Entrega de Imagens por CDN em Menos de 50ms

User in Tokyo requests: https://cdn.example.com/images/hero.jpg

1. DNS Resolution (anycast)
   -> DNS returns IP 198.51.100.1
   -> Anycast routes to nearest PoP: Tokyo edge server

2. Edge Server (Tokyo PoP)
   Cache HIT?  -> Serve from memory/SSD (1-5ms processing)
                  Total latency: ~10-20ms (nearby network hop)

   Cache MISS? -> Check regional mid-tier cache

3. Mid-Tier Cache (Asia-Pacific region, e.g. Singapore)
   Cache HIT?  -> Return to Tokyo edge, cache locally, serve user
                  Added latency: ~30-60ms for regional hop

   Cache MISS? -> Fetch from origin

4. Origin Server (US-East)
   -> Serves the image
   -> Mid-tier caches it (TTL: 24 hours)
   -> Edge caches it (TTL: 1 hour)
   -> User gets the image
   Total first-request latency: ~200-300ms
   All subsequent Tokyo requests: ~10-20ms

# Simplified CDN edge server config
proxy_cache_path /var/cache/cdn levels=1:2
    keys_zone=images:100m
    max_size=50g
    inactive=24h
    use_temp_path=off;

server {
    listen 443 ssl http2;
    server_name cdn.example.com;

    location /images/ {
        proxy_cache images;
        proxy_cache_valid 200 1h;
        proxy_cache_valid 404 1m;

        # Serve stale content while revalidating in background
        proxy_cache_use_stale updating error timeout;
        proxy_cache_background_update on;

        # Add cache status header for debugging
        add_header X-Cache-Status $upstream_cache_status;
        add_header Cache-Control "public, max-age=3600";

        # Conditional requests to origin
        proxy_cache_revalidate on;

        proxy_pass http://origin-servers;
    }
}

# Check if an image is served from cache
curl -sI https://cdn.example.com/images/hero.jpg | grep -E '(X-Cache|Age|Cache-Control|CF-Cache)'

# Example output:
# X-Cache: HIT
# Age: 3542           <- seconds since edge cached it
# Cache-Control: public, max-age=3600
# CF-Cache-Status: HIT   <- Cloudflare-specific header

# Purge a specific cached image (Cloudflare API example)
curl -X POST "https://api.cloudflare.com/client/v4/zones/{zone_id}/purge_cache" \
  -H "Authorization: Bearer $CF_TOKEN" \
  -H "Content-Type: application/json" \
  --data '{"files":["https://cdn.example.com/images/hero.jpg"]}'