Design a Content Delivery Network (CDN)

# Fastly VCL (Varnish Configuration Language) — Custom logic
# This is their core configuration language

sub vcl_recv {
  # Enable QUIC if client supports it
  if (req.http Upgrade ~ "quic") {
    set req.http.X-Proto = "HTTP/3";
  }

  # Route API requests to different backends
  if (req.url ~ "^/api/") {
    set req.backend = api_origin;
    # Don't cache API by default
    return(pass);
  }

  # Add surrogate key for targeted invalidation
  if (req.url ~ "^/products/") {
    set req.http.Surrogate-Key = "product/" req.url.path;
  }
}

sub vcl_fetch {
  # Override TTL based on response headers
  if (resp.http.Cache-Control ~ "max-age") {
    set beresp.ttl = std.duration(resp.http.Cache-Control.max-age, 3600s);
  }

  # Grace mode — serve stale if origin is unhealthy
  set beresp.grace = 24h;

  # Surrogate key from origin response header
  if (resp.http.Surrogate-Key) {
    set beresp.http.X-Surrogate-Key = resp.http.Surrogate-Key;
  }
}

sub vcl_deliver {
  # Add cache status header for debugging
  if (obj.hits > 0) {
    set resp.http.X-Cache = "HIT";
    set resp.http.X-Cache-Hits = obj.hits;
  } else {
    set resp.http.X-Cache = "MISS";
  }
}
        

# Akamai Property Manager (JSON-based configuration)
# Structured via Property Manager CLI or API

{
  "propertyRules": [
    {
      "name": "Static Asset Caching",
      "criteria": { "match": ["url", "/static/*"] },
      "behavior": {
        "caching": {
          "behavior": "cache-control",
          "max-age": 604800,
          "sharedMaxAge": 86400
        },
        "cpCode": 123456,
        "originShieldRegion": "US-EAST-2"
      }
    },
    {
      "name": "API Bypass",
      "criteria": { "match": ["url", "/api/*"] },
      "behavior": {
        "caching": { "behavior": "no-store" }
      }
    },
    {
      "name": "Image Optimization",
      "criteria": { "match": ["url", "*.jpg", "*.png"] },
      "behavior": {
        "imageOptimization": { "enable": true },
        "webp": { "enabled": true }
      }
    },
    {
      "name": "Origin Failover",
      "criteria": {},
      "behavior": {
        "failover": {
          "originTimeout": 5000,
          "maxRetries": 3,
          "retryOnTimeout": true
        }
      }
    }
  ]
}

# Akamai Purge API
# Purge by CP code or URL
POST /ccu/v3/invalidate/content
{
  "type": "cpcode",
  "objects": ["123456"],
  "domain": "production"
}