serveWhileStale property

Serve existing content from the cache (if available) when revalidating content with the origin, or when an error is encountered when refreshing the cache.

This setting defines the default "max-stale" duration for any cached responses that do not specify a max-stale directive. Stale responses that exceed the TTL configured here will not be served. The default limit (max-stale) is 86400s (1 day), which will allow stale content to be served up to this limit beyond the max-age (or s-max-age) of a cached response. The maximum allowed value is 604800 (1 week). Set this to zero (0) to disable serve-while-stale.