- This is the primary management component in Kubernetes.
- When you run a
kubectl command, this is what talks to the `kube-api` server.
- The
kube-api server firstly authenticates the request and then validates it.
- It then retries the data from the
etcd cluster and then responds back with the requested information (showing the output of kubectl get nodes for example)
- Can also implement the APIs directly by sending a post request.
- The
kubeapi-server creates a pod object, without assigning it to a node.
- It then updates the information in the
etcd cluster.
- It then updates the user that the pod has been created.
- The Scheduler continuously monitors the
kubeapi-server
- The Scheduler identifies the right node to place the pod on.
- It indicates this back to the
kubeapi-server
- The
kubeapi-server then updates the information in the etcd cluster.
- The information is then passed to the Kubelet, in the appropriate worker node.
- The kubelet then creates the pod on the node and instructs the container runtime to deploy the application image.
- Once done, the kubelet updates the status back to the API server.
- The
kubeapi-server then updates the data back into the etcd cluster.
- A similar pattern is followed as soon as a change is requested. The
kubeapi-server is the heart of all of the tasks and changes in the cluster.
- The above is not required, if you bootstrapped using the
kubeadm tool.
- You can download and configure the
kube-api server to run on your Master Node.
- The
kube-api server is ran with a lot of parameters.
- Not need to understand all of the options right now.
- Having a high level understanding is good, when you configure the cluster from scratch.
- All components in a Kubernetes cluster need to know where they are.
- A lot of the components in the above config file are certificates, which are needed for the connectivity between different components.
- These are part of the SSL / TLS certificates.
- The option
etcd-servers is where you specify the location of the etcd server.
- This is how the
kube-api server connects to the etcd servers.
- How to view the
kube-api options in an existing cluster?
- An example is
kubectl get pods -n kube-system
- If you set up the cluster with the
kubeadm tool, the kubeadm tool deploys the kube-api server as a pod like so:
- You can see the
api-server options in the /etc/kubernetes/manifests/kube-apiserver.yaml file.
- In a non
kubeadm setup, you can inspect the options in the systemd kubeapi service file.
- You can also see the running process and the implemented options, by running
ps -aux | grep kube-apiserver. Run this on the Master Node.
