Autoscaling & Health
Horizontal, vertical, scheduled and metric-based scaling; choosing the signal that represents workload pressure rather than the one that is easiest to read; startup time as the reason scaling lags; and health checks — including the liveness/readiness confusion that turns a deploy into an outage.
Capacity that follows demand instead of a human. Horizontal, vertical, scheduled and metric-based scaling, what each one actually changes — and why every one of them reacts to load that has already arrived.
Q · How does the amount of capacity running follow the amount of demand arriving, without a human watching a graph?
Scale on the signal that represents workload pressure. CPU is the default and it is frequently the wrong answer — an I/O-bound service saturates its connection pool at 30% CPU while the scaler reports everything is fine.
Q · Which measurement should decide how much capacity is running — and why is the easiest one to read usually the wrong one?
New capacity does not appear when you ask for it. Decompose the delay — metric window, decision, provisioning, image pull, runtime boot, warm-up, health check — and the reason autoscaling always looks late stops being mysterious.
Q · Why does capacity requested now start serving traffic minutes from now, and which part of that delay can I actually shorten?
The mechanism that decides which instances receive traffic. A check that only proves the web framework is running proves nothing; a check that verifies every dependency turns one slow dependency into a total outage.
Q · How does the load balancer decide which instances are allowed to receive requests, and what should that check actually verify?
Two probes answering two different questions. Liveness asks whether the process is alive enough to continue; readiness asks whether it can serve traffic right now. Confusing them turns a database blip into a fleet-wide crash loop.
Q · What is the difference between "restart this process" and "stop sending it traffic", and why does confusing them cause outages?