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Discussion on: What exactly is Kubernetes anyway?

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Tim Downey • Edited on

Good post!

One minor thing I want to point out is that there is no single component called the controller (though there is a kube-controller-manager component). Rather, controller in Kubernetes is more of a generic term for processes that implement state reconciliation / control-loops. For example, there's an Endpoints Controller that continuously watches Services and Pods to update the relevant Endpoint resources. And there's a ReplicaSet Controller that makes sure the number of running Pods desired by ReplicaSet is correct.

There's a whole bunch of them and the standard ones run as part of the kube-controller-manager, but additional stuff you may install on your cluster often comes with its own controllers.

As you mentioned, these things run continuously to make sure the actual state of the cluster matches your desired state of things.

Just wanted to point this out cause as you get deeper into Kubernetes you'll see folks talk about controllers all the time and they're not necessarily talking about the built-in ones.

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Sarah πŸ¦„ Author

Thank you so much for this explanation, it’s really helpful!!