Sometimes Node.js needs to do some heavy lifting, performing CPU or network intensive tasks and yet respond quickly on incoming requests. For repetitive tasks like Server side rendering of markup or parsing big JSON responses caching can give the application a great performance boost. Since many requests may hit the server concurrently, you do not want more than one worker to run for a given resource at the same time. In addition - serving stale content when a backend resource is down may save your day! The intention of nodecache-as-promised is to give you a fairly simple interface, yet powerful application cache, with fine-grained control over caching behaviour. nodecache-as-promised is inspired by how Varnish works. It is not intended to replace Varnish (but works great in combination). Whereas Varnish is a high-performant edge/burst/failover cache, working as a reverse proxy and loadbalancer, it depends on a fast backend when configured with short a cache window (ie. TTL ~1s). It uses URLs in combination with cookies as keys for its cached content. Since there are no restrictions on conformant URLs/cookies for clients requesting content, it is quite easy to bust it's cache without any security measures. nodecache-as-promised on the other hand is running at application level for more strict handling of cache keys, and may use many different caches and policies on how the web page is built.