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NestJS Logger

A Nest.js production-ready logger implementation.

Introduction

This project implements a production-ready logger for Nest.js applications using Winston and Morgan on a clean architecture (Hexagonal Architecture).

You can read a detailed explanation of the project on the following article: https://medium.com/p/d03e3bb56772/edit

That implements a production-ready system advanced or basic Microservices or Monoliths projects applying concepts like:

  • Correlation IDs
  • Decoupled log transporters
  • Log levels
  • Logging Rules
  • Log formatters

Project structure

The project is structured in a Nest.js monorepo.

The folder structure is as follows:

  • apps: It contains the project's executable applications, in this case, the REST API.
    • api: It contains the REST API developed with Nest.js.
  • libs: It contains the project packages or Bounded Contexts on a DDD language.
    • shared: It contains the code of the Shared Kernel.
      • src: It contains the source code.
        • config: It contains de config module.
        • context: It contains the context module.
        • logger: It contains the logger module.

Key concepts

Architecture

The project is structured on a Hexagonal Architecture, so it has the following layers:

  • Application
  • Domain
  • Infrastructure

Logging Libraries

We use Winston to manage the logs and Morgan to log the HTTP requests. All that is managed by the LoggerModule.

To manage Winston transports, we use the WinstonLoggerTransportsKey DI token that is defined on the LoggerModule.

Decoupling Logging library

To decouple the Logging library from our domain, we have created a Logger interface that is implemented by the WinstonLogger class.

If we want to change the logging library, we only have to implement the Logger interface and update the dependecy on the LoggerModule.

NestJS Logger

NestJS uses a custom logger for bootstrap and internal logging. To use our logger, we need to create an adapter that implements the NestJS LoggerService interface. That is implemented in the NestjsLoggerServiceAdapter class.

We pass that adapter to the NestJS app on the main.ts file.

Correlation IDs

To manage correlation IDs, we use nestjs-cls library that implements a Local Storage. With that, we can isolate and share data on a request lifecycle.

The system reads the x-correlation-id HTTP header and stores it on the Local Storage. If the header is not present, the system generates a new UUID and stores it on the Local Storage.

Context Wrapper

To add custom data to all the logs, we use a wrapper LoggerContextWrapper.

That class is injected with a Transient scope. By that, we can get the caller class and add it to the logs.

Installation

  • Install dependencies

    yarn install

  • Copy file .env.example a .env

    cp .env.example .env

  • Start REST API

    yarn start:dev api

  • Test REST API

    curl -X GET http://localhost:3000

  • Test REST API with correlation ID

      curl -X GET http://localhost:3000 -H "x-correlation-id: 87815cc5-d0f2-41e5-a731-ac55bbb733e8"

To do

We will continue working on this project to add new features

PRs are welcome!

  • Add testing.