Day 5: Load Balancers and CDNs | Networking for Developers

Load Balancers

A load balancer sits in front of your servers and distributes incoming requests across them. Without one, a single server handles everything — one failure takes down the site.

Load Balancing Algorithms

Round Robin: 1→2→3→1→2→3 (simple, even distribution)
Least Connections: route to the server with fewest active connections
IP Hash: same client always goes to same server (session affinity)
Weighted: server A gets 70% of traffic, server B gets 30%

Nginx as Load Balancer

upstream app_servers {
  least_conn;  # least connections algorithm
  server app1.example.com:3000;
  server app2.example.com:3000;
  server app3.example.com:3000;
}

server {
  listen 80;
  location / {
    proxy_pass http://app_servers;
    proxy_set_header Host $host;
    proxy_set_header X-Real-IP $remote_addr;
  }
}

CDNs

# CDN = Content Delivery Network
# Copies your static assets to edge servers worldwide
# User gets content from nearest edge, not your origin server

# Cloudflare: free tier, DNS + CDN + DDoS protection
# Add your domain → change nameservers to Cloudflare
# All traffic routes through Cloudflare edge

# Cloudflare handles:
# - Static asset caching
# - DDoS protection
# - TLS termination (HTTPS for free)
# - Firewall rules
# - Bot protection

ℹ️

Cloudflare's free tier is remarkably capable. For most sites: point your DNS to Cloudflare, enable the proxy (orange cloud), and you instantly get a CDN, HTTPS, and DDoS protection. Takes 5 minutes.

📝 Day 5 Exercise

Set Up Cloudflare

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Day 5 Summary

Load balancers distribute traffic across multiple servers for reliability and scale.
CDNs cache content at edge locations globally — users get the nearest copy.
Cloudflare free tier = CDN + HTTPS + DDoS protection + firewall. Use it for every site.
TLS termination at the load balancer/CDN means your origin servers don't need to handle HTTPS.

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