IMPLEMENTATION_COMPLETE.md

✅ Logging & Feature Flags Implementation Complete

This document summarizes the completed implementation of comprehensive request/response logging with correlation IDs and a feature flags system for Nestera.

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1️⃣ Request/Response Logging with Correlation IDs

✅ Completed Components

Backend (NestJS):

1. Correlation ID Middleware (src/common/middleware/correlation-id.middleware.ts)

   • ✅ Generates or accepts X-Correlation-ID headers
   • ✅ Attaches to req.correlationId for downstream use
   • ✅ Echoes back in response headers for distributed tracing
   • ✅ Records request start time for duration calculation

2. Correlation ID Interceptor (src/common/interceptors/correlation-id.interceptor.ts)

   • ✅ Safety net ensuring correlation IDs exist
   • ✅ Augments pino logger context

3. Request Logging Interceptor (src/common/interceptors/request-logging.interceptor.ts)

   • ✅ Logs incoming requests: method, URL, IP, user agent, user ID, masked wallet address
   • ✅ Logs outgoing responses: status code, duration, content length
   • ✅ Logs errors: stack traces (server errors only), error name, message
   • ✅ Skips noisy paths: /api/health, /api/metrics, /favicon.ico
   • ✅ Uses pino for structured JSON logs
   • ✅ Integrated with APM service: tracks HTTP requests and errors

4. Log Sanitizer Service (src/common/services/log-sanitizer.service.ts)

   • ✅ Redacts sensitive headers: Authorization, Cookie, X-API-Key
   • ✅ Redacts sensitive body fields: password, secret, token, privateKey, mnemonic, seedPhrase
   • ✅ Detects and redacts Stellar secret keys: S[A-Z2-7]{55}
   • ✅ Truncates long values to 500 chars
   • ✅ Masks wallet addresses to first 6 + last 4 chars

5. Pino Configuration (src/app.module.ts)

   • ✅ Correlation ID injection via customProps
   • ✅ Automatic redaction of sensitive fields
   • ✅ Structured serializers for req/res/err
   • ✅ Pretty printing in dev with pino-pretty
   • ✅ JSON logs in production
   • ✅ File-based log retention: configurable via LOG_DIR and LOG_RETENTION_DAYS env vars

6. APM Integration (src/modules/apm/)

   • ✅ ApmService: tracks HTTP requests, errors, database queries, user events
   • ✅ MetricsService: Prometheus-compatible metrics (counters, histograms, gauges)
   • ✅ DistributedTracingService: W3C Trace Context support, span tracking
   • ✅ ApmInterceptor: distributed tracing with traceparent headers
   • ✅ Wired into RequestLoggingInterceptor for automatic tracking

Frontend (Next.js):

1. Monitoring Library (app/lib/monitoring.ts)

   • ✅ Lightweight wrapper around Sentry (CDN-loaded)
   • ✅ Privacy-compliant: never captures passwords, private keys, raw addresses
   • ✅ Tracks breadcrumbs, user context, API errors, wallet errors
   • ✅ Gracefully no-ops when Sentry DSN not configured

2. MonitoringProvider (app/components/MonitoringProvider.tsx)

   • ✅ Injects Sentry via Script component
   • ✅ Initializes global error and unhandled rejection handlers
   • ✅ Tracks navigation as breadcrumbs
   • ✅ Attaches privacy-safe wallet user context (truncated address + network)

📋 Usage Examples

Backend logs:

{
  "msg": "→ POST /api/v2/auth/login",
  "type": "REQUEST",
  "correlationId": "a1b2c3d4-...",
  "method": "POST",
  "url": "/api/v2/auth/login",
  "ip": "192.168.1.100",
  "timestamp": "2026-06-02T10:15:30.123Z"
}

APM dashboard:

• Visit /api/apm/dashboard (authenticated) for metrics, errors, traces
• Visit /api/apm/metrics for Prometheus-compatible metrics

Frontend error tracking:

import { captureApiError, trackUserAction } from "@/lib/monitoring";

// Track API errors
captureApiError(error, "/api/v2/savings/goals", 500, "POST");

// Track user actions
trackUserAction("savings_goal_created", { amount: 1000, currency: "USDC" });

🔧 Configuration

Backend .env:

LOG_DIR=/var/log/nestera           # Optional: file-based logging
LOG_RETENTION_DAYS=30              # Log retention policy
APM_SAMPLING_RATE=1.0              # Distributed tracing sampling (0.0-1.0)

Frontend .env:

NEXT_PUBLIC_SENTRY_DSN=https://...@sentry.io/...
NEXT_PUBLIC_SENTRY_ENVIRONMENT=production
NEXT_PUBLIC_SENTRY_RELEASE=v1.2.3

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2️⃣ Feature Flags System

✅ Completed Components

Backend (NestJS):

1. Feature Flag Module (src/modules/feature-flags/)

   • ✅ Entity (entities/feature-flag.entity.ts): TypeORM entity with full flag config
   • ✅ Service (feature-flags.service.ts): CRUD operations + evaluation logic
   • ✅ Controller (feature-flags.controller.ts): REST API endpoints
   • ✅ DTOs (dto/create-flag.dto.ts, dto/update-flag.dto.ts): validation schemas
   • ✅ Migration (migrations/1775300000000-CreateFeatureFlagsTable.ts): database schema

2. API Endpoints:

   • ✅ GET /api/v2/feature-flags — fetch all flags (public)
   • ✅ GET /api/v2/feature-flags/:key/evaluate — evaluate flag for user context (public)
   • ✅ GET /api/v2/feature-flags/:key — get single flag (admin)
   • ✅ POST /api/v2/feature-flags — create flag (admin)
   • ✅ PUT /api/v2/feature-flags/:key — update flag (admin)
   • ✅ PATCH /api/v2/feature-flags/:key/toggle — toggle flag (admin)
   • ✅ DELETE /api/v2/feature-flags/:key — delete flag (admin)

3. Evaluation Logic:

   • ✅ Kill switches (force disable)
   • ✅ User targeting (wallet address)
   • ✅ Network targeting (public/testnet)
   • ✅ Segment targeting (beta_tester, internal)
   • ✅ Percentage rollout (consistent hashing)

Frontend (Next.js):

1. Feature Flag Engine (app/lib/feature-flags.ts)

   • ✅ Flag types: boolean, string, number, rollout
   • ✅ Targeting rules: users, networks, segments, rollout percentage
   • ✅ Kill switches
   • ✅ LocalStorage cache + API sync
   • ✅ Privacy-safe hashing for A/B bucketing
   • ✅ Tracks flag evaluations as monitoring breadcrumbs

2. Configuration (app/lib/flags.config.ts)

   • ✅ Default flags seeded on first load
   • ✅ 10+ predefined flags (dashboard, charts, wallet, A/B tests, kill switches, beta features)

3. Context Provider (app/context/FeatureFlagContext.tsx)

   • ✅ State management for flags and loading state
   • ✅ Admin functions: toggle, update, create, delete
   • ✅ User context syncing for targeting (wallet address, network)
   • ✅ Automatic merging of defaults with API-loaded and cached flags

4. Hooks (app/hooks/useFeatureFlag.ts)

   • ✅ useFeatureFlag(key) — boolean flags
   • ✅ useFeatureFlagValue<T>(key) — multivariate flags
   • ✅ useFeatureFlagMany(keys) — batch check

5. Admin UI (app/components/FeatureFlagAdmin.tsx)

   • ✅ Slide-in panel accessible via TopNav flag icon (dev mode only)
   • ✅ Search, filter by tag (all/enabled/disabled/kill_switch/experiment/beta)
   • ✅ Live toggle, rollout percentage slider, kill switch controls
   • ✅ Create/delete flags at runtime

📋 Usage Examples

Component usage:

import { useFeatureFlag } from "@/hooks/useFeatureFlag";

export default function Dashboard() {
  const { isEnabled, isLoading } = useFeatureFlag("new-dashboard-layout");

  if (isLoading) return <Skeleton />;
  if (isEnabled) return <NewDashboard />;
  return <OldDashboard />;
}

Multivariate flags:

const { value } = useFeatureFlagValue<string>("ab-cta-button-color");
// value === "teal" | "green"

Admin UI:

• Open dashboard → Click flag icon in TopNav (dev mode)
• Toggle flags, adjust rollout percentages, create new flags

🔧 Configuration

Backend .env:

# No additional config required.
# Flags are stored in the database.

Frontend .env:

NEXT_PUBLIC_API_URL=https://api.nestera.io  # For flag API sync

🚀 Migration

Run the migration to create the feature_flags table:

cd backend
npm run typeorm migration:run

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🎯 Acceptance Criteria Status

Request/Response Logging:

• ✅ Correlation ID middleware implemented
• ✅ All incoming requests logged with metadata
• ✅ All outgoing responses logged
• ✅ Integrated with APM service
• ✅ Log retention policies configurable
• ✅ Log sanitization for sensitive data

Feature Flags:

• ✅ Feature flag system implemented
• ✅ Flags can be toggled without deployment
• ✅ User-based targeting works
• ✅ Flag state persists correctly
• ✅ Admin UI for managing flags
• ✅ Flag analytics tracked
• ✅ Documentation for developers
• ✅ No performance impact (caching, efficient evaluation)

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📚 Documentation

• Logging: See LOGGING_IMPLEMENTATION.md for detailed backend logging architecture
• Feature Flags: See FEATURE_FLAGS_IMPLEMENTATION.md for frontend flag system
• APM: Visit /api/v2/docs and look for the "APM" tag
• Feature Flags API: Visit /api/v2/docs and look for the "Feature Flags" tag

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🔐 Security Notes

1. Logging:

   • All sensitive fields automatically redacted before logging
   • Wallet addresses masked to first 6 + last 4 chars
   • Stack traces only logged for server errors (not client errors)
   • Correlation IDs are UUIDs, not predictable

2. Feature Flags:

   • Public endpoints (GET /feature-flags) return non-sensitive config only
   • Admin endpoints (POST, PUT, DELETE) require JWT authentication
   • User targeting uses truncated wallet addresses (first 10 chars) for privacy
   • Rollout bucketing uses one-way hashing (consistent but not reversible)

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🧪 Testing

Backend:

cd backend

# Test correlation IDs
curl -H "X-Correlation-ID: test-123" http://localhost:3001/api/health
# Response includes: X-Correlation-ID: test-123

# Fetch feature flags
curl http://localhost:3001/api/v2/feature-flags

# Evaluate a flag
curl "http://localhost:3001/api/v2/feature-flags/new-dashboard-layout/evaluate?address=GABCD...&network=public"

Frontend:

1. Open dashboard
2. Click flag icon in TopNav (dev mode)
3. Toggle a flag → see changes reflected immediately
4. Check browser console → Sentry breadcrumbs logged

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🎉 Summary

Logging:

• ✅ Full distributed tracing with correlation IDs
• ✅ Structured JSON logs with automatic sanitization
• ✅ APM integration with metrics, errors, and traces
• ✅ File-based log retention configurable
• ✅ Sentry monitoring on frontend

Feature Flags:

• ✅ Runtime toggles without deployment
• ✅ User-based, network-based, segment-based targeting
• ✅ A/B testing with percentage rollouts
• ✅ Kill switches for emergency disabling
• ✅ LocalStorage + API sync for persistence
• ✅ Admin UI for flag management
• ✅ Complete API for backend flag control

Both systems are production-ready, privacy-compliant, and fully integrated with the existing Nestera architecture.