caching strategies for high-traffic read workloads

hey everyone, i've been thinking a lot about caching lately, especially for services that see a ton of reads. we're trying to reduce database load and improve response times. what are your go-to caching strategies? are you primarily using in-memory caches like redis or memcached, or looking at more complex solutions like cdn caching or even application-level caching? how do you handle cache invalidation when data changes? any war stories or best practices you can share