refactor: reorganize directory structure to match exam submission spec

q4-scalability/calculations.md

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+# Capacity Planning: Handling 15,000 req/s
+
+To ensure high availability and responsiveness under a load of 15,000 requests per second, we must calculate the required number of container instances.
+
+## Base Assumptions
+- **Target Load:** 15,000 req/s
+- **Max Capacity per Container:** 500 req/s
+- **Safety Margin:** 30%
+
+## Calculation
+1. **Effective Capacity per Container:** 
+   To maintain a 30% margin, we calculate the effective capacity each container should handle before we consider scaling out.
+   `500 req/s * (1 - 0.30) = 350 req/s`
+
+2. **Total Containers Required:**
+   Divide the total expected load by the effective capacity per container.
+   `15,000 req/s / 350 req/s per container ≈ 42.85`
+
+3. **Rounding Up:**
+   We cannot have a fraction of a container, so we always round up to the next whole number.
+   `ceil(42.85) = 43 containers`
+
+## Conclusion
+To safely handle 15,000 req/s while maintaining a 30% safety margin (which helps absorb sudden traffic spikes or the failure of a few containers), the auto-scaling group should be configured to maintain a baseline of **43 containers** during peak load.