Using Singleton Logger class in Nestjs

Question

I have a web application on Nest.js where I make use of pino to log exceptions .

Service1.ts

import {Logger} from 'nestjs-pino';

export class Service1{
constructor(private readonly logger : Logger) {}

async Do()
{

...
 this.logger.log("Log1");
}
}

Service2.ts

import {Logger} from 'nestjs-pino';

export class Service2{
constructor(private readonly logger : Logger) {}

async DoOtherWork()
{

...
 this.logger.log("Log1");
}
}

Since the Service files will be called from multiple UI operations so my understanding is multiple Logger classes will be created . So , is it a good idea to have Logger as a Singleton class ?

How can I make changes to the Nest.js application to have Logger as a singleton class with thread safety?

Yes you can use middleware concept of nestjs and create a logger middleware — Kazi Akib Javed
– Kazi Akib Javed, Commented Mar 19 at 4:48

jkaos92 · Accepted Answer · 2025-03-17 14:55:17Z

In NestJS, the Logger from nestjs-pino is already designed to be a singleton when injected properly as a provider. If you directly instantiate it in the service, it won't be a singleton.

If you do:

import { Module } from '@nestjs/common';
import { LoggerModule } from 'nestjs-pino';

@Module({
  imports: [
    LoggerModule.forRoot({
      pinoHttp: {
        level: 'info', 
      },
    }),
  ],
  exports: [LoggerModule], 
})
export class AppModule {}

and service1

import { Injectable } from '@nestjs/common';
import { Logger } from 'nestjs-pino';

@Injectable()
export class Service1 {
  constructor(private readonly logger: Logger) {}

  async Do() {
    this.logger.log('Log1');
  }
}

and service2

import { Injectable } from '@nestjs/common';
import { Logger } from 'nestjs-pino';

@Injectable()
export class Service2 {
  constructor(private readonly logger: Logger) {}

  async DoOtherWork() {
    this.logger.info('Log2');
  }
}

and have a module like this:

import { Module } from '@nestjs/common';
import { Service1 } from './service1';
import { Service2 } from './service2';

@Module({
  providers: [Service1, Service2],
  exports: [Service1, Service2],
})
export class SomeModule {}

The same Logger instance will be injected into Service1 and Service2.

What i think you are interested is set the context for the service, the nestjs-pino documentation mentions that:

export class MyService {
  constructor(
    private readonly logger: PinoLogger
  ) {
    // Optionally you can set context for logger in constructor or ...
    this.logger.setContext(MyService.name);
  }

  constructor(
    // ... set context via special decorator
    @InjectPinoLogger(MyService.name)
    private readonly logger: PinoLogger
  ) {}

  foo() {
    // PinoLogger has same methods as pino instance
    this.logger.trace({ foo: 'bar' }, 'baz %s', 'qux');
    this.logger.debug('foo %s %o', 'bar', { baz: 'qux' });
    this.logger.info('foo');
  }
}

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