Unable to debug a nodejs app inside of docker - node.js

Question

I am trying my hands on debugging a Nodejs app from inside of Docker using Nodemon.
I can debug my app with Nodemon without Docker using Visual Studio Code's Auto Attach feature.
But when I build my docker image and start the container via npm run dev:docker:debug I get following log but debugger is not attached. It might be something with the volume but I am not able to figure it out...
Successfully built 857d9da57565
Successfully tagged app:dev
Creating docker_app_1 ... done
Attaching to docker_app_1
app_1 |
app_1 | > app#1.0.0 dev:debug /usr/src/app
app_1 | > nodemon --config nodemon.json --env=development
app_1 |
app_1 | [nodemon] 2.0.2
app_1 | [nodemon] to restart at any time, enter `rs`
app_1 | [nodemon] watching dir(s): src/**/*
app_1 | [nodemon] watching extensions: ts
app_1 | [nodemon] starting `cross-env NODE_OPTIONS='--inspect=0.0.0.0:5858' ts-node -r tsconfig-paths/register ./src --env=development`
app_1 | Debugger listening on ws://0.0.0.0:5858/k3h42h4-h49d-4f00-adj877-60f6731548787
app_1 | For help, see: https://nodejs.org/en/docs/inspector
app_1 | Service started at ports:3000
Folder structure
App
|-- docker
| |-- docker-compose.yml
| |-- Dockerfile
| `-- .dockerignore
|-- nodemon.json
|-- package.json
|-- tsconfig.json
|-- tslint.json
`-- src
`-- index.ts
index.ts
import express, { Request, Response } from "express";
const app = express();
const port = process.env.PORT || 3000; // default port to listen
// define a route handler for the default home page
app.get("/", (req: Request, res: Response) => {
res.send("Hello worlds!");
});
// start the Express server
app.listen(port, () => {
console.log(`Service started at ports:${port}`);
});
docker-compose.yml
# docker-compose.yml
version: "3"
services:
app:
image: app:dev
build:
context: ../
dockerfile: ./docker/Dockerfile
ports:
- 3000:3000
volumes:
- ../src:/usr/src/app/src/
Dockerfile
FROM node:12-slim
WORKDIR /usr/src/app
COPY package*.json ./
RUN npm install
COPY . ./
CMD [ "npm", "run", "dev:debug" ]
package.json
{
"name": "app",
"version": "1.0.0",
"description": "API to receive data",
"author": "Nikhil Gupta",
"main": "./dist/index.js",
"scripts": {
"dev:debug": "nodemon --config nodemon.json --env=development",
"dev:docker:debug": "docker-compose -f ./docker/docker-compose.yml up --build"
},
"dependencies": {
"cross-env": "^6.0.3",
"express": "^4.17.1",
"ts-node": "^8.5.4",
"tsconfig-paths": "^3.9.0",
"tslib": "^1.10.0"
},
"devDependencies": {
"#types/express": "^4.17.2",
"#types/node": "^12.12.21",
"nodemon": "^2.0.2",
"tslint": "^5.20.1",
"typescript": "^3.7.4"
}
}
nodemon.json
{
"watch": ["src"],
"ext": "ts",
"ignore": ["src/public"],
"inspect": true,
"exec": "cross-env NODE_OPTIONS='--inspect=0.0.0.0:5858' ts-node -r tsconfig-paths/register ./src"
}

Answer 1

Since the debugger is listening on port 5858 inside the container, you need to bind it to a port on the host machine if you want to connect to it from outside the container similar to how you have done for port 3000 in your compose file.
# docker-compose.yml
version: "3"
services:
app:
image: app:dev
build:
context: ../
dockerfile: ./docker/Dockerfile
ports:
- 3000:3000
- 5858:5858
volumes:
- ../src:/usr/src/app/src/

Answer 2

As mentioned in the comments by #ykit9 I did following
1) Added port 5858 into my docker-compose.yml
# docker-compose.yml
version: "3"
services:
app:
image: app:dev
build:
context: ../
dockerfile: ./docker/Dockerfile
ports:
- 3000:3000
- 5858:5858
volumes:
- ../src:/usr/src/app/src/
2) Added following configuration in VS Code's launch.json file.
{
"type": "node",
"request": "attach",
"name": "Attach to Docker",
"protocol": "auto",
"port": 5858,
"restart": true,
"localRoot": "${workspaceFolder}/src",
"remoteRoot": "/usr/src/app/src"
}