Kubernetes 06: The Kubelet

Follows Kubernetes 05: The Scheduler, which wrote down which node a pod belongs to; this lesson is the thing that reads that decision and makes it real.

Before you start. This series builds a small copy of Kubernetes: a program that keeps a fleet of machines running the programs you asked for, and restarts them when one dies. Kubernetes calls one running copy of a program a pod, the machine it runs on a node, and the whole fleet together the cluster. A program ships as an image, a sealed package of the program and everything it needs; a container is one running copy started from it, and a pod holds one or more containers. Our build can already do five things: hold a plain written description of what should be running, compare that description to reality and act on the gap forever, keep every description in one shared store that everyone reads and writes, split that watching job across many small watchers instead of one giant one, and decide which node a new pod should run on. This lesson is the one piece that turns that decision into a program actually running.