আজকের ক্লাসের কাজ হচ্ছে আমাদের backend application টাকে আমরা dockerize করব …

docker is just a virtualize environment … right ? same as before we will start with ubuntu as our base image …

so let’s start …

Step 1 : Start with `Ubuntu` base image

Run the following command. Make sure you ran the command from your repository base location.

# docker run -it -v $(pwd):/app -p 8080:8080 ubuntu
docker run -it -v $(pwd):/app --network=host ubuntu

Ok. After we run above command, our terminal will be attached to container’s terminal. We have our repository linked at /app location inside the container and we also have exposed container’s 8080 port and mapped the port to host’s 8080 port.

Step 2 : Install dependencies

Update ubuntu’s apt repository and install all the dependencies that we need to run our backend

root@a21d865e2aa3:/# apt update && apt install -y openjdk-17-jdk

Confirm Java 17 is installed

root@a21d865e2aa3:/# java --version 
openjdk 17.0.16 2025-07-15
OpenJDK Runtime Environment (build 17.0.16+8-Ubuntu-0ubuntu124.04.1)
OpenJDK 64-Bit Server VM (build 17.0.16+8-Ubuntu-0ubuntu124.04.1, mixed mode, sharing)

openjdk-17-jdk also installs the jre. So we don’t need to think about the runtime. Now we need to install another dependency maven

root@a21d865e2aa3:/# apt install -y maven

With installing maven, all our dependencies are now installed.

Step 3 : Building the application

root@a21d865e2aa3:/# cd /app/
root@a21d865e2aa3:/app# mvn package -Dmaven.test.skip

As we might have some failed test cases, we have skipped the test cases with -Dmaven.test.skip

We now have a runnable jar file

root@ip-172-31-9-208:/app# ls -al target/devops-demo-0.0.1-SNAPSHOT.jar
-rw-r--r-- 1 root root 63072155 Oct 12 14:49 target/devops-demo-0.0.1-SNAPSHOT.jar

Step 4: Run the application

java -jar target/devops-demo-0.0.1-SNAPSHOT.jar

Automating Steps with `Dockerfile`

Writing `Dockerfile`

Let’s recap what we did manually to run our application inside a container.

Step 1: We started with a base iamge Ubuntu Step 2: We have installed dependencies Step 3: We built our application Step 4: We ran our application

So, with Dockerfile we will automate the steps. Let’s open a file named Dockerfile in our repository

# Step 1: We are defining our base image
FROM ubuntu:22.04                                          

# Copying our application in /app directory
COPY ./ /app

# Fix our working directory to our app directory where we copied our source code
WORKDIR /app                                              

# Tells docker not to ask tzdata and other interactive questions
ARG DEBIAN_FRONTEND=noninteractive 

# Step 2: Installing dependencies
RUN apt update && apt -y install openjdk-17-jdk maven     

# Step 3: Building Application
RUN mvn package -Dmaven.test.skip

# Step 4: Run the application
ENTRYPOINT ["java", "-jar", "target/devops-demo-0.0.1-SNAPSHOT.jar"]

Building image from `Dockerfile`

Our Dockerfile is ready. Now it’s time to build the image from Dockerfile

docker build -t rafaftahsin/devops-demo-backend:v4 .

Run application

With docker image being built, let’s run it

docker run --network=host rafaftahsin/devops-demo-backend:v4

docker run with env file

change host network

docker compose

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Step 1 : Start with Ubuntu base image