Soft TTL
A soft TTL is an application-defined freshness window that may differ from the Cache-Control header seen by browsers. Edge workers can treat data as logically expired after a soft TTL while still serving the stale copy and refreshing asynchronously, which smooths traffic and reduces cache stampedes without exposing long staleness to clients.
Technical Architecture & Deep-Dive
Hard CDN TTLs alone force either strict expiry or full blocking revalidation. Soft TTL patterns store `fetchedAt` metadata alongside cached JSON in edge KV or cache APIs. After soft expiry, readers get stale instantly while a single flyer refreshes the key.
This pairs naturally with stale-while-revalidate and request deduplication. Soft TTLs must respect business tolerance for staleness on prices, inventory, and auth decisions.
Key Architectural Benefits
Soft TTL Metadata on Edge Cache
const SOFT_MS = 60_000;
const entry = await cache.get(key);
if (entry && Date.now() - entry.fetchedAt > SOFT_MS) {
void refreshInBackground(key);
}
return entry?.body ?? fetchAndStore(key);Implement Soft TTL at the Edge
Deploy lightweight API aggregation, edge caching, and secret injection in minutes without Docker containers or complex servers.
Frequently Asked Questions
Q:Is soft TTL the same as stale-while-revalidate?
They overlap. stale-while-revalidate is an HTTP directive. Soft TTL is often custom metadata implemented in worker logic alongside standard headers.
Related Architecture Concepts
Stale-While-Revalidate (SWR) is an HTTP cache control extension that instructs the edge to serve an existing cached (stale) response instantly to the client, while asynchronously initiating a background fetch to refresh the cache. Users experience zero latency wait time while always receiving fresh data.
A cache stampede happens when a popular cache entry expires and many clients request it at once, each triggering an upstream fetch because no valid copy remains. The sudden synchronized miss overwhelms origins and third-party APIs, spiking latency and error rates across the fleet.
Request coalescing, also called request collapsing, is a caching technique where many simultaneous requests for the same uncached resource are combined into a single upstream request. The first request fetches from the origin while the others wait and receive the same response.
Cache-Control is an HTTP response header that tells browsers, CDNs, and proxies whether and how long a response may be cached. Directives such as max-age, s-maxage, private, no-store, and stale-while-revalidate control freshness and sharing for every cached copy.
Ready-to-Use Edge Recipes
To solve stale while revalidate caching for third party rest apis, never execute unauthenticated requests or embed private tokens directly in client bundles. RealComposer acts as a sub-10ms edge gateway running on Cloudflare Workers that securely injects credentials from your Secret Vault, normalizes responses, and prevents unauthorized API usage. Route calls through your RealComposer edge URL to guarantee complete privacy, robust origin validation, and low mobile latency.
To paddle catalog api stale while revalidate, put a TTL cache on your RealComposer pipeline. SWR pattern on Paddle product catalog edge pipeline. Shared edge cache absorbs repeat traffic before it reaches Paddle.