SKILL: Scaling & Capacity Plan Authoring

Domain: Performance Engineering, Capacity Planning, SDD Station 15 / 18

Activation triggers: scaling plan, capacity planning, traffic growth, horizontal scaling, bottleneck analysis, cloud infrastructure costs, SDD Station 15.

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1. Role & Threshold Law

The Scaling Plan Authoring skill evaluates and plans system behavior under extreme concurrency and data volume.
It enforces the Scale Threshold Law:

• The Scaling Plan is MANDATORY whenever:
  1. Traffic targets exceed 500 RPS or 10,000 DAU.
  2. Growth expectations anticipate > 10x scale within 12 months.
  3. Multi-region or multi-AZ active-active failover is required.
  4. The PRD contains explicit horizontal auto-scaling non-functional requirements.
• For internal tools or targets below these thresholds, the document may record a formal threshold exemption.

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2. Document Structure & Required Sections

Every generated Scaling Plan must follow .factory/specifications/templates/10_scaling_plan.template.md and contain:

• Header Metadata: Document ID, Version, Status, Parent PRD/Architecture IDs, Lead Performance Engineer, Date.
• Section 1: Applicability Threshold & Scale Trigger: Explicit justification of why the plan is required or exempt.
• Section 2: Capacity Baseline & Growth Projections:
  • Table showing Baseline (Current/MVP), Stage 1 (10x), and Stage 2 (Enterprise Scale/50x) across DAU, Peak RPS, Data Volume, and WebSocket connections.
• Section 3: Bottleneck Analysis by Architectural Layer:
  • In-depth risk, symptom, and mitigation analysis for:
    • Database & Persistence Tier (connection exhaustion, read replicas, partitioning).
    • Backend API & Compute Tier (CPU saturation, stateless containers, HPA).
    • Network & Ingestion Tier (bandwidth, CDN caching, rate limiting).
• Section 4: Horizontal vs. Vertical Scaling Strategy:
  • Matrix detailing scaling triggers and instance limits per container component.
• Section 5: Load Testing Benchmarks:
  • Concrete stress limits and degradation thresholds referenced from 09_testing_plan.md.
• Section 6: Infrastructure Cost Projections by Scale Tier:
  • Monthly cloud spend estimates and cost drivers across Baseline, Growth, and Enterprise tiers.
• Section 7: Signoff & Verification.

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3. Validation Checklist (Quality Gate G11 & G15 Pre-Condition)

• Clear threshold justification documented.
• Bottleneck mitigations defined for database, compute, and network.
• Auto-scaling triggers and container limits specified.
• Tiered cloud infrastructure costs estimated.
• Document saved to .factory/specifications/<project>/10_scaling_plan.md.