Docker & Containers

What is Docker?

Docker is a containerization platform that allows applications to run in isolated environments called containers. Instead of installing Apache Tomcat directly on the server, Docker packages Tomcat and the application together inside a container image. This ensures consistency, portability, and easier deployment across different environments.

Architecture Flow

Deploy Java Web Application with Docker

Aim: Deploy a Java Maven web application inside a Docker container instead of installing Apache Tomcat directly on the server.

Dockerfile

A Dockerfile is a text file containing instructions to build a Docker image. It defines the base image, copies application files, and sets the startup command.

FROM tomcat:10.1-jdk17

RUN rm -rf /usr/local/tomcat/webapps/*
COPY target/*.war /usr/local/tomcat/webapps/ROOT.war
EXPOSE 8080
CMD ["catalina.sh", "run"]

Step-by-Step Procedure

Step 1: Install Docker

sudo apt update
sudo apt install docker.io -y
sudo systemctl start docker
sudo systemctl enable docker

Step 2: Give Jenkins Permission to Use Docker

sudo usermod -aG docker jenkins
sudo systemctl restart jenkins

Step 3: Add Dockerfile to Project Repository

Create a file named Dockerfile in the root of your project and add the contents shown above.

Step 4: Update Jenkinsfile for Docker Deployment

Include pipeline stages to build WAR, build Docker image, remove old container, and run new container with port mapping.

Step 5: Open AWS Security Group Port

Allow inbound traffic on port 8090 in your AWS EC2 Security Group settings.

Step 6: Run Jenkins Pipeline

Click Build Now in Jenkins to build the Docker image and start the container.

Step 7: Access Application

# Open in browser:
http://<EC2-IP>:8090/

OS Container Management

Aim: Install Docker and create containers using different OS images — Ubuntu, Alpine, CentOS.

Download OS Images

docker pull ubuntu
docker pull alpine
docker pull centos
docker images

Run OS Containers

# Run Ubuntu container
docker run -it ubuntu /bin/bash

# Run Alpine Linux container (lightweight, ~5MB)
docker run -it alpine /bin/sh

# Run CentOS container
docker run -it centos /bin/bash

Manage Containers

# View running containers
docker ps

# View all containers (including stopped)
docker ps -a

# Stop a container
docker stop <container-id>

# Remove a container
docker rm <container-id>

# Remove an image
docker rmi <image-name>

Key Docker Commands