Spring Boot and Docker

Docker is a platform for developing, shipping, and running applications inside containers. This guide covers the key concepts and steps for using Docker with Spring Boot, including setting up Docker, creating a Dockerfile, building and running Docker images, and using Docker Compose.

Key Concepts of Spring Boot and Docker

• Docker: A platform for developing, shipping, and running applications inside containers.
• Dockerfile: A text file that contains instructions for building a Docker image.
• Docker Image: A lightweight, stand-alone, executable package that includes everything needed to run a piece of software.
• Docker Container: A runtime instance of a Docker image.
• Docker Compose: A tool for defining and running multi-container Docker applications.

Setting Up Docker

Follow these steps to set up Docker:

• Download and install Docker from the [Docker website](https://www.docker.com/products/docker-desktop).
• Verify the installation by running the following command:

$ docker --version

Creating a Dockerfile

Create a Dockerfile in the root directory of your Spring Boot project:

Example: Dockerfile

# Use an official OpenJDK runtime as a parent image
FROM openjdk:11-jre-slim

# Set the working directory in the container
WORKDIR /app

# Copy the JAR file into the container
COPY target/myapp.jar /app/myapp.jar

# Expose the port the app runs on
EXPOSE 8080

# Run the JAR file
ENTRYPOINT ["java", "-jar", "myapp.jar"]

Building and Running Docker Images

Build and run your Docker image using the following commands:

Building the Docker Image

$ docker build -t myapp:latest .

Running the Docker Container

$ docker run -p 8080:8080 myapp:latest

Using Docker Compose

Docker Compose is a tool for defining and running multi-container Docker applications. Create a docker-compose.yml file in the root directory of your project:

Example: docker-compose.yml

version: '3.8'
services:
  app:
    image: myapp:latest
    build: .
    ports:
      - "8080:8080"
    environment:
      SPRING_PROFILES_ACTIVE: docker
  db:
    image: postgres:latest
    environment:
      POSTGRES_DB: mydb
      POSTGRES_USER: user
      POSTGRES_PASSWORD: password
    ports:
      - "5432:5432"

Building and Running with Docker Compose

$ docker-compose up --build

Example: Using Environment Variables in Docker

You can pass environment variables to your Spring Boot application using Docker:

Example: application.properties

spring.datasource.url=jdbc:postgresql://db:5432/mydb
spring.datasource.username=${POSTGRES_USER}
spring.datasource.password=${POSTGRES_PASSWORD}

Running the Docker Container with Environment Variables

$ docker run -p 8080:8080 -e POSTGRES_USER=user -e POSTGRES_PASSWORD=password myapp:latest

Key Points

Conclusion

Docker and Spring Boot provide a powerful combination for developing, shipping, and running applications. By understanding and using the capabilities of Docker with Spring Boot, developers can create scalable, portable, and maintainable applications efficiently. Happy coding!