Containers vs Virtual Machines: Architecture Deep Dive

#!/bin/bash
# Containers vs VMs: Practical Demonstrations
# This script shows real commands to compare containers and VMs
echo "====================================================================="
echo "CONTAINERS vs VIRTUAL MACHINES: PRACTICAL COMPARISON"
echo "====================================================================="
echo ""
# ===========================
# PART 1: SIZE COMPARISON
# ===========================
echo "1. SIZE COMPARISON"
echo "---------------------------------------------------------------------"
echo ""
echo "Virtual Machine (typical sizes):"
echo "  - Ubuntu Server VM:     ~5-8 GB (full OS)"
echo "  - Windows Server VM:    ~15-20 GB (full OS)"
echo "  - With applications:    Add 1-5 GB per app"
echo "  - Total for 3 VMs:      ~30-50 GB"
echo ""
echo "Docker Containers (actual sizes from Docker Hub):"
echo "  - Alpine Linux:         5 MB (minimal base)"
echo "  - Ubuntu:              77 MB (full Ubuntu userland)"
echo "  - Python 3.11:         130 MB (Python runtime)"
echo "  - Node.js 18:          110 MB (Node.js runtime)"
echo "  - PostgreSQL:          380 MB (database)"
echo "  - Total for 3 apps:    ~500 MB - 1 GB"
echo ""
echo "💡 Containers are 30-50x smaller than equivalent VMs!"
echo ""
# ===========================
# PART 2: STARTUP TIME
# ===========================
echo "2. STARTUP TIME COMPARISON"
echo "---------------------------------------------------------------------"
echo ""
echo "Let's measure actual container startup time:"
echo ""
# Check if Docker is installed
if ! command -v docker &> /dev/null; then
    echo "⚠️  Docker not installed. Install Docker to run this demo."
    echo "   Visit: https://docs.docker.com/get-docker/"
    echo ""
else
    echo "Starting a lightweight container and measuring time..."
    echo ""
    
    # Pull Alpine image (if not present)
    docker pull alpine:latest &> /dev/null
    
    # Measure container startup time
    echo "$ time docker run alpine echo 'Container started!'"
    
    # Run and time it
    start_time=$(date +%s%N)
    docker run --rm alpine echo 'Container started!'
    end_time=$(date +%s%N)
    
    # Calculate milliseconds
    duration=$(( (end_time - start_time) / 1000000 ))
    
    echo ""
    echo "⏱️  Container startup time: ${duration}ms"
    echo ""
    echo "Compare to VM:"
    echo "  - Typical VM boot: 30,000-120,000ms (30-120 seconds)"
    echo "  - Container advantage: ~100x faster startup"
    echo ""
fi
# ===========================
# PART 3: RESOURCE USAGE
# ===========================
echo "3. RESOURCE USAGE (MEMORY & CPU)"
echo "---------------------------------------------------------------------"
echo ""
if command -v docker &> /dev/null; then
    echo "Running 3 containers to show resource efficiency..."
    echo ""
    
    # Start 3 lightweight containers in background
    docker run -d --name demo-container-1 --rm alpine sleep 3600 &> /dev/null
    docker run -d --name demo-container-2 --rm alpine sleep 3600 &> /dev/null
    docker run -d --name demo-container-3 --rm alpine sleep 3600 &> /dev/null
    
    # Give them a moment to start
    sleep 2
    
    echo "Container Resource Usage:"
    echo ""
    docker stats --no-stream --format "table {{.Name}}	{{.CPUPerc}}	{{.MemUsage}}"         demo-container-1 demo-container-2 demo-container-3
    
    echo ""
    echo "📊 Analysis:"
    echo "  - Each Alpine container uses ~1-2 MB of RAM"
    echo "  - 3 containers total: ~5-10 MB"
    echo "  - 3 equivalent VMs would use: ~15-20 GB"
    echo "  - Resource efficiency: ~2000x better"
    echo ""
    
    # Cleanup
    echo "Cleaning up demo containers..."
    docker stop demo-container-1 demo-container-2 demo-container-3 &> /dev/null
    echo "✅ Cleanup complete"
    echo ""
fi
# ===========================
# PART 4: ISOLATION DEMO
# ===========================
echo "4. ISOLATION DEMONSTRATION"
echo "---------------------------------------------------------------------"
echo ""
if command -v docker &> /dev/null; then
    echo "Showing process isolation with namespaces..."
    echo ""
    
    # Start a container in background
    docker run -d --name isolation-demo --rm alpine sleep 3600 &> /dev/null
    
    echo "HOST SYSTEM processes (PID namespace):"
    echo "  - Can see all system processes (thousands)"
    ps aux | wc -l | xargs echo "  - Total processes visible:"
    echo ""
    
    echo "CONTAINER processes (isolated PID namespace):"
    docker exec isolation-demo ps aux
    echo ""
    echo "📌 Notice: The container only sees 2 processes:"
    echo "   PID 1: sleep 3600 (main process)"
    echo "   PID 7: ps aux (our inspection command)"
    echo ""
    echo "This is namespace isolation in action!"
    echo ""
    
    # Cleanup
    docker stop isolation-demo &> /dev/null
fi
# ===========================
# PART 5: KERNEL SHARING DEMO
# ===========================
echo "5. KERNEL SHARING DEMONSTRATION"
echo "---------------------------------------------------------------------"
echo ""
echo "HOST SYSTEM kernel version:"
uname -r
echo ""
if command -v docker &> /dev/null; then
    echo "CONTAINER kernel version (same as host!):"
    docker run --rm alpine uname -r
    echo ""
    echo "💡 Key Insight: Container shares the host kernel!"
    echo "   - VMs would each have their own kernel"
    echo "   - Containers all use the same Linux kernel"
    echo "   - This is why containers are lightweight"
    echo ""
fi
# ===========================
# PART 6: USE CASE DECISION TREE
# ===========================
echo "6. DECISION GUIDE: WHEN TO USE WHAT"
echo "---------------------------------------------------------------------"
echo ""
echo "Use CONTAINERS when:"
echo "  ✅ Running microservices (many small services)"
echo "  ✅ Need rapid scaling (add/remove instances quickly)"
echo "  ✅ Consistent dev environments (same image everywhere)"
echo "  ✅ CI/CD pipelines (fast, reproducible builds)"
echo "  ✅ Cloud-native applications (Kubernetes, serverless)"
echo ""
echo "Use VIRTUAL MACHINES when:"
echo "  ✅ Need different operating systems (Linux + Windows)"
echo "  ✅ Maximum security isolation (different tenants)"
echo "  ✅ Legacy applications (specific kernel versions)"
echo "  ✅ Compliance requirements (strict isolation needed)"
echo "  ✅ Running untrusted code (stronger boundaries)"
echo ""
echo "Use BOTH (Hybrid) when:"
echo "  ✅ Modern apps in containers, legacy in VMs"
echo "  ✅ Different OS + microservices architecture"
echo "  ✅ Security zones (VMs) + scalable services (containers)"
echo ""
# ===========================
# SUMMARY
# ===========================
echo "====================================================================="
echo "SUMMARY: CONTAINERS vs VIRTUAL MACHINES"
echo "====================================================================="
echo ""
cat << 'EOF'
┌─────────────────┬──────────────────────┬──────────────────────┐
│ Characteristic  │ Virtual Machines     │ Containers           │
├─────────────────┼──────────────────────┼──────────────────────┤
│ Isolation       │ Hardware-level       │ Process-level        │
│ OS Required     │ Full OS per VM       │ Shared host kernel   │
│ Size            │ GBs (5-20 GB)        │ MBs (5-500 MB)       │
│ Startup Time    │ Minutes (30-120s)    │ Seconds (1-3s)       │
│ Performance     │ Near-native          │ Native               │
│ Density         │ 5-10 per server      │ 50-100+ per server   │
│ Portability     │ Moderate             │ Excellent            │
│ Use Case        │ Different OS, max    │ Microservices,       │
│                 │ isolation            │ cloud-native apps    │
└─────────────────┴──────────────────────┴──────────────────────┘
KEY TAKEAWAYS:
1. VMs virtualize hardware; containers virtualize the OS
2. Containers are 30-50x smaller and start 40-100x faster
3. VMs provide stronger isolation; containers are more efficient
4. Choose based on your needs-or use both together!
EOF
echo ""
echo "🎓 Next Steps:"
echo "   - Learn Docker architecture and how images work"
echo "   - Practice building your first container"
echo "   - Explore Docker networking and volumes"
echo ""
echo "====================================================================="