What is Docker?

Docker is a platform for developing, shipping, and running applications in containers. A container is a lightweight, isolated, executable package that includes everything needed to run an application: code, system libraries, dependencies, and configuration.

Key concepts of Docker:

• Image: A read-only template with instructions for creating a container. Images are built in layers.
• Container: An executable instance of an image. Containers are isolated and can be easily created, started, stopped, and removed.
• Dockerfile: A script containing a set of instructions for automatically building a Docker image.
• Docker Hub (or other registries): A repository for storing and sharing Docker images.

Advantages of using Docker:

• Portability: Applications run the same way in any environment with Docker installed.
• Isolation: Containers isolate applications from each other and from the host system.
• Reproducibility: Building images from a Dockerfile guarantees the same environment every time.
• Fast deployment: Containers start very quickly compared to virtual machines.
• Dependency management: All dependencies are packaged inside the container.

Example of a Dockerfile:

# Use the OpenJDK base image
FROM openjdk:11-jdk-slim

# Set the working directory inside the container
WORKDIR /app

# Copy the application JAR file into the container
COPY target/my-java-app.jar /app/my-java-app.jar

# Define the command to run the application
CMD ["java", "-jar", "my-java-app.jar"]