Netflix Observability, SLOs & Reliability interview questions

The arithmetic takes ten seconds and most candidates stall on it. The stall is the signal: it means error budgets are something you have read about rather than used.

Every candidate can define chaos engineering. Far fewer can say what they would break first, and almost none volunteer the abort condition, which is the thing that makes it a programme rather than an incident.

Alert fatigue is a design failure, not a discipline failure. The fix is a rule about what may page at all, and burn-rate alerting is how you implement it.

The roles question is really a delegation test: can you split commanding the incident from fixing it? Name the roles, the comms cadence, and the handoff discipline that keeps 3am coherent.

The kernel watches syscalls, sockets and short-lived processes that userspace agents polling every few seconds never meet. Know what eBPF adds, what it costs, and the security conversation it starts.

Facilitation is mechanics: timeline before theories, blame converted into system questions, actions with owners tracked to closure. Include the defensive engineer and the exec who wants a head.

Where linear models break: compounding growth, step functions, peak days and saturation cliffs. Forecast per constrained resource, backtest, subtract lead time to get the real order-by date.

Detectors earn their keep on seasonal aggregates and fleets of similar series, run in shadow mode with measured precision. They lie on low-volume series, bursty workloads and regime changes.

MTTR is three clocks hiding in one number. Profile detection, diagnosis and fix separately from incident timestamps; attack whichever clock dominates, which is almost never rollback speed.

Their green page, your red SLO. Separate their true failure rate from the amplification your own client adds, buffer at the boundary, then escalate with a client-side scorecard instead of feelings.

Tracing tells you which service and which span. It stops at the function boundary, and that is exactly where a CPU regression lives. Continuous profiling is the layer most teams do not have when they need it.

There is no status code and no caller waiting, so latency and error rate stop meaning what they meant. The signals that replace them are age, lag and completion, and they answer a question the request-response set never had to ask.

HTTP success can carry a rejected-span count. Replaying that batch can duplicate accepted telemetry, while enlarging the queue cannot repair invalid data.

The observability failure that scales with your success. Cardinality is the cost driver in every metrics system, and the fix has to be structural or it comes back next quarter.

A question with a right answer and a subtle reason. Histogram versus summary is the part that catches people, and it turns on whether you can aggregate across instances.

Tracing is the only telemetry that answers where the time went across services. The mechanism is context propagation, and the reason teams fail at it is that one uninstrumented hop breaks the chain.

The instinct is to delete old logs. That is backwards: the waste lives in what you ingest, not how long you keep it. This answer walks the levers in the order that actually pays.

OpenTelemetry is an API and a wire protocol, not a product. Candidates who promise instant multi-vendor bliss have never run the collector in production or negotiated with a vendor who knows it.

Day-one telemetry is cheap and retrofitting it costs an incident. The answer that scores names the linking layer (trace IDs in logs, exemplars on metrics) that turns three tools into one story.