In this chapter, we tackled issues concerning running Prometheus at scale. Even though a single Prometheus instance can get you a long way, it's a good idea to have the knowledge to grow if required. We've learned how vertical and horizontal sharding works, when to use sharding, and what benefits and concerns sharding brings. We were introduced to common patterns when federating Prometheus (hierarchical or cross-service), and how to choose between them depending on our requirements. Since, sometimes, we want more than the out-of-the-box federation, we were introduced to the Thanos project and how it solves the global view problem.

In the next chapter, we'll be tackling another common requirement and one that isn't a core concern of the Prometheus project, which is the long-term storage of time series.