**Course Title:** Mastering Development Environments **Section Title:** Containerization with Docker **Topic:** Build and run a simple application in a Docker container.(Lab topic) **Objective:** By the end of this lab, students will be able to build and run a simple application in a Docker container. This hands-on experience will help them understand the process of containerizing an application and running it in a Docker container. **Prerequisites:** Before starting this lab, students should have completed the following topics: - Introduction to containerization and its benefits - Installing Docker and setting up your first container - Creating Dockerfiles and using Docker Compose **Lab Overview:** In this lab, we will build and run a simple web application in a Docker container. The web application will be a Node.js application that serves a "Hello World" message. We will create a Dockerfile for the application, build a Docker image, and then run the application in a Docker container. **Step 1: Create a new directory for the project and initialize a new Node.js project** Create a new directory for the project, e.g., `hello-world-node`. Initialize a new Node.js project using npm (the package manager for Node.js) by running the following command in the terminal: ```bash npm init ``` Follow the prompts to complete the setup. **Step 2: Install the required dependencies** Install the required dependencies for the project by running the following command in the terminal: ```bash npm install express ``` **Step 3: Create a simple Node.js application** Create a new file called `app.js` and add the following code to it: ```javascript const express = require('express'); const app = express(); const port = 3000; app.get('/', (req, res) => { res.send('Hello World!'); }); app.listen(port, () => { console.log(`Example app listening on port ${port}`); }); ``` This code sets up a simple Express.js server that listens on port 3000 and serves a "Hello World!" message. **Step 4: Create a Dockerfile** Create a new file called `Dockerfile` and add the following code to it: ```dockerfile FROM node:14 WORKDIR /app COPY package*.json ./ RUN npm install COPY . . RUN npm run build EXPOSE 3000 CMD ["node", "app.js"] ``` This Dockerfile uses the official Node.js 14 image as its base, sets up a new directory for the application, installs the dependencies, copies the application code into the container, exposes port 3000, and sets the default command to run the Node.js application. **Step 5: Build the Docker image** Run the following command in the terminal to build the Docker image: ```bash docker build -t hello-world-node . ``` This command tells Docker to build a new image using the instructions in the Dockerfile. The `-t` flag specifies the name for the new image. **Step 6: Run the Docker container** Run the following command in the terminal to run the Docker container: ```bash docker run -p 3000:3000 hello-world-node ``` This command tells Docker to run a new container from the `hello-world-node` image and map port 3000 on the host machine to port 3000 in the container. **Step 7: Verify the application** Open a web browser and navigate to `http://localhost:3000` to verify that the application is working correctly. **Conclusion:** Congratulations! You have successfully built and run a simple Node.js application in a Docker container. This lab has covered the process of containerizing an application and running it in a Docker container. **What to do next:** - Experiment with different Dockerfiles and container configurations to understand the different options available. - Try containerizing a more complex application to see how Docker handles dependencies and other complexities. **External Resources:** - [Official Docker Documentation](https://docs.docker.com/) - [Official Node.js Documentation](https://nodejs.org/en/docs/) **Leave a comment or ask for help:** If you have any questions or need help with this lab, please leave a comment below.