{ "name": "simple-node-app", "version": "1.0.0", "description": "A simple Node.js app for Docker", "main": "index.js", "scripts": { "start": "node index.js" }, "dependencies": { "express": "^4.18.2" } } { "name": "simple-node-app", "version": "1.0.0", "description": "A simple Node.js app for Docker", "main": "index.js", "scripts": { "start": "node index.js" }, "dependencies": { "express": "^4.18.2" } } { "name": "simple-node-app", "version": "1.0.0", "description": "A simple Node.js app for Docker", "main": "index.js", "scripts": { "start": "node index.js" }, "dependencies": { "express": "^4.18.2" } } const express = require('express'); const app = express(); const PORT = 3000; app.get('/', (req, res) => { res.send('Hello from my Node.js app!'); }); app.listen(PORT, () => { console.log(`Server is running on http://localhost:${PORT}`); }); const express = require('express'); const app = express(); const PORT = 3000; app.get('/', (req, res) => { res.send('Hello from my Node.js app!'); }); app.listen(PORT, () => { console.log(`Server is running on http://localhost:${PORT}`); }); const express = require('express'); const app = express(); const PORT = 3000; app.get('/', (req, res) => { res.send('Hello from my Node.js app!'); }); app.listen(PORT, () => { console.log(`Server is running on http://localhost:${PORT}`); }); # Start from an official Node.js image. # The 'alpine' version is very small, which is great. FROM node:18-alpine # Create and set the working directory inside the container. WORKDIR /app # Copy package.json and package-lock.json first. # This helps Docker use its cache smartly. COPY package*.json ./ # Install the application dependencies inside the container. RUN npm install # Now, copy the rest of your application's source code. COPY . . # Tell Docker that the container listens on port 3000. EXPOSE 3000 # The command to run when the container starts. CMD ["node", "index.js"] # Start from an official Node.js image. # The 'alpine' version is very small, which is great. FROM node:18-alpine # Create and set the working directory inside the container. WORKDIR /app # Copy package.json and package-lock.json first. # This helps Docker use its cache smartly. COPY package*.json ./ # Install the application dependencies inside the container. RUN npm install # Now, copy the rest of your application's source code. COPY . . # Tell Docker that the container listens on port 3000. EXPOSE 3000 # The command to run when the container starts. CMD ["node", "index.js"] # Start from an official Node.js image. # The 'alpine' version is very small, which is great. FROM node:18-alpine # Create and set the working directory inside the container. WORKDIR /app # Copy package.json and package-lock.json first. # This helps Docker use its cache smartly. COPY package*.json ./ # Install the application dependencies inside the container. RUN npm install # Now, copy the rest of your application's source code. COPY . . # Tell Docker that the container listens on port 3000. EXPOSE 3000 # The command to run when the container starts. CMD ["node", "index.js"] # The -t flag lets you 'tag' or name your image. # The '.' at the end tells Docker to look for the Dockerfile in the current directory. docker build -t my-node-app . # The -t flag lets you 'tag' or name your image. # The '.' at the end tells Docker to look for the Dockerfile in the current directory. docker build -t my-node-app . # The -t flag lets you 'tag' or name your image. # The '.' at the end tells Docker to look for the Dockerfile in the current directory. docker build -t my-node-app . docker run -p 4000:3000 my-node-app docker run -p 4000:3000 my-node-app docker run -p 4000:3000 my-node-app node_modules npm-debug.log Dockerfile .dockerignore node_modules npm-debug.log Dockerfile .dockerignore node_modules npm-debug.log Dockerfile .dockerignore - Node.js: To run our simple application locally first. - Docker Desktop: The application that lets you build and run Docker containers. - Install the dependency: npm install - Start the server: node index.js - Dockerfile: This is a simple text file with a list of instructions. It's like a recipe for building our box. We will write this file ourselves. - Image: When you follow the recipe in the Dockerfile, you create an Image. An image is a blueprint. It's a saved, unchangeable package that contains our application and all its needs. - Container: A container is a running instance of an image. If the image is the blueprint, the container is the actual house built from that blueprint. You can create many containers from a single image. - FROM node:18-alpine: Every Docker image starts from a base image. Here, we start with an official image that already has Node.js version 18 installed on a minimal version of Linux called Alpine. - WORKDIR /app: This sets the default location inside the container for all subsequent commands. It's like running cd /app. - COPY package*.json ./: We copy our package files into the /app directory. We do this before copying our code. This is a smart trick. Docker builds in layers. If our code changes but package.json does not, Docker can reuse the npm install layer from a previous build, which saves a lot of time. - RUN npm install: This runs the command to install our dependencies inside the container. - COPY . .: Now we copy the rest of our files (like index.js) into the container. - EXPOSE 3000: This is like a piece of documentation. It tells Docker that our application inside the container will be using port 3000. It doesn't actually open the port to the outside world. - CMD ["node", "index.js"]: This is the final command that will be executed when the container starts. It runs our app. - docker run: The command to start a container. - -p 4000:3000: This is the port mapping. It connects port 4000 on your computer (the host) to port 3000 inside the container. Remember, EXPOSE 3000 only documented the port. This -p flag actually opens it up. - my-node-app: The name of the image we want to run. - Docker solves the "it works on my machine" problem by packaging your app and its environment into a single container. - A Dockerfile is a recipe for building a Docker Image. - A Container is a running instance of an Image. - Structure your Dockerfile to copy package.json and run npm install before you copy your source code. This makes your builds much faster. - Use the docker build command to create an image and docker run to start a container from it. - The -p flag is essential for connecting a port on your machine to a port inside the container, allowing you to access your app.