Here's a simple Node.js application that you can use as the source for your Docker-related questions.

Node.js App Example (for Dockerfile)

1. Application Structure

my-node-app/
│
├── Dockerfile           # You will write this based on the test
├── package.json         # Node.js dependencies
├── app.js               # Main application file
└── .dockerignore        # Ignore unnecessary files for Docker build

2. app.js (Main Node.js application)

This is a basic Express app that responds with a message when accessed at the root URL.

// app.js
const express = require('express');
const app = express();

const port = process.env.PORT || 3000;
const environment = process.env.NODE_ENV || 'production';

app.get('/', (req, res) => {
    res.send(`Hello, World! Running in ${environment} mode.`);
});

app.listen(port, () => {
    console.log(`App running on port ${port}`);
});

3. package.json (Dependencies and metadata)

This file defines the application’s dependencies, specifically express, which is the web framework used.

{
  "name": "my-node-app",
  "version": "1.0.0",
  "description": "A simple Node.js app",
  "main": "app.js",
  "scripts": {
    "start": "node app.js"
  },
  "dependencies": {
    "express": "^4.17.1"
  }
}

4. .dockerignore (Optional)

This file ensures that unnecessary files like node_modules or local configs are not included in the Docker build context, making the image smaller.

node_modules
npm-debug.log
.DS_Store

Sample Dockerfile

Here’s an example of a basic Dockerfile for this application:

# Step 1: Use official Node.js image as the base
FROM node:14

# Step 2: Set the working directory
WORKDIR /usr/src/app

# Step 3: Copy package.json and install dependencies
COPY package.json ./
RUN npm install

# Step 4: Copy the source code
COPY . .

# Step 5: Expose the port the app runs on
EXPOSE 3000

# Step 6: Set environment variables
ENV NODE_ENV=production

# Step 7: Define the command to run the application
CMD ["npm", "start"]

Running the App with Docker

1. Build the Docker image:

   docker build -t my-node-app .

2. Run the container:

   docker run -p 3000:3000 my-node-app

3. Visit http://localhost:3000, and you should see the message Hello, World! Running in production mode.

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You can use this application for the Dockerfile exercises in the test you create. It covers basic Docker concepts like installing dependencies, copying files, setting environment variables, and running the application.