Etsy is a popular online e-commerce website. Because of this, they need to handle a lot of traffic. To handle all this traffic, an important caching layer is crucial. To understand the scale, this is a quote from the article.
Today, our caching clusters store terabytes of cached data and handle millions of lookups per second
In the article, they explain their caching architecture, what hashing algorithm do they use (and why) and how do they solve the problem of hot keys that would overload a single server.