Docker Overview

Introduction

• Docker: essential for software engineers, full-stack developers, backend developers, and DevOps engineers.

Background

• First encountered Docker when working with VMs.
• Docker is essential to solve common development process issues.
• Key topics: Docker's necessity, Docker vs. VMs, basic Docker commands.

Key Problems in Development Without Docker

1. Environment Reproduction: Issues arise when replicating local environments across different machines.
   • Example: Setting up same environment on different OS (e.g., Windows to Mac) with different versions of dependencies.
2. Manual Errors: Setting up dependencies manually can lead to errors.
3. Version Specificity: Some applications require specific versions to run (e.g., NodeJS 16 only).
4. System Compatibility: Commands or dependencies may not work the same across different OS.
5. Large Development Teams: Difficult to ensure the same setup across all developer systems.
6. Production Servers: Same environment needs to be replicated on production servers, which introduces more issues.

Docker Solution

• Helps to package applications with their dependencies in containers.
• Containers are portable and lightweight.
• No need to worry about OS differences when sharing these containers.

Concepts of Docker

1. Containers: Self-contained units with application code and dependencies.
   • Portable across different machines (macOS, Windows, Linux, etc.).
   • Lightweight, easy to build, update, destroy, and share.
2. Docker Platform: Service to build, destroy, and manage containers.
   • Containers can be shared easily among team members and production servers.
3. Docker Desktop: GUI tool to manage Docker images and containers.
4. Docker Hub: Repository for Docker images, similar to GitHub for code.
   • Docker images can be pulled from Docker Hub using docker pull command.

Practical Docker Usage

1. Basic Commands:
   • docker pull <image_name>: Pulls a Docker image from Docker Hub.
   • docker run <image_name>: Runs a Docker image, creating a container.
   • docker stop <container_id>: Stops a running container.
2. Example: Running hello-world and ubuntu images as containers.
   • Pulling and running a hello-world image.
   • Pulling and running an ubuntu image in interactive mode for executing commands inside the container.

Containers vs Virtual Machines

1. Docker Containers:
   • Use the host operating system's kernel.
   • Only virtualize the application layer.
   • Lightweight and faster.
   • Size usually in MBs.
2. Virtual Machines:
   • Have their own operating system kernel.
   • Virtualize both application and OS layers.
   • Heavier and slower.
   • Size usually in GBs.
   • VM Hypervisors provide full OS compatibility.

Common Misconceptions

• Docker Desktop adds a lightweight hypervisor to facilitate lightweight system usage.
• Docker is not a replacement for VMs; both serve different purposes.

Conclusion

• Docker simplifies the development environment setup.
• Facilitates sharing and running applications consistently across various environments.
• Essential for modern software development practices, especially in large teams and production deployments.