Structured logging: từ console.log đến log có thể query được

[2026-05-02 03:12:44] INFO: User logged in
[2026-05-02 03:12:44] ERROR: connection refused
[2026-05-02 03:12:45] INFO: Request completed in 234ms
[2026-05-02 03:12:45] WARN: Slow query detected

{
  "timestamp": "2026-05-02T03:12:44.312Z",
  "level": "error",
  "service": "auth-service",
  "traceId": "tr_4f8a2b1c9d3e",
  "userId": "u_8af2c3",
  "message": "Redis connection refused",
  "error": {
    "name": "ConnectionError",
    "message": "connect ECONNREFUSED 10.0.1.45:6379",
    "stack": "ConnectionError: connect ECONNREFUSED..."
  },
  "durationMs": 1203,
  "host": "auth-pod-7d9f4b-xkp2m"
}

-- Tìm tất cả lỗi Redis của một user cụ thể trong 30 phút
fields @timestamp, traceId, userId, error.message
| filter level = "error"
  AND service = "auth-service"
  AND userId = "u_8af2c3"
  AND error.message like /ECONNREFUSED/
| sort @timestamp desc
| limit 20

// middleware/correlationId.ts
import { Request, Response, NextFunction } from "express";
import { v4 as uuidv4 } from "uuid";

export function correlationIdMiddleware(
  req: Request,
  res: Response,
  next: NextFunction
): void {
  // Nhận từ upstream service nếu có, hoặc tự generate mới tại entry point
  const traceId =
    (req.headers["x-trace-id"] as string) ??
    `tr_${uuidv4().replace(/-/g, "").slice(0, 12)}`;

  req.traceId = traceId;
  res.setHeader("X-Trace-Id", traceId);

  next();
}

// Khi gọi downstream service, LUÔN truyền traceId
async function callPaymentService(traceId: string, payload: PaymentPayload) {
  return await fetch("https://payment-service.internal/payments", {
    method: "POST",
    headers: {
      "Content-Type": "application/json",
      "X-Trace-Id": traceId, // Truyền tiếp để payment service log cùng traceId
    },
    body: JSON.stringify(payload),
  });
}

// logger/index.ts
import pino from "pino";

const logger = pino({
  level: process.env.LOG_LEVEL ?? "info",
  // Pretty print chỉ ở local development
  transport:
    process.env.NODE_ENV === "development"
      ? { target: "pino-pretty", options: { colorize: true } }
      : undefined,
  // Các field xuất hiện trong mọi dòng log
  base: {
    service: process.env.SERVICE_NAME ?? "unknown-service",
    version: process.env.APP_VERSION ?? "unknown",
    env: process.env.NODE_ENV ?? "development",
  },
  timestamp: pino.stdTimeFunctions.isoTime,
});

export default logger;

// logger/requestLogger.ts — middleware log mỗi request
import { Request, Response, NextFunction } from "express";
import logger from "./index";

export function requestLogger(
  req: Request,
  res: Response,
  next: NextFunction
): void {
  const startTime = Date.now();

  // Child logger bind context của request — KHÔNG truyền traceId vào từng log call
  const reqLogger = logger.child({
    traceId: req.traceId,
    userId: (req as any).user?.id,
    method: req.method,
    path: req.path,
    ip: req.ip,
  });

  // Gắn vào request để handler dùng thay vì import logger trực tiếp
  (req as any).log = reqLogger;

  res.on("finish", () => {
    const durationMs = Date.now() - startTime;
    const level =
      res.statusCode >= 500 ? "error" : res.statusCode >= 400 ? "warn" : "info";

    reqLogger[level](
      {
        statusCode: res.statusCode,
        durationMs,
        slow: durationMs > 1000, // Flag để alert slow request
      },
      `${req.method} ${req.path} ${res.statusCode} ${durationMs}ms`
    );
  });

  next();
}

// Sampling strategy cho high-frequency endpoint
// Log 100% 4xx/5xx, chỉ log 1% request 2xx thông thường
function shouldLogRequest(statusCode: number): boolean {
  if (statusCode >= 400) return true; // Lỗi: log tất cả
  return Math.random() < 0.01; // Thành công: sample 1%
}

// utils/logSanitizer.ts
const SENSITIVE_KEYS = new Set([
  "password",
  "token",
  "secret",
  "authorization",
  "creditCard",
  "cvv",
  "ssn",
  "apiKey",
  "refreshToken",
]);

export function sanitizeForLog(
  obj: Record<string, unknown>
): Record<string, unknown> {
  return Object.fromEntries(
    Object.entries(obj).map(([key, value]) => {
      // Redact hoàn toàn các field nhạy cảm
      if (SENSITIVE_KEYS.has(key.toLowerCase())) {
        return [key, "[REDACTED]"];
      }
      // Mask email một phần: [email protected] → u***@domain.com
      if (typeof value === "string" && key === "email" && value.includes("@")) {
        const [local, domain] = value.split("@");
        return [key, `${local[0]}***@${domain}`];
      }
      return [key, value];
    })
  );
}

// Dùng khi cần log request context
logger.error(
  {
    traceId: req.traceId,
    context: sanitizeForLog(req.body), // Không log body thô
  },
  "Payment failed"
);