Stateless Service
Cache in the instance, keep truth outside it. The difference decides whether a restart is routine or an incident.
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COST Metric
A system that scales beautifully may still be slower than one thread. COST names the hardware a platform needs before it beats a good single-threaded program.
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Quality Attributes and Trade-offs
Fast, reliable, and scalable mean different things to different teams. Define each quality precisely, measure it, and see where improving one costs another.