What is apiserver?

Kubernetes apiserver is a library that lets developers build their own API servers that behave like the ones powering Kubernetes. In practical terms, if you want to create a system where users can manage resources through the same kubectl command-line tool they already use for Kubernetes, with built-in authentication, authorization, and discovery, this library gives you the foundational pieces to do that. At a high level, Kubernetes has an API that lets you define things like "I want three instances of this application running" and the system handles it. An "aggregated API server" extends that idea: it lets you plug in additional APIs that feel native to Kubernetes, as if they were part of the core system. This library provides the plumbing for that, handling things like verifying who a user is, checking whether they're allowed to do what they're asking, exposing what API endpoints exist so tools can discover them automatically, and supporting multiple versions of those APIs. The primary users are developers building Kubernetes extensions or Kubernetes-like platforms. For example, if you're building a service catalog (a way to offer consumable services within a Kubernetes environment) or creating a custom resource type that needs its own API logic, you'd use this library to get a server that speaks Kubernetes' language without reinventing all the surrounding infrastructure. The README mentions its first consumers include Kubernetes itself, the kube-aggregator project, and a service catalog project. One important caveat: this library currently makes no compatibility guarantees. It tracks Kubernetes closely and changes frequently, meaning if you build on it, your code may need updating when Kubernetes updates. The project's goal is to eventually make this cleaner and more stable, but right now it's tightly coupled to Kubernetes' own development pace. Additionally, the repository is read-only, you can't contribute directly here. All changes happen in the main Kubernetes repository and get synced over automatically.