CDN — Serve Content From the Edge

Distribute static and cacheable content from edge nodes near users — offload your origin and reduce latency globally.

When to use

• Static assets (images, JS, CSS) and public API responses with low mutation rate
• Global user base with latency-sensitive delivery

Tradeoffs

• Cache invalidation at edge nodes is eventual — purge propagation takes time
• Personalized or auth-gated content needs careful Cache-Control or bypass rules

Go

// Cache-Control headers for CDN edge caching
func ServeAsset(w http.ResponseWriter, r *http.Request) {
    // Versioned asset: immutable, cache forever
    if isVersioned(r.URL.Path) {
        w.Header().Set("Cache-Control", "public, max-age=31536000, immutable")
    } else {
        // Serve stale while revalidating in background
        w.Header().Set("Cache-Control", "public, max-age=60, stale-while-revalidate=60")
    }
    http.ServeFile(w, r, assetPath(r.URL.Path))
}

func PurgeEdgeCache(path string) error {
    _, err := cdnClient.Purge(ctx, &cdn.PurgeRequest{Paths: []string{path}})
    return err
}

Python

from flask import Flask, send_file, request

app = Flask(__name__)

@app.route("/assets/<path:filename>")
def serve_asset(filename):
    resp = send_file(f"static/{filename}")
    if is_versioned(filename):
        resp.headers["Cache-Control"] = "public, max-age=31536000, immutable"
    else:
        resp.headers["Cache-Control"] = "public, max-age=60, stale-while-revalidate=60"
    return resp

def purge_edge_cache(path: str):
    cdn_client.purge(paths=[path])

Gotcha: Set Cache-Control: stale-while-revalidate=60 for content that can be briefly stale. It serves cached content immediately while revalidating in the background — zero latency spike on expiry.