K8S Concepts

Concepts study here:

https://kubernetes.io/docs/concepts/overview/what-is-kubernetes/

kubeadm init

1. Kubeadmin init pre-flight check

   Check the version of K8S/OS, user(root), host, port, tools etc.

2. Genrate key and certification

   /etc/kubernetes/pki

3. Generate kubeconfig file

   .kube/config /etc/kubernetes/*.conf KUBECONFIG

4. Generate manifest file

   /etc/kubernetes/manifests

5. Download the image, wait for starting

   Download from k8s.gcr.io

   kubeadmin waits for response from localhost:6443.healthz (liveessProde, config by manifests/kube-piserver.yaml)

6. Save master configuration information

7. Mark master sign on current node

8. Config TLS

9. Install DNS and kube-proxy

   deploy kube-proxy via daemonSet

   deploy kibe-dns

kubeadm join

add nodes to cluster

Disovery-token-ca-cert-hash: used by node to check master

token: used by master to check node

kubelet

Kubelet runs on all K8S nodes (including master), launched by OS init process(like systemd).

Node pod manager

config by /etc/systmd/system/kubelet.service.d/10 -kubeadm.conf

systemctl daemon-reload & systemctl estart kubelet

kube-apiserver

lauched by kubelet via static pod

Pod spec: /etc/kubernetes/manifests/kube-apiserver.yaml

Etcd

Lauched by kubelet via static pod

Communicate with api-server based on TLS

Runtime data saved in /var/lib/etcd

kube-controller-manager

Responsible for nodes/pod/namespace/service account/service endpoint/resource in cluster

/etc/kubernetes/manifests/kube-controller-manager.yaml

kube-scheduler

Scheduler for pod

Lauched by kubelet via static pod

kube-proxy

Config: /var/lib/kube-proxy/config.conf (pod)