power-msk v2

Resilience-first KafkaJS helpers for production-grade apps on KafkaJS.

👉 Focused on robust consumers & producers + simple Koa middleware.

👉 You bring your own Kafka config (brokers, SSL, SASL, etc).

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✨ Features

Resilient Consumer

• Auto-recreate on fatal errors (STOP / CRASH with restart=false)
• Partition-level isolation via pause/resume
• Full-jitter exponential backoff
• Health & readiness probes

Resilient Producer

• Auto-reconnect & recreate on send errors
• Batching (lingerMs, maxBatchSize) for throughput
• Backpressure (maxQueueBytes) to prevent OOM
• Idempotence & transactions supported
• Health & readiness probes

Koa Middleware

• Exposes a shared resilient producer on ctx.kafkaClient
• sendMessages(), isHealthy(), isReady() available in requests
• Graceful shutdown hook (mw.shutdown()) for clean exits

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📦 Install

npm install @awsmag/power-msk kafkajs
# or
yarn add @awsmag/power-msk kafkajs

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🚀 Quickstart

1) Consumer (eachMessage)

import { Kafka } from "kafkajs";
import { ConsumerSupervisor } from "@awsmag/power-msk";

const kafka = new Kafka({
  clientId: "orders-app",
  brokers: ["b1:9092","b2:9092","b3:9092"],
  ssl: true,
});

const sup = new ConsumerSupervisor({
  kafka,
  groupId: "orders-g1",
  topics: ["orders"],
  eachMessage: async ({ topic, partition, message }) => {
    const payload = JSON.parse(message.value!.toString());
    console.log("Received", payload);
  },
});

await sup.startForever();

2) Consumer (eachBatch)

const sup = new ConsumerSupervisor({
  kafka,
  groupId: "orders-g1",
  topics: ["orders"],
  eachBatch: async ({ batch, commitOffsetsIfNecessary }) => {
    for (const m of batch.messages) {
      console.log("Received", m.offset, m.value?.toString());
    }
    await commitOffsetsIfNecessary();
  },
  runConfig: { autoCommit: false, eachBatchAutoResolve: false },
});

await sup.startForever();

3) Producer

import { ResilientProducer } from "@awsmag/power-msk";

const producer = new ResilientProducer({
  kafka,
  idempotent: true,
  acks: -1,
  lingerMs: 10,
  maxBatchSize: 500,
  maxQueueBytes: 5 * 1024 * 1024,
});

await producer.start();

await producer.sendOne("orders", {
  key: Buffer.from("o:123"),
  value: Buffer.from(JSON.stringify({ id: 123, status: "created" })),
});

4) Koa Middleware

import Koa from "koa";
import Router from "@koa/router";
import { getKafkaClientMw } from "@awsmag/power-msk";

const app = new Koa();
const router = new Router();

const kafkaMw = getKafkaClientMw({
  clientId: "my-app",
  brokers: ["b1:9092", "b2:9092"],
  ssl: true,
});

app.use(kafkaMw);

router.post("/broadcast", async (ctx) => {
  const events = [{ id: 1, msg: "hello" }];
  await ctx.kafkaClient!.sendMessages(events, "my-topic");
  ctx.status = 202;
});

router.get("/healthz", (ctx) => { ctx.status = ctx.kafkaClient!.isHealthy() ? 200 : 500; });
router.get("/readyz",  (ctx) => { ctx.status = ctx.kafkaClient!.isReady() ? 200 : 503; });

app.use(router.routes()).use(router.allowedMethods());
app.listen(3000);

// optional: stop producer cleanly in tests or shutdown scripts
// await kafkaMw.shutdown();

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🛠 API

ConsumerSupervisor

• startForever(): run until stopped
• stop(): graceful stop
• isHealthy() / isReady()

ResilientProducer

• start() / stop()
• send(topic, messages) / sendOne(topic, message)
• withTransaction(fn)
• isHealthy() / isReady()

Koa Middleware

• getKafkaClientMw(opts)

  • Attaches ctx.kafkaClient with:

    • sendMessages(events[], topic)
    • isHealthy()
    • isReady()

  • Provides .shutdown() for clean exits (esp. in tests)

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📚 Detailed Scenarios

Want to understand how the ConsumerSupervisor and ResilientProducer behave in real-world cases (errors, crashes, rebalances, backpressure)?

👉 See SCENARIOS.md for sequence diagrams and lifecycle walkthroughs.

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🔄 Migration (v1 → v2)

• IAM/MSK helpers dropped. Bring your own ssl/sasl.
• Producer/Consumer APIs are now resilience-focused.
• Koa middleware switched from per-request producer → shared resilient producer with auto-recreate.

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Maintained by AWSMAG C/O S25Digital.

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