Docker Crash Course Notes

Introduction to Docker

• This crash course covers all main concepts of Docker.
• Aimed at engineers needing fast hands-on experience.
• Topics include:
  • Understanding what Docker is and why it was created.
  • Installation and practical usage of Docker.

What is Docker?

• Docker is a virtualization software that simplifies the development and deployment of applications by:
  • Packaging applications into containers that include code, libraries, dependencies, runtime, and environment configurations.
• Benefits of Docker include:
  • Easier sharing and distribution of applications.
  • Standardization of development environments.
  • Speed and efficiency compared to traditional installation methods.

Problems Solved by Docker

Pre-Docker Development Challenges

• Teams had to install all services (e.g., databases, caching systems) directly on their OS.
• Each developer's environment varied based on OS, leading to inconsistent setups.
• High potential for errors and tedious setup processes.

Docker's Solution

• Containers allow developers to run packaged services in isolated environments without OS conflicts.
• Standardized Docker commands make setup consistent across environments.
• Enables running multiple versions of an application without conflict.

Application Deployment with Docker

Traditional Deployment Challenges

• Developers hand off application artifacts with installation instructions to operations teams.
• High potential for configuration errors and miscommunication.

Docker's Improved Process

• Applications, dependencies, and configurations are packaged together in a Docker container.
• Operations teams only need to run Docker commands to set up and run applications, reducing complexity.

Virtual Machines vs. Docker

Core Differences

• Docker:

  • Virtualizes the applications layer only, sharing the host OS kernel.
  • Container images are smaller and start faster (milliseconds).
  • Limited to the host OS kernel.

• Virtual Machines:

  • Virtualizes the entire OS with its own kernel.
  • Image sizes are larger (gigabytes) and start slower (minutes).
  • Can run different OS types on the host.

Installation of Docker

• Download Docker Desktop from the official site and follow the installation guide.
• Docker Desktop includes:
  • Docker engine
  • Command line interface (CLI)
  • Graphical user interface (GUI)

Docker Images and Containers

• Docker Images:

  • Application packages containing code, libraries, and environment configurations.
  • Retrieved from Docker Hub (public registry).

• Docker Containers:

  • Running instances of Docker images.
  • Multiple containers can run from the same image.

Docker Registries

• Docker Hub:
  • Largest public registry for Docker images.
  • Offers official images created by technology vendors or the community.
• Private Registries:
  • For storing proprietary application images (e.g., AWS ECR).

Image Versioning

• Images are versioned using tags (e.g., latest, specific version).
• Recommended to specify a version when pulling images.

Creating Custom Docker Images

• Use a Dockerfile to define how to build a custom image.
• Common Dockerfile commands:
  • FROM: Specifies the base image.
  • COPY: Copies files into the container.
  • RUN: Executes commands (e.g., installing dependencies).
  • CMD: Defines the command to run when the container starts.

Running Containers

• Use docker run command to start containers from images.
• Port binding to access container applications from a local machine.

Docker in Software Development Lifecycle

• Typical Workflow:
  1. Develop application locally using Docker containers.
  2. Push images to a private repository after building them with CI tools.
  3. Deploy containers from the repository on development or production servers.
• Docker streamlines the process, ensuring consistent environments from development to deployment.

Conclusion

• Key concepts covered: images, containers, Dockerfile creation, and deployment processes.
• Further learning opportunities include Docker Compose, Docker Volumes, and integration with CI/CD pipelines.