Day 29: Hands-On with Docker – Build Your First Java Project Container from Scratch Using Dockerfile.

Today, we dive into one of the core concepts of Docker: understanding what a Dockerfile, Docker Image, and Container are, along with a real-life analogy (Maggi 😋) and practical demo to make things super easy to follow.

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🔹 What is a Dockerfile, Image, and Container?

Let’s break it down:

• Dockerfile: Think of it as a set of instructions written in a script format. It defines the environment, tools, dependencies, and everything needed to run your application.
  (Like a recipe to cook something.)

• Docker Image: Once a Dockerfile is executed, it generates an image. This image is like a blueprint of your environment and application.
  (Like the Maggi masala packet, already prepped and ready to use.)

• Docker Container: When you run a Docker image, you create a container — a live, running instance of the image.
  (Like actually cooking the Maggi and serving it in a bowl 🍜.)

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🔸 Real-Life Example: Let’s Understand with Maggi 🍲

Just like we cook Maggi:

1. We take a pot (this is our runtime environment).

2. Follow the recipe — first add water, then noodles, then masala, etc. (This is the Dockerfile.)

3. The complete cooked Maggi is like our Docker Image.

4. Now every time you use this masala and recipe, you can create multiple bowls of Maggi — which are the containers.

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🔹 Practical Demo: Let's Get Started

1️⃣ Step 1: Login to Docker Hub

Before we can pull or push any Docker images, we need to log into Docker Hub.

bashCopyEditdocker login

🔐 Note: Sometimes the password doesn’t work. In that case, go to your Docker Hub account settings and create a personal access token to use instead of your password.

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2️⃣ Step 2: Pull the hello-world Image

Let’s start with a very basic Docker image:

bashCopyEditdocker pull hello-world

Now check if the image was pulled successfully:

bashCopyEditdocker images

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3️⃣ Step 3: Run the Image to Create a Container

Now run the pulled image:

bashCopyEditdocker run hello-world

This will create and run a container based on the hello-world image.

// Screenshot: Output of docker run hello-world

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4️⃣ Step 4: Try a Server Image - MySQL

Let’s now pull a server-based image like MySQL:

bashCopyEditdocker pull mysql

Again, confirm it:

bashCopyEditdocker images

To run the MySQL image (which requires a root password), use:

bashCopyEditdocker run -d -e MYSQL_ROOT_PASSWORD=root mysql

Then check if the container is running:

bashCopyEditdocker ps

// Screenshot: Output of docker ps

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🛠️ Now Let’s Create Our Own Dockerfile and Build a Container

We’ll now take a sample Java project from GitHub and create a Docker container for it.

5️⃣ Step 5: Setup Project Folder

First, create a new directory:

bashCopyEditmkdir java-project
cd java-project

Clone a Java project:

bashCopyEditgit clone <your-java-project-link>

// Screenshot: Project cloned from GitHub

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6️⃣ Step 6: Create a Dockerfile

Inside the project folder, create a Dockerfile:

bashCopyEditvim Dockerfile

Example Dockerfile content:

DockerfileCopyEditFROM openjdk:17
COPY . /usr/src/myapp
WORKDIR /usr/src/myapp
RUN javac Main.java
CMD ["java", "Main"]

This Dockerfile sets up a basic Java environment and tells Docker how to run your project.

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7️⃣ Step 7: Build the Docker Image

Now let’s build the Docker image using our Dockerfile:

bashCopyEditdocker build -t java-app .

// Screenshot: Docker image built

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8️⃣ Step 8: Run the Container

Once the image is built, run it:

bashCopyEditdocker run java-app

This will execute your Java project inside a Docker container.

// Screenshot: Output of docker run java-app