Topic: capacity
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Capacity planning from measured headroom: usable capacity, peak demand and an exhaustion date
Measure the highest arrival rate at which the service still meets its latency objective, compare it with the real peak demand, and turn the difference into a headroom ratio and a projected exhaustion date with a scheduled action. Redundancy for failures and headroom for growth are separate budgets.
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Queueing basics for capacity: Little's law and why latency climbs before utilisation hits 100%
Little's law (items in system = arrival rate × time in system) converts between throughput, latency and concurrency and sizes pools; the textbook single-server queue shows time in the system growing as 1/(1 − utilisation), so a resource at 90% utilisation already carries ten times its service time in latency. Plan against latency, not against a full CPU.
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