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The Loop That Pays For It

Demand to warm pools to oversubscription to hibernation to reclaim, and back.

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Observe demand starts by pair Size warm pools ≤ 7% of spend Admit or shed class-aware Place on oversubscribed hosts 4:1 memory Detect idleness composite signal Hibernate and tier $0.004/h Reclaim and archive 30 → 90 d Fleet economics forecast capacity placement pressure relief storage headroom The Loop That Pays For It Application we own Decision point Data store Oversubscription is only safe because hibernation is the relief valve; break the idleness signal and the ring stops closing. v 1.0 · owner Platform Architecture · date 2026-10

Decisions

  • Oversubscription is a tuned parameter with hibernation as its relief valve, not an accident of scheduling (ADR-11).
  • Warm pools are sized from observed demand per (prebuild, machine class, region) and capped as a declared fraction of fleet spend, so the fast-start feature cannot quietly eat the margin.
  • Reclamation archives rather than deletes, after notifying the owner — the loop closes on storage, not on lost work.

Assumptions

  • 4:1 memory oversubscription at the nominal class; ≤ $0.085 per active workspace-hour all-in and ≤ $0.004 hibernated.
  • Spend ceilings are enforced at admission, per tenant and per principal.

Risks

  • Every arrow in this ring depends on the idleness signal being right; break it and oversubscription becomes an availability incident within one working day.
  • A warm pool is pre-paid capacity for a prediction. A bad prediction is visible only as a cost line, which is why it is reported as waste rather than buried in utilisation.
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Solution Architecture v1.0 · open source on raw/bare-metal compute · Platform Architecture · 2026-1019-capacity-and-reclaim-loop