Run npm test.
Inspect the failing assertion: a hostname whose resolver rotates the IP is still returning the cached answer.
Trace how createDnsCache stores and reads entries.
Track an expiresAt timestamp alongside each cached record and refresh on expiry.

Focus Mode

Start

src/dns.js

Likely area

src/dns.js

Progressive hints

Hints reveal broad direction first, then narrow toward the suspect path without showing hidden tests or exact solution code.

TopicNetwork & Connectivity

DifficultyMedium

Est. time18 min

Workspacecreating

Explorer

Preparing workspace files…

Evidence Map

Failing signal loaded from challenge API
Workspace files loaded from workspace API
Results rendered only after API run/submit

Autosaved

workspace

Outputread-onlyready$ workspace boot

Workspace booting...