CDN cache hit ratio above 80% for static assets

A CDN cache hit ratio below 80% means most static asset requests are reaching your origin server rather than being served from an edge node. Each origin-served request adds 50–400ms of latency depending on user geography, and it multiplies your origin load. ISO 25010:2011 time-behaviour captures the latency cost; the operational consequence is higher infrastructure cost and slower asset delivery specifically for users furthest from your origin region.

Audit your CDN analytics dashboard (Vercel Analytics, Cloudflare, CloudFront) and look for assets with high miss rates. The most common cause is incorrect Cache-Control headers — check that hashed assets carry immutable, max-age=31536000.

// vercel.json — ensure immutable headers reach the CDN edge
{
  "headers": [
    {
      "source": "/_next/static/(.*)",
      "headers": [{ "key": "Cache-Control", "value": "public, max-age=31536000, immutable" }]
    }
  ]
}

• ID: performance-deep-dive.caching-cdn.cdn-cache-hit-ratio

• Severity: medium

• What to look for: Enumerate the CDN or edge caching configuration. Access CDN analytics dashboard (Vercel, Cloudflare, AWS CloudFront, etc.). Look for cache hit ratio metrics. A healthy hit ratio is above 80%.

• Pass criteria: CDN cache hit ratio for static assets is above 80%. Most requests are served from edge cache, not origin.

• Fail criteria: Cache hit ratio is below 80%, or CDN analytics are not available/not configured.

• Skip (N/A) when: The project does not use a CDN, or is too new to have meaningful cache statistics (requires 7+ days of traffic).

• Cross-reference: For cache header configuration that affects hit ratio, see cache-control-hashed-assets.

• Detail on fail: "CDN cache hit ratio is 32% — most requests hitting origin server instead of cache edges" or "No CDN configured; all requests served from single origin region"

• Remediation: Configure proper cache headers (see "Cache-Control headers optimized" check above). Ensure cache-busting works correctly so only changed assets are re-fetched.

  // vercel.json — ensure proper headers for CDN caching
  { "headers": [{ "source": "/static/(.*)", "headers": [{ "key": "Cache-Control", "value": "public, max-age=31536000, immutable" }] }] }