What is Docker?

Docker is a platform for developing, delivering, and running applications in isolated environments called containers. Docker containers combine application code with all its dependencies (libraries, frameworks, configurations, etc.), providing a consistent environment for execution on any system with Docker installed.

Key concepts:

• Docker Image: An immutable, executable package containing everything needed to run an application. It serves as a template for creating containers.

• Docker Container: A running instance of an image. An isolated process that operates with its own set of resources (file system, network, memory).

• Dockerfile: A text file containing instructions for building a Docker image.

# Using a base Python image
FROM python:3.9-slim

# Installing dependencies
RUN pip install requests

# Copying application source code
COPY app.py /app/

# Setting working directory
WORKDIR /app

# Defining command to run the application
CMD ["python", "app.py"]

• Docker Hub: A cloud registry for storing and sharing Docker images.

Advantages of Docker:

• Portability: Containers work the same on any system with Docker installed, eliminating "it works on my machine" problems.
• Isolation: Each container is isolated from others and from the host system, enhancing security and stability.
• Reproducibility: Images guarantee that the runtime environment will always be the same.
• Fast deployment: Containers start faster than virtual machines.
• Resource optimization: Containers use shared OS kernel resources, consuming fewer resources compared to virtual machines.

Docker is widely used in CI/CD (Continuous Integration/Continuous Deployment) processes for automated building, testing, and deploying applications.