Docker and Kubernetes: Getting Started

Docker and Kubernetes are the two most important technologies in modern server infrastructure. Docker provides lightweight containerization, while Kubernetes (K8s) orchestrates containers at scale. Together, they form the foundation of cloud-native application deployment.

What Are Containers?

Containers are lightweight, isolated environments that package an application with all its dependencies. Unlike virtual machines, containers share the host OS kernel, making them:

Faster to start — seconds vs minutes for VMs
More resource-efficient — no separate OS per instance
Portable — runs identically on any system with Docker installed
Reproducible — same environment in development, testing, and production

Docker Basics

Installing Docker

On Ubuntu/Debian:

curl -fsSL https://get.docker.com sh sudo usermod -aG docker $USER

Key Concepts

Image — a read-only template containing the application and dependencies
Container — a running instance of an image
Dockerfile — instructions for building an image
Docker Hub — public registry for sharing images

Essential Docker Commands

docker pull nginx # download an image docker run -d -p 80:80 nginx # run container in background docker ps # list running containers docker logs container_name # view container logs docker exec -it container_name bash # open shell in container docker stop container_name # stop container docker rm container_name # remove container

Dockerfile Example

FROM python:3.11-slim WORKDIR /app COPY requirements.txt . RUN pip install -r requirements.txt COPY . . EXPOSE 8000 CMD ["python", "app.py"]

Build and run:

docker build -t myapp . docker run -d -p 8000:8000 myapp

Docker Compose

For multi-container applications, use Docker Compose:

version: '3.8' services: web: build: . ports: - "80:80" db: image: postgres:15 environment: POSTGRES_PASSWORD: secret volumes: - pgdata:/var/lib/postgresql/data volumes: pgdata:

Run with: docker compose up -d

Kubernetes Introduction

Kubernetes (K8s) manages containers across multiple servers. It handles:

Scheduling — decides which node runs each container
Scaling — automatically adjusts the number of container replicas
Self-healing — restarts failed containers, replaces unresponsive nodes
Load balancing — distributes traffic across container instances
Rolling updates — deploys new versions with zero downtime

Key Kubernetes Concepts

Pod — smallest deployable unit, contains one or more containers
Service — stable network endpoint for a set of pods
Deployment — manages pod replicas and updates
Namespace — logical isolation within a cluster
Ingress — HTTP routing and load balancing

When to Use Kubernetes

Kubernetes adds complexity. It is worth using when:

You run 10+ microservices
You need automatic scaling
High availability is critical
You have a team to manage the infrastructure

For simpler setups, Docker Compose on a single VPS or dedicated server is often sufficient.