Moleculer Microservices Framework

Common errors

• Error: Missing transporter module.

  cause You configured a transporter (e.g., 'NATS', 'Redis') in your `ServiceBroker` options but did not install its corresponding npm package.
  fix Install the required package. For example, if using NATS, run `npm install nats` (or `yarn add nats`).

• TypeError: broker.call is not a function or broker.emit is not a function

  cause Attempting to call actions or emit events on the `ServiceBroker` instance before it has been started or after it has been stopped.
  fix Ensure `broker.start()` has successfully resolved before making any calls or emits. Wrap your logic within the `.then()` block of `broker.start()` or ensure a running broker instance.

• Service not found

  cause You are trying to call an action on a service that hasn't been created, registered, or is not available in the network.
  fix Verify the service name and action name are correct. Ensure the service is created with `broker.createService()` and the broker is started, allowing it to discover services across the network.

Warnings

• breaking Moleculer v0.15.0 significantly increased the minimum Node.js version requirement. It now requires Node.js >= 22.x.x.
  Fix: Upgrade your Node.js runtime to version 22 or newer. Ensure your deployment environment meets this requirement.
• breaking The Moleculer communication protocol has been changed in v0.15.0 to version 5. Nodes running v0.15.x will not be able to communicate with nodes running v0.14.x or older due to protocol incompatibility.
  Fix: All nodes in your Moleculer cluster must be upgraded to v0.15.0 simultaneously to maintain communication. Consider a phased rollout with caution, or a complete upgrade of the entire microservices mesh.
• breaking Schema-based serializers were removed from the core in v0.15.0. If you were relying on custom schema-based serializers, they need to be reimplemented or replaced with other serialization options.
  Fix: Review your serialization strategy. Moleculer still supports pluggable serializers like JSON, JSONExt, MsgPack, CBOR, and Notepack. Migrate to one of these or implement a custom serializer as a plugin.
• gotcha Moleculer relies heavily on various peer dependencies for its pluggable components (transporters, loggers, serializers, metrics, tracing). Forgetting to install the specific peer dependency for a chosen component will lead to runtime errors.
  Fix: Always install the required peer dependency for any specific transporter, logger, or other module you configure. For example, if using `transporter: 'NATS'`, you must `npm install nats`.
• gotcha When developing with TypeScript, ensure your `tsconfig.json` targets an ECMAScript version that supports `async/await` (e.g., `es2017` or higher) and includes `esnext.asynciterable` if using streams, and that `moduleResolution` is set to `node` or `nodenext`.
  Fix: Verify `"target": "es2017"` (or higher) and `"moduleResolution": "node"` or `"nodenext"` in your `tsconfig.json`. Consider adding `"lib": ["es2017", "esnext.asynciterable"]` for full type coverage.

Install

• npm install moleculer npm
• yarn add moleculer yarn
• pnpm add moleculer pnpm

Imports

• ServiceBroker
  wrong:

  const { ServiceBroker } = require('moleculer');

  correct:

  import { ServiceBroker } from 'moleculer';

  Moleculer v0.15 is primarily ESM-first. While CommonJS might still work in some setups, the recommended approach is ESM. `ServiceBroker` is the core class for creating and managing a broker instance.
• Service
  wrong:

  import Service from 'moleculer/service';

  correct:

  import { Service } from 'moleculer';

  The base class for defining services. Always imported as a named export from the main 'moleculer' package. For TypeScript, it's also the base class for type inference.
• ServiceSchema
  wrong:

  import { ServiceSchema } from 'moleculer/types';

  correct:

  import { ServiceSchema } from 'moleculer';

  The primary interface for defining service configurations and actions. It's a type, but also implicitly inferred when defining service objects.
• Transporters
  wrong:

  import { NatsTransporter } from 'moleculer/transporters/nats';

  correct:

  import { Transporters } from 'moleculer';

  Transporters namespace provides access to various built-in transporters like `Nats`, `Redis`, `Kafka`, etc. Generally accessed as `new Transporters.Nats(...)`.

Quickstart

This quickstart demonstrates how to create a basic Moleculer service, define actions and events, start the service broker, and then call an action and emit an event.

import { ServiceBroker, ServiceSchema } from 'moleculer';

// Create a ServiceBroker
const broker = new ServiceBroker({
  nodeID: 'node-greeter-1',
  logLevel: 'info',
  transporter: 'NATS' // Or 'Redis', 'TCP', etc.
});

// Define a Greeter Service
const GreeterService: ServiceSchema = {
  name: 'greeter',
  settings: {
    defaultName: 'World'
  },
  actions: {
    hello: {
      rest: 'GET /hello',
      async handler(ctx) {
        return `Hello ${ctx.params.name || this.settings.defaultName}`;
      }
    },
    welcome: {
      async handler(ctx) {
        this.logger.info(`Welcoming ${ctx.params.name}...`);
        return `Welcome, ${ctx.params.name}`;
      }
    }
  },
  events: {
    'user.created': {
      async handler(ctx) {
        this.logger.info(`User created event received for ${ctx.params.username}`);
      }
    }
  },
  async started() {
    this.logger.info(`Greeter service started on node ${broker.nodeID}`);
  },
  async stopped() {
    this.logger.info(`Greeter service stopped on node ${broker.nodeID}`);
  }
};

// Create a service from the schema
broker.createService(GreeterService);

// Start the broker
broker.start()
  .then(async () => {
    // Call an action
    const res = await broker.call('greeter.hello', { name: 'Moleculer' });
    console.log(res);

    // Emit an event
    await broker.emit('user.created', { username: 'Alice' });

    // Call an action from another node if available (assuming multiple nodes)
    const welcomeMsg = await broker.call('greeter.welcome', { name: 'Bob' });
    console.log(welcomeMsg);

    // Stop the broker after a delay or on signal
    setTimeout(() => broker.stop(), 5000);
  })
  .catch(err => {
    broker.logger.error('Error starting broker:', err);
  });