Debugging with Docker Containers

Debugging with Docker Containers

More information about debugging Node.js applications within Docker containers can be found at Debug Node.js within a container.

Lets do hands-on on debugging with example using nestcli

creating app using nestcli

The Nest CLI is a command-line interface tool that helps you to initialize, develop, and maintain your Nest applications. It assists in multiple ways, including scaffolding the project, serving it in development mode, and building and bundling the application for production distribution. It embodies best-practice architectural patterns to encourage well-structured apps.


Note: In this guide we describe using npm to install packages, including the Nest CLI. Other package managers may be used at your discretion. With npm, you have several options available for managing how your OS command line resolves the location of the nest CLI binary file. Here, we describe installing the nest binary globally using the -g option. This provides a measure of convenience, and is the approach we assume throughout the documentation. Note that installing anynpm package globally leaves the responsibility of ensuring they're running the correct version up to the user. It also means that if you have different projects, each will run the same version of the CLI. A reasonable alternative is to use the npx program (or similar features with other package managers) to ensure that you run a managed version of the Nest CLI. We recommend you consult the npx documentation and/or your DevOps support staff for more information.

Install the CLI globally using the npm install -g command (see the Note above for details about global installs).

$ npm install -g @nestjs/cli

Basic workflow Once installed, you can invoke CLI commands directly from your OS command line through the nest executable. See the available nest commands by entering the following:

$ nest new my-nest-project
$ cd my-nest-project
$ npm run start:dev

In your browser, open http://localhost:3000 to see the new application running. The app will automatically recompile and reload when you change any of the source files.

Now we have node js application running on 3000 Port locally you can pick existing nestjs application also

now lets setup debugging with nodemon and docker

Update Package JSON with debug script start:debug script

  "name": "app",
  "version": "1.0.0",
  "description": "app",
  "scripts": {
    "start": "ts-node ./src/main.ts",
    "start:debug": "nodemon",
    "start:prod": "node ./dist/src/main.js",

As we are running using nodemon we need nodemon.json file to run application in debug Mode --inspect= will help us to attach debugger on process

  "watch": ["src"],
  "ext": "ts",
  "ignore": ["src/**/*.spec.ts","test/**/*.ts"],
  "exec": "node --inspect= -r ts-node/register ./src/main.ts"

This works fine on Local but what about when we run application on docker container and we need debugging enabled Please follow these steps to perfor debuggong on container

Create your dockerfile

FROM node:12-buster-slim
COPY package.json package-lock.json /app/
RUN npm install && \
    rm -rf /tmp/* /var/tmp/*
COPY . /app
RUN npm run build
CMD npm run start:prod

Another file is docker-compose file to run this container using docker-compose up command, Here command in compose file is command: npm run start:debug which will help us triggering container debug

version: "3"
    build: .
    command: npm run start:debug
      - .:/app

Added file docker-compose.override.yml which is exposting container and debug port mapping 5858 and 3000 PORTs

version: "3"
    command: npm run start:debug
      - 3015:3000
      - 5858:5858

Now we can run docker-compose up to run application and container is exposting 3015 and 5858 port, we can use 5858 for container debugging

Debugging can be configured on VSCode only using .vscode folder and launch.json file your launch.json in .vscode folder

  • add same port exposed by container 5858
  • keep address "address": "",
  • request should be attach as we are attachinh debugger
  • "localRoot": "${workspaceFolder}" as you have open project in vscode and not whole workspace
  "configurations": [
      "name": "Docker: Attach to Node",
      "type": "node",
      "request": "attach",
      "port": 5858,
      "address": "",
      "localRoot": "${workspaceFolder}",
      "remoteRoot": "/",
      "protocol": "inspector"

Running all things together

  • run application using docker-compose up once we see applicarion running perform below setp -
  • go to debug tool in vscode and click on docker-attach it can be done from vscode UI debug console

Once we see applicaion running we should be able to attach debugger from vscode and then we can debug our controller or services

node_1  | [Tue Dec 08 05:48:39 2020] [info] PmApprovalActionsController {/test}:
node_1  | [Tue Dec 08 05:48:39 2020] [info] Mapped {/test/test-sheet, POST} route
node_1  | [Tue Dec 08 05:48:40 2020] [info] Nest application successfully started
node_1  | Debugger attached.

Now you can add debug Point and Hit APIs from Postman and debug your controllers and services