Add scalability documentation

scalability/cold-start-strategy.md

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+# Cold Start Strategy for New Containers
+
+## Overview
+
+A cold start occurs when the platform launches a new container because application traffic has increased and additional capacity is required.
+
+## Strategy
+
+### 1. Keep Warm Instances
+
+Maintain a small number of idle containers (2–3 replicas) that are always running and ready to receive traffic immediately.
+
+---
+
+### 2. Horizontal Auto Scaling
+
+Automatically create additional containers when one or more of the following conditions are met:
+
+- CPU usage exceeds 70%
+- Memory usage exceeds 75%
+- Request rate increases significantly
+- Response time exceeds the defined threshold
+
+---
+
+### 3. Fast Container Startup
+
+Reduce container startup time by:
+
+- Using lightweight Docker images
+- Installing only required packages
+- Minimizing application initialization
+- Preloading configuration files
+
+---
+
+### 4. Health Checks
+
+A new container should not receive production traffic until it successfully passes:
+
+- Readiness Probe
+- Health Check
+
+This ensures users are only routed to healthy containers.
+
+---
+
+### 5. Rolling Updates
+
+Deploy new application versions gradually to avoid downtime.
+
+Example:
+
+Old Version
+██████████
+
+↓
+
+New Version
+██░░░░░░░░
+
+↓
+
+████░░░░░
+
+↓
+
+██████████
+
+This strategy guarantees continuous service availability during deployments.