container.training/slides/k8s/declarative.md

Declarative vs imperative in Kubernetes

• With Kubernetes, we cannot say: "run this container"

• All we can do is write a spec and push it to the API server

  (by creating a resource like e.g. a Pod or a Deployment)

• The API server will validate that spec (and reject it if it's invalid)

• Then it will store it in etcd

• A controller will "notice" that spec and act upon it

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Reconciling state

• Watch for the spec fields in the YAML files later!

• The spec describes how we want the thing to be

• Kubernetes will reconcile the current state with the spec
  (technically, this is done by a number of controllers)

• When we want to change some resource, we update the spec

• Kubernetes will then converge that resource