gRPC x Moleculer

Receive and send gRPC traffic from code written with the Moleculer framework. This can be helpful for migrating away from the piecemeal communication protocol Moleculer uses.

Important

This code isn't maintained/heavily supported. It was written to solve problems with a particular deployment of Moleculer so it brings plenty of opinions. Though I'm happy to help with specific issues, I figure organizations running into issues this would solve have the engineering people to run with what's available here. 🙂

How to

This project provides examples for both:

• Server: Receive requests to Moleculer actions through gRPC
• Client: Send requests through gRPC

Since, being a framework + having a loose API, there are lots of ways to implement Moleculer a npm package isn't available. The code here assumes a particular response format and gRPC services exposed through Kubernetes services going through linkerd. I haven't spent the time to propagate tracing details.

That said, there are mixins covering JSON serialized payloads.

const { ServiceBroker } = require('moleculer');
const { startGrpcServer, GrpcClientMixin } = require('@org/moleculer-grpc-bridge');

const broker = new ServiceBroker();

broker.createService({
  name: 'scheduler',

  mixins: [
    // Requests leaving `scheduler` which pass the `shouldCallThroughGrpc` predicate
    // will be sent to a gRPC service.
    new GrpcClientMixin(broker, {
      shouldCallThroughGrpc: async (name, params, opts) => {
        // - Look at an environment variable
        // - Load a configuration
        // - whatever works!
        return true;
      },
    }),
  ],
  async started() {
    await startGrpcServer(this.actions);
  },
  actions: {
    // ...
  },
});

Tests

Tested against:

• Node v18
• Moleculer v0.14.22
• gRPC JS v1.8 over HTTP/2 via linkerd 2.13

Probably works / minimums:

• Node v16+
• Moleculer v0.12.0+
• gRPC v1