Original practice scenario: A telecom simulator reports hourly cell counters, cumulative byte counts and device gauges. How would you produce a daily regional dashboard?
Read model answer +
Different measurements require different aggregation rules. Summing cumulative counters or averaging percentages without their denominators can produce plausible-looking but meaningless network statistics.
Work through it
Document each metric as a counter, interval total, gauge or ratio; detect resets and derive deltas only within valid device sessions.
Map cells to region using effective-dated assignments, then aggregate compatible intervals while tracking missing coverage and unequal sampling.
Recompute regional ratios from summed numerators and denominators, test device restarts and late reports, and reconcile against controlled synthetic totals.
Tradeoffs to discuss
Detailed raw retention supports correction but increases storage; pre-aggregates must preserve sufficient components to recompute rates.
Common pitfalls
Do not treat a counter reset as negative traffic.
An average of cell utilization percentages is not necessarily the region's capacity-weighted utilization.
Original practice scenario: A fictional service activation spans billing, subscriber records and network provisioning. One system succeeds while another times out. Design recovery behavior.
Read model answer +
Model activation as a durable workflow with observable partial states. A timeout means the outcome is uncertain, so blindly repeating every operation can create inconsistent duplicate changes.
Work through it
Give the activation and each external action stable idempotency identities, persisting intended state and acknowledgements before advancing stages.
Query uncertain outcomes where supported, retry transient failures within a budget and define compensations for reversible steps rather than assuming atomic rollback.
Test crashes between actions and acknowledgements, stale callbacks and compensation failures; expose pending recovery and manual review when automation cannot resolve state.
Tradeoffs to discuss
A saga avoids distributed locking but requires carefully defined compensations and user-visible intermediate states.
Common pitfalls
Do not mark the service active before required systems confirm.
Compensation is a new business operation, not a guarantee that history can be erased.
