Docker: An Introduction

• Docker: An Introduction
  • What is Docker?
  • Deployments
    • Before Linux Containers
    • With Linux Containers
  • How Does Docker Operate?
  • VMs vs Containers
  • Docker Installation
    • Docker Desktop
      • Key Features
      • Advantages
    • Minikube
      • Key Features
      • Advantages
  • Docker Desktop vs. Minikube: The Showdown
  • References
    • Further Reading
    • Videos

What is Docker?

Docker is an open-source tool that facilitates the automation of deploying applications inside lightweight, portable, and self-sufficient containers.

Main Features:

• Containerization: Docker wraps software with all its dependencies into a standardized unit.
• Portability: Once containerized, the software can be run consistently across various environments.
• Microservices: Docker aids in breaking down applications into smaller, manageable pieces which can be developed, deployed, and scaled individually.

Deployments

• Isolation is the key to running applications securely and efficiently.
• Virtual Machines (VMs) and Linux Containers are two technologies that enable this isolation.

Before Linux Containers

In the pre-container era, the predominant model for running applications was to use physical servers or virtual machines (VMs).

• Physical Servers:
  • Initially, applications were deployed directly on physical servers.
  • This approach provided good isolation
  • Inefficient, as you couldn’t fully utilize a server’s resources if your application didn’t need them
  • Not Scalable as, running multiple applications on a single server could lead to dependency conflicts and other issues.
• Virtual Machines:
  • To improve resource utilization with compromising on isolation, virtual machines (VMs) were introduced
  • A VM simulates a physical computer, running an entire operating system (OS) and applications on top of a hypervisor
  • VMs provide good isolation, but they have significant overhead because each VM runs a full OS which results in wasted resources and slower startup times.

With Linux Containers

• We package applications with their dependencies into a standardized unit for software development, called a container image.
• These images bundle the application and all its dependencies, including libraries and other binaries, and ship them as one package.
• Containers are instances of these images that can be run using a container runtime.
• Containers are isolated from one another and share single host OS kernel.
• They can communicate with each other through well-defined channels.
• Efficient - Containers are lightweight and start quickly, fully utilizing the host system’s resources.
• Scalable - Containers can be easily scaled up or down based on the application’s needs.
• Portable - Containers can be run consistently across various environments.
• Standardization - Containers are deployed in a standard fashion, irrespective of the underlying infrastructure or the application’s complexity or technology stack.

How Does Docker Operate?

At the heart of Docker’s prowess lie several Linux features that enable its unique approach to virtualization:

1. Control Groups (cgroups): They control resources ensuring Docker containers consume only what they’re allotted.
2. Namespaces: It offers isolation between containers. Each container feels like it’s the sole process holder.
3. Chroot: It’s a process to change the root directory for a process, allowing Docker to provide isolated file systems to containers.
4. Union File Systems (UnionFS): Allows Docker to create layers, making image creation and container spin-up efficient.
5. Security Modules (e.g., SELinux, AppArmor): They ensure containers cannot negatively impact the host system.

VMs vs Containers

• Containers and virtual machines are very similar resource virtualization technologies
• Virtualization is the process in which a system singular resource like RAM, CPU, Disk, or Networking can be ‘virtualized’ and represented as multiple resources.
• The key differentiator between containers and virtual machines:
  • Virtual machines virtualize an entire machine down to the hardware layers
  • Containers only virtualize software layers above the operating system level

Attributes	Virtual Machines (VMs)	Containers
System Overhead	VMs have a full OS copy, creating higher overhead.	With shared host kernel, containers have lesser overhead.
Boot-Up Time	VMs boot slower due to a complete OS initialization.	Containers boast near-instantaneous boot times.
Performance	VMs offer good, but sometimes inefficient performance.	Containers, being lightweight, ensure enhanced performance.
Isolation	VMs provide stronger isolation since they run separate OS instances.	Containers offer good isolation but share the host’s kernel.
Portability	VMs can suffer from host-guest OS dependency issues.	Docker ensures high portability across any Docker-supporting system.
Security	VMs offer great security due to robust resource isolation.	Containers, while generally secure, might be vulnerable at kernel-level.
Disk Space	VMs require more space (OS + app).	Containers only house the app and its dependencies, saving space.
Best Use Cases	Suited for tasks needing full OS resources.	Ideal for microservices as they scale components effectively.

Docker Installation

2 most popular ways to install Docker locally:

• Docker Desktop (Recommended for Windows & Mac)
• Minikube

Docker Desktop

Docker Desktop is an easy-to-use graphical user interface (GUI) tool that provides Docker and Kubernetes functionalities for both macOS and Windows users.

Key Features

• Integrated Development Environment: It includes a full development environment, including Docker CLI, Docker Compose, and Docker Notary.
• Built-in Kubernetes: Comes with a single-node Kubernetes cluster built-in, allowing users to deploy Kubernetes-based applications locally.
• File Sharing: Seamless sharing of files between the host and containers.
• GUI-based Management: Offers a user-friendly interface to manage images, containers, and networks.

Advantages

• Easy Setup: Streamlined installation and setup process for both Docker and Kubernetes.
• Developer-Friendly: Offers integration with IDEs like Visual Studio Code.
• Network Integration: Containers can be accessed using localhost on macOS and Windows, thanks to the underlying hypervisor’s network integration.

Minikube

Minikube is an open-source tool specifically designed to run a local Kubernetes cluster on your local machine, primarily for the sake of learning and development.

Key Features

• Single-Node Cluster: Provides a single-node Kubernetes cluster, great for testing and development.
• Multiple Hypervisors: Supports various hypervisors, including VirtualBox, VMware Fusion, and others.
• Add-ons: Supports various Kubernetes add-ons, extending its features for development.

Advantages

• Pure Kubernetes Experience: Offers a closer resemblance to a real-world Kubernetes cluster, allowing users to learn raw Kubernetes.
• Flexible: Due to its compatibility with multiple hypervisors, it can be used across many platforms.
• Customizable: Minikube’s CLI, minikube, has numerous commands and flags, allowing users to customize and configure their local cluster.

Docker Desktop vs. Minikube: The Showdown

Criteria	Docker Desktop	Minikube
Primary Use Case	Containerization with Docker, and Kubernetes development.	Purely Kubernetes learning and development.
Platform	Windows and macOS.	Windows, macOS, and Linux.
Hypervisor Dependency	Uses underlying platform’s hypervisor.	Works with multiple hypervisors.
Networking	localhost access on macOS and Windows.	IP-based access depending on the hypervisor.
Ease of Use	GUI and CLI options. Streamlined setup.	More configuration might be required. Pure CLI tool.
Customizability	Limited compared to Minikube.	High degree of customization using minikube commands.

References

Further Reading

• Docker Explained: A Beginner’s Guide
• Quick Dive into Docker
• VM vs Containers

Videos

• Physical Containers vs Virtual Machines vs Containers
• Docker 101