Understanding Containers: From Virtual Machines to Modern Containerization

Introduction

Containers represent a significant evolution in server virtualization technology. To understand containers properly, we first need to understand the progression from physical servers to virtual machines, and then to containers.

The Evolution of Server Infrastructure

1. Physical Servers

• Organizations traditionally used physical servers (from vendors like IBM or HP)

• Major challenge: Resources (CPU, RAM, Hardware) were often underutilized

• Cost inefficient as organizations paid for unused resources

• High maintenance overhead requiring dedicated system administrators

2. Virtual Machines (VMs)

• Introduced virtualization using hypervisors

• Allows creation of multiple virtual servers on a single physical server

• Each VM has its own complete operating system

• Benefits:

  • Better resource utilization than physical servers

  • Secure isolation due to individual operating systems

  • Logical separation between applications

• Limitations:

  • Still often underutilize resources

  • Each VM requires significant resources due to full OS

  • Large snapshot sizes (typically 1-3GB)

3. Containers

Containers solve some of the limitations of virtual machines while bringing their own advantages and trade-offs.

Key Characteristics of Containers:

• Lightweight nature (typically 100-500MB)

• Don't include a full operating system

• Share resources with the host OS

• Easy to ship and transfer

• Quick to start and stop

Container Architecture

Components of a Container

A container is a package that includes:

1. The application itself

2. Application libraries and dependencies

3. Minimal system dependencies

4. Base image with minimal OS components

Two Models of Container Deployment

Model 1: Direct on Physical Server

• Physical Server → OS → Containerization Platform → Containers

• Less common today due to maintenance overhead

Model 2: On Virtual Machines

• Physical Server → VM → Containerization Platform → Containers

• More popular due to:

  • Reduced maintenance overhead

  • Better cloud integration

  • No need to manage physical infrastructure

Docker: Popular Containerization Platform

Docker Lifecycle

1. Dockerfile creation

2. Image building (using docker build)

3. Container creation (using docker run)

Key Components:

• Docker Engine: Central component that manages containers

• Docker File: Instructions for building images

• Docker Image: Template for containers

• Docker Container: Running instance of an image

Modern Alternatives: Buildah

Why Buildah?

Docker has some limitations:

• Docker Engine as a single point of failure

• Layer management complexity

• Storage efficiency concerns

Buildah offers:

• No single point of failure

• Better integration with modern tools (Podman, Skopeo)

• Shell script-based approach instead of Dockerfiles

• OCI-compliant image creation

Security Considerations

• VMs provide stronger isolation due to complete OS separation

• Containers offer logical isolation but share host OS resources

• Container security requires additional considerations and policies

Best Practices

1. Use official base images

2. Keep containers lightweight

3. Follow security best practices

4. Understand the differences between VMs and containers

5. Choose the right deployment model for your needs

Conclusion

Containers represent a powerful evolution in virtualization technology, offering a balance between resource efficiency and application isolation. While they may not completely replace VMs in all scenarios, they provide significant advantages for modern application deployment and management.

---