Docker Cluster Management

This chapter covers Docker cluster management technologies, including Docker Swarm and Kubernetes basics.

Why Cluster Management?

Single-host Docker faces production challenges:

Problem	Description
Single point of failure	One server down, all services unavailable
Resource bottleneck	Limited single-machine resources
Load balancing	No automatic traffic distribution
Service discovery	Difficult cross-node communication

Docker Swarm

Docker Swarm is Docker's built-in cluster management and orchestration tool.

Architecture

┌─────────────────────────────────────────────┐
│              Docker Swarm Cluster            │
│                                             │
│  ┌──────────┐  ┌──────────┐  ┌──────────┐  │
│  │ Manager  │  │ Manager  │  │ Manager  │  │
│  │  Node 1  │  │  Node 2  │  │  Node 3  │  │
│  └────┬─────┘  └────┬─────┘  └────┬─────┘  │
│       │              │              │        │
│  ┌────▼─────┐  ┌────▼─────┐  ┌────▼─────┐  │
│  │ Worker   │  │ Worker   │  │ Worker   │  │
│  │  Node 1  │  │  Node 2  │  │  Node 3  │  │
│  └──────────┘  └──────────┘  └──────────┘  │
└─────────────────────────────────────────────┘

Initialize Swarm

docker swarm init --advertise-addr <MANAGER-IP>
# Run the output join command on Worker nodes
docker node ls

Deploy Services

docker service create --name web --replicas 3 -p 80:80 nginx:latest
docker service ls
docker service ps web
docker service scale web=5
docker service update --image nginx:1.25 web
docker service rm web

Deploy with Stack

# docker-stack.yml
version: '3.8'
services:
  web:
    image: nginx:latest
    deploy:
      replicas: 3
      update_config:
        parallelism: 1
        delay: 10s
      restart_policy:
        condition: on-failure
    ports:
      - "80:80"

docker stack deploy -c docker-stack.yml myapp
docker stack ls
docker stack services myapp
docker stack rm myapp

Kubernetes Introduction

Kubernetes (K8s) is the most popular container orchestration platform.

Core Concepts

Concept	Description
Pod	Smallest deployment unit, contains one or more containers
Deployment	Manages Pod replicas and updates
Service	Provides stable network access to Pods
Namespace	Logical resource isolation
ConfigMap	Configuration management
Secret	Sensitive information management

Try K8s with Docker Desktop

1. Open Docker Desktop → Settings → Kubernetes
2. Check "Enable Kubernetes"
3. Click "Apply & Restart"

kubectl cluster-info
kubectl get nodes

Basic Operations

kubectl create deployment web --image=nginx --replicas=3
kubectl expose deployment web --port=80 --type=NodePort
kubectl get pods
kubectl get services
kubectl scale deployment web --replicas=5
kubectl set image deployment/web nginx=nginx:1.25
kubectl logs <pod-name>
kubectl delete deployment web

Docker Swarm vs Kubernetes

Feature	Docker Swarm	Kubernetes
Learning curve	Low	High
Setup complexity	Simple	Complex
Feature richness	Basic	Very rich
Community ecosystem	Smaller	Very large
Scale	Small-medium	Large
Docker integration	Native	Requires extra config
Auto-scaling	Manual	Supported

Choosing

• Docker Swarm: Small-medium teams, quick setup, simple cluster needs
• Kubernetes: Large teams, complex microservices, rich ecosystem support needed

Chapter Summary

Cluster management is key to running containerized applications in production. Docker Swarm offers simplicity, while Kubernetes is the industry standard for large-scale orchestration. Choose based on team size and business requirements.

Further Reading

• Docker Swarm Documentation
• Kubernetes Official Documentation