Containerization: The Ultimate Cheat Sheet

Introduction: What Is Containerization and Why It Matters

Containerization is a lightweight virtualization technology that packages applications and their dependencies into standalone, portable units called containers. Unlike traditional virtual machines, containers share the host system’s OS kernel while maintaining isolation. This approach enables consistent deployment across different environments, from development to production.

Containerization matters because it:

• Ensures consistent application behavior across environments
• Improves resource efficiency compared to VMs
• Accelerates development and deployment cycles
• Simplifies scaling and orchestration
• Enhances security through isolation

Core Concepts and Principles

Container Lifecycle Management

1. Build an image from a Dockerfile or base image
2. Push the image to a container registry
3. Pull the image to the target environment
4. Run a container from the image
5. Manage the container: start, stop, restart, pause
6. Delete the container when no longer needed

Key Tools and Technologies

Container Engines and Runtimes

• Docker: The most popular containerization platform
• containerd: A container runtime used by Docker and Kubernetes
• CRI-O: Lightweight container runtime for Kubernetes
• Podman: Daemonless container engine (Red Hat alternative to Docker)
• LXC/LXD: Linux container hypervisor

Container Orchestration

• Kubernetes: The leading container orchestration platform
• Docker Swarm: Docker’s native orchestration solution
• Amazon ECS/EKS: AWS container services
• Azure AKS: Microsoft’s managed Kubernetes service
• Google GKE: Google’s managed Kubernetes service

Container Registries

• Docker Hub: Public repository for Docker images
• Amazon ECR: AWS container registry
• Google Container Registry: Google Cloud’s registry
• Azure Container Registry: Microsoft’s container registry
• GitHub Container Registry: GitHub’s container registry service
• Harbor: Open-source container registry with security features

Docker Commands Cheat Sheet

Basic Commands

# Pull an image
docker pull <image>:<tag>

# Run a container
docker run [options] <image>:<tag>

# List running containers
docker ps

# List all containers (including stopped)
docker ps -a

# Stop a container
docker stop <container_id>

# Remove a container
docker rm <container_id>

# List images
docker images

# Remove an image
docker rmi <image_id>

# Build an image from Dockerfile
docker build -t <name>:<tag> <path>

# Execute command in running container
docker exec -it <container_id> <command>

Container Management

# Run container in background
docker run -d <image>

# Run with port mapping
docker run -p <host_port>:<container_port> <image>

# Run with volume mounting
docker run -v <host_path>:<container_path> <image>

# Run with environment variables
docker run -e VAR_NAME=value <image>

# View container logs
docker logs <container_id>

# View container stats
docker stats <container_id>

Image Management

# Tag an image
docker tag <image_id> <repository>:<tag>

# Push to registry
docker push <repository>:<tag>

# Save image to tar file
docker save -o <file.tar> <image>

# Load image from tar file
docker load -i <file.tar>

# Inspect image
docker inspect <image_id>

Dockerfile Reference

# Base image
FROM <image>:<tag>

# Set working directory
WORKDIR /path/to/workdir

# Copy files from host to image
COPY <src> <dest>

# Download files during build
ADD <src> <dest>

# Run commands during build
RUN <command>

# Set environment variables
ENV KEY=value

# Define volume mount points
VOLUME /path/in/container

# Expose ports
EXPOSE <port>

# Default command to run
CMD ["executable", "param1", "param2"]

# Command that cannot be overridden
ENTRYPOINT ["executable", "param1"]

# Set metadata
LABEL maintainer="name@example.com"

Kubernetes Quick Reference

Basic kubectl Commands

# Create resources from YAML file
kubectl apply -f <file.yaml>

# Get resources
kubectl get <resource_type>

# Describe resource details
kubectl describe <resource_type> <resource_name>

# Delete resources
kubectl delete <resource_type> <resource_name>

# View logs
kubectl logs <pod_name>

# Execute command in pod
kubectl exec -it <pod_name> -- <command>

# Port forwarding
kubectl port-forward <pod_name> <local_port>:<pod_port>

Common Kubernetes Resources

• Pod: Basic execution unit containing one or more containers
• Deployment: Manages Pod replicas and updates
• Service: Exposes Pods as a network service
• ConfigMap: External configuration
• Secret: Sensitive configuration data
• PersistentVolume: Storage abstraction
• Namespace: Virtual cluster for resource isolation
• ReplicaSet: Ensures a specified number of Pod replicas
• StatefulSet: For stateful applications
• DaemonSet: Ensures a Pod runs on each node
• Ingress: External access to services

Comparison: Containers vs. Virtual Machines

Common Containerization Challenges and Solutions

Best Practices

Container Image Management

• Use specific version tags instead of latest
• Implement multi-stage builds to reduce image size
• Avoid storing secrets in images
• Minimize layers through command chaining
• Scan images for vulnerabilities

Security

• Run containers with non-root users
• Apply the principle of least privilege
• Keep base images updated
• Use read-only file systems where possible
• Implement network policies
• Scan images for vulnerabilities regularly

Performance

• Set appropriate resource limits
• Use lightweight base images
• Monitor container performance
• Implement proper health checks
• Optimize application for containerization

Operations

• Implement proper logging and monitoring
• Use infrastructure as code
• Automate deployment with CI/CD
• Implement backup and disaster recovery
• Practice blue/green deployments

Container Networking Models

Resources for Further Learning

Documentation

• Docker Documentation
• Kubernetes Documentation
• Podman Documentation
• containerd Documentation

Books

• “Docker Deep Dive” by Nigel Poulton
• “Kubernetes: Up and Running” by Brendan Burns, Joe Beda, and Kelsey Hightower
• “Cloud Native DevOps with Kubernetes” by John Arundel and Justin Domingus

Online Courses

• Kubernetes Certified Administrator (CKA) courses
• Docker Certified Associate (DCA) courses
• Cloud Native Computing Foundation (CNCF) training

Communities

• CNCF Slack channels
• Docker Community Forums
• Kubernetes Community Forums
• StackOverflow (docker and kubernetes tags)

Tools

• Kompose: Convert Docker Compose to Kubernetes
• Helm: Kubernetes package manager
• Lens: Kubernetes IDE
• Portainer: Container management UI
• Trivy: Container vulnerability scanner