Nginx "stale while invalidate" caching

Using a cache to store dynamic content for short periods of time (ten minutes, an hour, etc.) to reduce load on an application server.

Allow serving old data (ex. from the last ten minutes) to all but the first requestor while attempting to acquire the latest data.

NGINX directives

proxy_cache_lock: allow only so many active requests to refill the cache

proxy_cache_use_stale: allow serving expired bread while a repopulation attempt is in flight