Users report a bug you cannot reproduce and that appears in no logs. How do you proceed?
What they are really testing: Whether you can investigate without the usual evidence, and whether your instinct is to improve observability rather than to dismiss the report.
A real interview question
Users report a bug you cannot reproduce and that appears in no logs. How do you proceed?
What most people say
drag me
“If it is not in the logs and I cannot reproduce it, it is probably user error.”
It dismisses a real signal and, worse, ignores the most useful clue available: the absence of a log usually means an exception is being swallowed or the failure is client-side, both of which are genuine defects in observability.
The follow-ups they ask next
What kinds of failure never reach your server logs at all?
Client-side JavaScript errors, requests failing at DNS or TLS, load balancer level rejections, timeouts where the client gave up, and CDN-served errors. Each needs its own telemetry source.
How do you find a bug that only affects one user?
Compare their state against a working user across data, permissions and flags. Single-user bugs are nearly always data-shaped: something in their records that no other account has.
What the interviewer is listening for
- Treats the missing log as a finding
- Uses timestamp and user to search successful requests
- Communicates honestly with the reporter
What sinks the answer
- Dismisses as user error
- Only searches for errors
- Closes the ticket without instrumenting
If you genuinely do not know
Say this instead of freezing. Reasoning out loud from what you do know beats silence every single time, and a good interviewer is listening for exactly that.
“No log is [a finding: a swallowed exception, a client-side failure, or an uninstrumented path]. I get [exact timestamp and account] so I can [find their actual requests and read full traces, including 200s]. Then [what differs: flags, data shape, permissions, client version]. If still invisible, [add targeted instrumentation and catch the next one], and [tell the user honestly].”
Keep going with troubleshooting
Junior
A developer says the build passes locally but fails in CI. How do you debug that?
Junior
A production server is failing writes. Disk is 100% full. Walk me through what you do.
Junior
At midnight everything started failing with TLS errors. What happened and what do you do?
Mid
A pod is in CrashLoopBackOff after a deploy. Walk me through your debugging, command by command.
Mid
The deploy reports success, pods are Running, but users get 502s. Where do you look?
Mid
A Kubernetes node goes NotReady and pods are stuck Terminating. What is happening and what do you do?
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