Swiggy Observability, SLOs & Reliability interview questions

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.

Choose what evidence must survive, then price the collection path. A tail policy can only inspect traces that reach it; low SDK sampling changes the guarantee before the collector sees a span.

Metrics describe the server's experience; synthetics describe the user's. The strong answer designs a few money-path journeys from real geographies, pages only on persistent failure, and budgets for script rot.

Usable runbooks live one click from the alert, front-load symptom-to-action pairs, and stay alive because CI and drills force the issue rather than anyone hoping.

Rotation length decides focus versus fatigue, handoff quality decides whether Tuesday inherits Monday's mess, and follow-the-sun only works when every region holds real authority.

One surface cannot serve the responder and the review. Tier dashboards by the question each audience asks, and make every tile answer in five seconds or link one click deeper.

Sampling keeps proportions and loses rare individuals; filtering keeps chosen classes complete and loses whatever you misclassified. Decide retention at write time, keep counters always, rehydrate the rest.

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.

All three can search logs. What differs is who operates the cluster and how the bill is shaped, and the bill is what kills these projects, not the querying.

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

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.

Prometheus asks your service for numbers on a schedule rather than waiting to be told. That one design choice explains service discovery, exporters, staleness and why short-lived jobs are the awkward case.

Metrics quantify impact, traces expose instrumented request paths, and logs describe individual events. Follow a slow checkout across all three while accounting for missing evidence.

Defining chaos engineering is easy. 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.

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.

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.

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.

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.

The pull model is the famous part and explains none of the operational pain. The storage engine is where Prometheus hurts in production: crash recovery, cold queries, disk death.

Anyone can divide bad requests by total. This answer shows the aggregation mistakes that quietly corrupt SLO dashboards, the rate-versus-increase traps that make budgets lie, and when subqueries cost too much.

Dashboard sprawl is an operating-model problem wearing a tooling costume. The scored answer moves definitions into git, attaches ownership metadata to every panel, and deletes without ceremony.