kafka-pub-sub/examples/ecommerce/consumer.js

Enterprise-grade Kafka publish/subscribe library for Node.js — producer pool, batch sending, DLQ, SSL/SASL, multi-broker, and real-world industry examples.

/**
 * E-Commerce Order Pipeline — Consumers
 *
 * Each service listens to its own topic and processes the event.
 * All consumers run in parallel in this demo; in production each would
 * be a separate microservice with its own Node process.
 *
 * Run:
 *   node examples/ecommerce/consumer.js
 */

require('dotenv').config({ path: require('path').resolve(__dirname, '../../.env') });

const { ConsumeEvent } = require('../../index');

// eslint-disable-next-line no-console
const log = (service, ...args) =>
  console.log(`[${new Date().toISOString()}] [${service}]`, ...args);

// ── Inventory Service ─────────────────────────────────────────────────────────
async function startInventoryService() {
  const stop = await ConsumeEvent(
    'order.placed',
    async (msg) => {
      const { orderId, items } = msg.value.data || msg.value;
      log('INVENTORY', `Processing reservation for order ${orderId}`);

      // Simulate stock check per item
      items.forEach((item) => {
        log('INVENTORY', `  Reserving ${item.qty}x ${item.sku}`);
      });

      // In production: update inventory DB, emit inventory.reserve event
      log('INVENTORY', `✓ Reserved stock for order ${orderId}`);
    },
    {
      groupId: 'inventory-service',
      fromBeginning: false,
      retry: 3,
      dlq: true,
    }
  );

  return stop;
}

// ── Payment Service ───────────────────────────────────────────────────────────
async function startPaymentService() {
  const stop = await ConsumeEvent(
    'inventory.reserve',
    async (msg) => {
      const payload = msg.value.data || msg.value;
      log('PAYMENT', `Processing payment for order ${payload.orderId}`);

      // Simulate payment gateway call
      await new Promise((r) => setTimeout(r, 50)); // fake latency
      log('PAYMENT', `✓ Payment authorised for order ${payload.orderId}`);
    },
    {
      groupId: 'payment-service',
      fromBeginning: false,
      retry: 5, // payments get more retries
      dlq: true,
    }
  );

  return stop;
}

// ── Notification Service ──────────────────────────────────────────────────────
async function startNotificationService() {
  const stop = await ConsumeEvent(
    'fulfillment.ship',
    async (msg) => {
      const payload = msg.value.data || msg.value;
      log('NOTIFICATION', `Sending shipping confirmation for order ${payload.orderId}`);
      log('NOTIFICATION', `  Carrier: ${payload.shippingCarrier} | ETA: ${payload.estimatedDelivery}`);
      // In production: send email/SMS/push via SES, Twilio, FCM
      log('NOTIFICATION', `✓ Shipping notification sent for order ${payload.orderId}`);
    },
    {
      groupId: 'notification-service',
      fromBeginning: false,
      retry: 2,
      dlq: true,
    }
  );

  return stop;
}

// ── Audit / Observability Service ────────────────────────────────────────────
async function startAuditService() {
  const topics = ['order.placed', 'payment.charge', 'fulfillment.ship'];

  const stops = await Promise.all(
    topics.map((topic) =>
      ConsumeEvent(
        topic,
        async (msg) => {
          log(
            'AUDIT',
            `[${topic}] offset=${msg.offset} key=${msg.key} correlationId=${msg.headers['correlation-id'] || 'n/a'}`
          );
        },
        { groupId: 'audit-service', fromBeginning: false }
      )
    )
  );

  return () => Promise.all(stops.map((s) => s()));
}

// ── Main ──────────────────────────────────────────────────────────────────────
async function main() {
  log('SYSTEM', 'Starting e-commerce consumers (Ctrl+C to stop)...');

  const [stopInventory, stopPayment, stopNotification, stopAudit] = await Promise.all([
    startInventoryService(),
    startPaymentService(),
    startNotificationService(),
    startAuditService(),
  ]);

  log('SYSTEM', '✓ All consumers running');

  // Graceful shutdown — already handled inside ConsumeEvent,
  // but we can do extra cleanup here too.
  const shutdown = async () => {
    log('SYSTEM', 'Shutting down...');
    await Promise.all([stopInventory(), stopPayment(), stopNotification(), stopAudit()]);
    log('SYSTEM', 'Goodbye.');
    process.exit(0);
  };

  process.on('SIGTERM', shutdown);
  process.on('SIGINT', shutdown);
}

main().catch((err) => {
  // eslint-disable-next-line no-console
  console.error('Consumer startup failed:', err);
  process.exit(1);
});