Insights
How we build, written down.
Notes from the team on shipping and running software. Practice, not theory.
There is no exactly-once delivery, only idempotency
Kafka's exactly-once semantics are real, and they end at the edge of Kafka. Past that boundary, the only workable answer to a retry is a key the receiver recognizes.
Holding a sub-100ms latency budget for two years
Hitting a latency target on launch day is easy. Holding it means writing the budget down as an allocation, measuring the tail, and letting a regression fail the build.
Reconciliation is a control, not a nightly report
Counting differences is not reconciliation. Classifying them, owning them, and being able to name the missing event is - and that is the real argument for an event log.
How we cut over a system that is not allowed to stop
Big-bang weekends work until the one time they do not. The alternative is dull on purpose - a reconciled backfill, one owner of truth, and traffic moved a slice at a time.
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