I have created a k8s cluster using kubeadm and have a couple of questions about the kube-controller-manager and kuber-apiserver components.
When created using kubeadm, those components are started as pods, not systemd daemons. If I kill any of those pods, they are restarted, but who is restarting them? I haven't seen any replicacontroller nor deployment in charge of doing that.
What is the "right" way of updating their configuration? Imagine I want to change the authorization-mode of the api server. In the master node we can find a /etc/kubernetes/manifests folder with a kube-apiserver.yaml file. Are we supposed to change this file and just kill the pod so that it restarts with the new config?
The feature you've described is called Static Pods. Here is a part of documentation that describes their behaviour.
Static pods are managed directly by kubelet daemon on a specific node, without the API server observing it. It does not have an associated replication controller, and kubelet daemon itself watches it and restarts it when it crashes. There is no health check. Static pods are always bound to one kubelet daemon and always run on the same node with it.
Kubelet automatically tries to create a mirror pod on the Kubernetes API server for each static pod. This means that the pods are visible on the API server but cannot be controlled from there.
The configuration files are just standard pod definitions in json or yaml format in a specific directory. Use kubelet
--pod-manifest-path=<the directory>to startkubeletdaemon, which periodically scans the directory and creates/deletes static pods as yaml/json files appear/disappear there. Note that kubelet will ignore files starting with dots when scanning the specified directory.When kubelet starts, it automatically starts all pods defined in directory specified in
--pod-manifest-path=or--manifest-url=arguments, i.e. our static-web.
Usually, those manifests are stored in the directory /etc/kubernetes/manifests.
If you put any changes to any of those manifests, that resource will be adjusted just like if you would run kubectl apply -f something.yaml command.