Instructor answer key

Answer key and reasoning

1. Yes. An aggregate can hide a hot core, lock, queue, quota or dependency. Saturation is queued or refused work at a limiting resource, not a universal utilization threshold.
2. It chooses an earlier, legible failure. A bound can reject or expire work before physical memory, connections or latency collapse unpredictably.
3. Scaling created new provisioning and connection demand. The response was locally rational yet coupled to other finite services.
4. Log amplification. Error volume may consume CPU, allocations, threads, I/O, bytes or inodes and deepen the incident.
5. Restart resets the evidence. If each deploy clears retained resources, the leak appears as a long-horizon trend or only during an unusually long interval.
6. Recognition, authority, expertise and feedback. Someone must know when and how to use the flag, have access, and observe whether it helped.
7. Unknown boundaries require evidence. The point is not to welcome harm; it is that small contained surprises and vicarious learning reveal brittleness that design alone misses.
8. Sensemaking. Preserve signals, hypotheses, discarded explanations, coordination constraints, improvisations and what responders needed but lacked.

Exercise B guidance

• Pool headroom primarily expands the base envelope.
• An expiring traffic block creates optionality; using it well activates adaptive capacity.
• Isolation expertise turns a control into adaptive capacity.
• A reasoning-rich postmortem develops future expertise and therefore potential adaptive capacity.

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