Start with an existing Node.js application or create a new one

> express my-express-app
> cd my-express-app
> npm install
> code .

Add Docker files to the application

Press F1 to open the command palette and select the Docker: Add Docker Files to Workspace command

Select Node.js

Select either Yes or No to include Docker Compose files. (Neither option affects whether you can debug the application in VS Code.)

Enter the port on which the application listens (e.g. typically 3000)

The Docker extension will add, at minimum, a .dockerignore and Dockerfile files. It will also add tasks for building and running the application within a Docker container, as well as a launch configuration for debugging the application.

The Docker extension infers the entry point of the Docker container--that is, the command line for starting the application in a debug mode within the Docker container--via properties of package.json. The extension will first look for the start script in the scripts object; if found and, if it starts with a node or nodejs command, it will be used to build the command line for starting the application in debug mode. If not found or, if not a recognized node command, the main property in the package.json will be used. If neither is found or recognized, then the user will need to set the dockerRun.command property of the docker-run task used to start the Docker container.

Some Node.js application frameworks include CLIs for managing the application and used to start the application in the start script, which obscure the underlying node commands. In these cases, the Docker extension cannot infer the start command and the user must configure it manually.

{
    "tasks": [
        {
            "type": "docker-run",
            "label": "docker-run: debug",
            "dependsOn": [
                "docker-build"
            ],
            "dockerRun": {
                "command": "nest start --debug 0.0.0.0:9229",
            },
            "node": {
                "enableDebugging": true
            }
        }
    ]
}

{
    "tasks": [
        {
            "type": "docker-run",
            "label": "docker-run: debug",
            "dependsOn": [
                "docker-build"
            ],
            "dockerRun": {
                "command": "node --inspect=0.0.0.0:9229 main.js",
            },
            "node": {
                "enableDebugging": true
            }
        }
    ]
}

The Docker extension can automatically launch the browser to the entry point of the application after it has started in the debugger. (This feature is enabled by default and configured via the dockerServerReadyAction object of the debug configuration in launch.json.) This feature depends on the application writing its logs to the debug console of the attached debugger. However, not all logging frameworks will write to the debug console, even when configured to use a console-based logger (as some "console" loggers will actually bypass the console and write directly to stdout).

The solution varies depending on the logging framework, but it generally requires creating/adding a logger that actually writes to the console.

By default, Express.js uses the debug logging module, which can bypass the console. This can be resolved by explicitly binding the log function to the console's debug() method.

var app = require('../app');
var debug = require('debug')('my-express-app:server');
var http = require('http');

debug.log = console.debug.bind(console);

Also note that the debug logger will not write logs unless enabled via the DEBUG environment variable, which can be set in the docker-run task. (This environment variable is set to * by default when Docker files are added to the application.)

{
    "tasks": [
        {
            "type": "docker-run",
            "label": "docker-run: debug",
            "dependsOn": [
                "docker-build"
            ],
            "dockerRun": {
                "env": {
                    "DEBUG": "*"
                }
            },
            "node": {
                "enableDebugging": true
            }
        }
    ]
}