Feat: add prometheus compatible endpoint, seed fallback store and add env.example

design.md

@@ -1,6 +1,7 @@
 # Ticket Scaling Microservice - Design Document
 
 ## Table of Contents
+
 1. [Architecture Overview](#architecture-overview)
 2. [System Components](#system-components)
 3. [Scalability Strategies](#scalability-strategies)
@@ -15,6 +16,7 @@
 ## Architecture Overview
 
 ### High-Level Architecture
+
 ```
 ┌─────────────────┐    ┌─────────────────┐    ┌─────────────────┐
 │   Load Balancer │    │   Prometheus    │    │    Grafana      │
@@ -38,6 +40,7 @@
 ```
 
 ### Design Principles
+
 1. **High Availability**: Fallback mechanisms ensure service continuity
 2. **Atomic Operations**: Redis Lua scripts prevent race conditions
 3. **Horizontal Scalability**: Stateless design enables easy scaling
@@ -47,6 +50,7 @@
 ## System Components
 
 ### 1. Core Application (server.js)
+
 - **Technology**: Node.js with Express framework
 - **Responsibilities**:
   - HTTP request handling
@@ -55,6 +59,7 @@
   - PDF generation coordination
 
 ### 2. Redis Client (redis-client.js)
+
 - **Technology**: Redis with Lua scripting
 - **Responsibilities**:
   - Atomic ticket operations
@@ -63,6 +68,7 @@
   - Script execution
 
 ### 3. Fallback Store (fallback-store.js)
+
 - **Technology**: In-memory JavaScript Map
 - **Responsibilities**:
   - Emergency ticket storage
@@ -70,6 +76,7 @@
   - Graceful degradation
 
 ### 4. PDF Generator (pdf-generator.js)
+
 - **Technology**: PDFKit library
 - **Responsibilities**:
   - Professional ticket generation
@@ -77,6 +84,7 @@
   - Cleanup operations
 
 ### 5. Logging System (logger.js)
+
 - **Technology**: Winston logging framework
 - **Responsibilities**:
   - Structured logging
@@ -87,6 +95,7 @@
 ## Scalability Strategies
 
 ### Horizontal Scaling
+
 ```
 ┌─────────────────┐    ┌─────────────────┐    ┌─────────────────┐
 │   Instance 1    │    │   Instance 2    │    │   Instance N    │
@@ -102,17 +111,20 @@
 ```
 
 **Key Features**:
+
 - Stateless application design
 - Shared Redis backend
 - Load balancer distribution
 - Independent scaling
 
 ### Vertical Scaling
+
 - **CPU**: Multi-core utilization through Node.js cluster mode
 - **Memory**: Configurable heap sizes for high-throughput
 - **I/O**: Async operations prevent blocking
 
 ### Database Scaling
+
 ```
 ┌─────────────────┐    ┌─────────────────┐    ┌─────────────────┐
 │   Redis Master  │    │  Redis Replica  │    │  Redis Replica  │
@@ -121,6 +133,7 @@
 ```
 
 **Strategies**:
+
 - Redis clustering for horizontal scaling
 - Read replicas for metrics/stats queries
 - Sharding by event ID for massive scale
@@ -128,6 +141,7 @@
 ## Atomic Operations
 
 ### Lua Script Design
+
 Our core purchase operation uses a Redis Lua script to ensure atomicity:
 
 ```lua
@@ -145,12 +159,14 @@ local globalKey = KEYS[3]  -- global:stats
 ```
 
 **Benefits**:
+
 - **Race Condition Prevention**: All operations execute atomically
 - **Consistency**: No partial state updates
 - **Performance**: Single round-trip to Redis
 - **Reliability**: All-or-nothing execution
 
 ### Concurrency Handling
+
 - **Optimistic Locking**: Lua scripts handle concurrent access
 - **Queue Management**: Redis lists provide FIFO ticket distribution
 - **Connection Pooling**: Efficient Redis connection reuse
@@ -158,11 +174,13 @@ local globalKey = KEYS[3]  -- global:stats
 ## Fallback Mechanisms
 
 ### Activation Triggers
+
 1. **Redis Connection Failure**: Network issues or Redis downtime
 2. **Script Execution Errors**: Lua script failures
 3. **Timeout Scenarios**: Slow Redis responses
 
 ### Fallback Architecture
+
 ```
 ┌─────────────────┐
 │  Request Comes  │
@@ -181,8 +199,16 @@ local globalKey = KEYS[3]  -- global:stats
 └─────────────────┘    └─────────────────┘
 ```
 
+### Fallback Store Improvements
+
+- **Automatic Seeding**: Fallback store is seeded during server startup and when activated
+- **Data Synchronization**: Automatic attempt to sync with Redis data when activated
+- **Manual Seeding**: Admin endpoint to manually populate fallback store from Redis
+- **Resilient Operation**: Continues functioning even when Redis is completely unavailable
+
 ### Fallback Limitations
-- **Non-Persistent**: Data lost on restart
+
+- **Non-Persistent**: Data lost on restart (mitigated by automatic reseeding)
 - **Single Instance**: No cross-instance synchronization
 - **Capacity Limited**: Memory constraints
 - **Warning Logs**: Clear indication of degraded mode
@@ -190,18 +216,21 @@ local globalKey = KEYS[3]  -- global:stats
 ## Performance Optimizations
 
 ### Application Level
+
 1. **Async Operations**: Non-blocking I/O throughout
 2. **Connection Pooling**: Reuse Redis connections
 3. **Batch Operations**: Bulk ticket seeding
 4. **Caching**: Event metadata caching
 
 ### Redis Optimizations
+
 1. **Lua Scripts**: Reduced network round-trips
 2. **Pipeline Operations**: Batch commands
 3. **Memory Management**: Efficient data structures
 4. **Persistence**: AOF for durability
 
 ### PDF Generation
+
 1. **Async Generation**: Non-blocking PDF creation
 2. **Stream Processing**: Memory-efficient file handling
 3. **Cleanup Jobs**: Automatic old file removal
@@ -210,6 +239,7 @@ local globalKey = KEYS[3]  -- global:stats
 ## Monitoring & Observability
 
 ### Metrics Collection
+
 ```json
 {
   "global": {
@@ -238,12 +268,14 @@ local globalKey = KEYS[3]  -- global:stats
 ```
 
 ### Logging Strategy
+
 - **Structured Logging**: JSON format for parsing
 - **Request Tracking**: Unique IDs for tracing
 - **Performance Metrics**: Response times and throughput
 - **Error Categorization**: Different log levels
 
 ### Health Checks
+
 - **Application Health**: `/health` endpoint
 - **Redis Connectivity**: Connection status
 - **Fallback Status**: Degraded mode indication
@@ -252,16 +284,19 @@ local globalKey = KEYS[3]  -- global:stats
 ## Security Considerations
 
 ### Input Validation
+
 - **Event ID Validation**: Numeric constraints
 - **Request Rate Limiting**: DDoS protection
 - **Parameter Sanitization**: Injection prevention
 
 ### Container Security
+
 - **Non-Root User**: Principle of least privilege
 - **Minimal Base Image**: Alpine Linux for smaller attack surface
 - **Health Checks**: Container monitoring
 
 ### Data Protection
+
 - **No Sensitive Data**: Tickets are identifiers only
 - **Audit Logging**: Purchase tracking
 - **Secure Defaults**: Production-ready configuration
@@ -269,6 +304,7 @@ local globalKey = KEYS[3]  -- global:stats
 ## Deployment Strategy
 
 ### Development Environment
+
 ```bash
 # Local development
 npm install
@@ -278,6 +314,7 @@ npm run dev          # Start with nodemon
 ```
 
 ### Production Environment
+
 ```bash
 # Docker deployment
 docker-compose up -d                    # Core services
@@ -285,6 +322,7 @@ docker-compose --profile monitoring up # With monitoring
 ```
 
 ### Container Orchestration
+
 - **Docker Compose**: Local and small deployments
 - **Kubernetes**: Large-scale deployments
 - **Health Checks**: Automatic restart on failure
@@ -293,24 +331,28 @@ docker-compose --profile monitoring up # With monitoring
 ## Future Enhancements
 
 ### Performance Improvements
+
 1. **Redis Clustering**: Horizontal database scaling
 2. **CDN Integration**: PDF delivery optimization
 3. **Caching Layer**: Application-level caching
 4. **Connection Optimization**: Advanced pooling
 
 ### Feature Additions
+
 1. **QR Code Generation**: Enhanced ticket security
 2. **Email Integration**: Automatic ticket delivery
 3. **Payment Processing**: Complete purchase flow
 4. **Event Management**: Dynamic event creation
 
 ### Monitoring Enhancements
+
 1. **Distributed Tracing**: Request flow tracking
 2. **Custom Dashboards**: Business metrics visualization
 3. **Alerting**: Proactive issue detection
 4. **Performance Profiling**: Bottleneck identification
 
 ### Security Hardening
+
 1. **Authentication**: API key management
 2. **Rate Limiting**: Advanced throttling
 3. **Encryption**: Data in transit protection