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Engineering fundamentals — the principle underneath, the tools that are just instances of it, and the buzzwords that bury it.
Append-only log
principleAn ordered, immutable sequence you only append to and read by offset. The principle under Kafka, WAL, and event sourcing — they're instances, not the idea.
Distributed lock
principleMutual exclusion across processes and servers, not threads in one JVM. The principle under ShedLock, Redlock, and SELECT FOR UPDATE.
Idempotent
principleApplying an operation N times lands in the same state as applying it once. The principle that makes retries safe — and the truth behind 'exactly-once'.
Race condition
principleCorrectness that depends on the uncontrolled interleaving of concurrent operations. The principle under lost updates, double-submits, and TOCTOU.