Caching is one of the most effective ways to achieve fast performance, probably the main one, but in a GraphQL context it’s not that easy: once we get to caching GraphQL queries in order to speed up our application backend, we also need to refresh the cache. How can we do that? What are the strategies we can apply to keep our dynamic data ready to use and up to date at the same time? How can we invalidate the cache efficiently? Time based invalidation is widely used but not very precise, so let's introduce event based invalidation, with node.js, fastify and mercurius!