Autoscaling Controller  ·  View 26 of 37  ·  4 · Runtime

When the Capacity Is Not There

Stockout, quota and scarcity are one problem; throttling is a different one.

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Request Provision Request preferred shape Refusal Zonal Stockout Quota Exhausted Accelerator Scarce API Throttled different problem Declared fallback Next Zone ordered list Next Shape declared only Spot then On-Demand above the floor Exhausted Unmet Demand Signal surfaced, not retried Alert capacity constrained Meanwhile Hold What Serves no scale-in Time Constrained reported per target breaker, not fallback degrade, keep serving When the Capacity Is Not There Application we own Risk / gap Security / platform Data store failure / alternate synchronous Throttling and scarcity look alike and are handled differently: throttling is retried with backoff behind a breaker, scarcity is a fallback list and then an honest signal. v 1.0 · owner Data & AI Global Practice · date 2026-09

Decisions

  • Scarcity walks a declared ordered list of zones and machine shapes, then surfaces unmet demand. It never retries indefinitely.
  • Throttling is not scarcity: it backs off with jitter behind a per-provider concurrency cap and a breaker that opens after 5 failures.
  • While constrained the controller holds what is serving and does not scale in. Time-constrained is reported per target.

Spot capacity

  • Declared targets prefer interruptible capacity above an on-demand floor the controller never falls below.
  • A spot eviction is observed as a drop in actual capacity and re-derived on the next reconcile, which is the same path as any other partial loss.

Risks

  • A fallback list that is too permissive silently changes a target's performance profile. Shapes must be declared per target, never inferred.
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Solution Architecture v1.0 · Data & AI Global Practice · 2026-09 · 37 views · Azure and open source26-capacity-unavailability