nestjs/nest · error · Error

Method is not supported in gRPC mode.

Error message

Method is not supported in gRPC mode.

What it means

`ClientGrpcProxy.on(event, callback)` throws because the connection-event-emitter API (`on('connected', ...)`) is not supported for gRPC. The signature `EventKey extends never` also makes this statically impossible to call with any real event name. Connection lifecycle is managed internally by grpc-js.

Source

Thrown at packages/microservices/client/client-grpc.ts:396

  }

  protected publish(packet: any, callback: (packet: any) => any): any {
    throw new Error(
      'Method is not supported in gRPC mode. Use ClientGrpc instead (learn more in the documentation).',
    );
  }

  protected async dispatchEvent(packet: any): Promise<any> {
    throw new Error(
      'Method is not supported in gRPC mode. Use ClientGrpc instead (learn more in the documentation).',
    );
  }

  public on<EventKey extends never = never, EventCallback = any>(
    event: EventKey,
    callback: EventCallback,
  ) {
    throw new Error('Method is not supported in gRPC mode.');
  }

  public unwrap<T>(): T {
    throw new Error('Method is not supported in gRPC mode.');
  }
}

View on GitHub (pinned to 6ec0e2783d)

Solutions

1. Remove the `on()` call for gRPC clients; rely on per-call Observables and their error callback.
2. Branch status-reporting code by transport type.
3. If you need grpc-js channel-state events, access the underlying client via `getService()` callbacks (note `unwrap()` is also unsupported).

Example fix

// before
client.on('connected', () => logger.log('gRPC ready'));
// after
const math = client.getService<MathClient>('Math');
math.sum({ data: [1] }).subscribe({
  next: r => logger.log('gRPC call ok', r),
  error: e => logger.error('gRPC call failed', e),
});

import { ClientGrpc } from '@nestjs/microservices';
// gRPC clients do not support on(); subscribe to per-call Observables instead
if (!('on' in client)) { /* skip */ }

import { ClientGrpc } from '@nestjs/microservices';
function isGrpcClient(c: unknown): c is ClientGrpc {
  return typeof c === 'object' && c !== null && typeof (c as any).getService === 'function';
}

When it happens

Trigger: Calling `clientGrpc.on('connected', cb)` (or any event) on a gRPC client proxy.

Common situations: Generic status/health reporting code that subscribes to events on every `ClientProxy`; copy-paste from another transport's connection handler.

Related errors

• The "connect()" method is not supported in gRPC mode.
• Method is not supported in gRPC mode. Use ClientGrpc instead
• 3
• Not initialized. Please call the "connect" method first.
• No consumer initialized. Please, call the "connect" method f

AI-assisted analysis of nestjs/nest@6ec0e2783d (2026-08-03). Data as JSON: /data/errors/748a7adea0420dcb.json. Report an issue: GitHub.