Complete Q4: Add architecture diagram, capacity sizing, cold start, and block storage docs

q4-scalability/README.md

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+# Question 4: Scalability, Load Balancing & Block Storage Strategy
+
+## 1. High-Scale System Architecture Diagram (15,000 req/s)
+
+```text
+                                  [ Ghaymah DNS / CDN ]
+                                            │
+                                            ▼
+                              [ Ghaymah Load Balancer (ALB) ]
+                                            │
+               ┌────────────────────────────┼────────────────────────────┐
+               ▼                            ▼                            ▼
+      [ Pod / Container 1 ]        [ Pod / Container 2 ]    ...  [ Pod / Container N ]
+   (Stateless Application Layer - Auto-scaled via HPA: Min 40 / Max 60 Pods)
+               │                            │                            │
+               └────────────────────────────┼────────────────────────────┘
+                                            │
+                     ┌──────────────────────┴──────────────────────┐
+                     ▼                                             ▼
+       [ Ghaymah In-Memory Cache ]                    [ Ghaymah Stateful Workloads ]
+      (Redis Cluster for Sessions)                 (StatefulSet + Ghaymah Block Storage)
+Container Sizing & Capacity CalculationsTarget Throughput: $15,000\text{ req/s}$Max Throughput per Container: $500\text{ req/s}$Base Container Requirement:$$\text{Base Containers} = \frac{15,000}{500} = 30\text{ containers}$$Safety Margin Buffer (30% Overhead):Option A (Adding 30% extra node capacity): $30 \times 1.30 = 39\text{ containers}$Option B (Targeting 70% max utilization per container): $\frac{15,000}{350\text{ req/s}} = 42.85 \implies 43\text{ containers}$Deployment Recommendation: Set initial HPA baseline to 40 replicas with auto-scaling limits between 39 to 60 containers.3. Cold Start Mitigation Strategy for New ContainersTo eliminate container startup latency during burst auto-scaling events:Lightweight Container Images: Use minimal multi-stage Docker builds (Alpine/Distroless) to reduce pull and extraction time.Kubernetes Readiness & Startup Probes: Separate heavy initialization from readiness checks so traffic is routed only when application memory is warm.Pre-warmed Buffer Capacity: Configure HPA with a conservative scale-down stabilization window and preemptive predictive scaling.Lazy Initialization: Defer non-critical background module loading until after the main web server accepts requests.4. Ghaymah Block Storage for Stateful WorkloadsGhaymah Block Storage provides low-latency, high-IOPS persistent storage for stateful applications (Databases, Message Queues):PersistentVolumeClaims (PVC): Dynamically provisions dedicated block volumes attached directly to Kubernetes StatefulSet pods.Data Consistency & Isolation: High-performance storage isolated per database instance (e.g., PostgreSQL / MongoDB data directories).Snapshot & Disaster Recovery: Enables automated point-in-time volume snapshots without service interruption.EOF