Kubernetes Master - Control Plane

Master Nod Bileşenleri Nedir?

Master Nod aynı zamanda Kubernetes Control Plane olarak ta adlandırılıyor. Açıklaması şöyle.

Kubernetes Control Plane

From a high level, a kubernetes architecture consists of a control plane (master), a distributed storage system for keeping the cluster state consistent (etcd), and a number of cluster nodes (Kubelets).

Master Node bileşenleri şöyle

The control plane is made up of five major components:

- Kube-apiserver

- Kube-controller-manager

- Kube-scheduler

- Etcd

- Cloud-controller-manager

Şeklen şöyle

Çoklu Master

Şekillerden de görülebildiği gibi Control Plane üzerinde birden fazla master olabilir. Açıklaması şöyle

Using multiple master nodes in your Kubernetes cluster lets you achieve high availability. If you have more masters, there is a lower likelihood of a failure that brings down your cluster.

Adding master nodes can also enhance performance because the critical Kubernetes components can leverage more hosting resources. For example, Kubernetes utilizes the shared resources of your masters to power the API server and scheduler. Thus, you can add one or several master nodes to boost your cluster’s performance.

Kube-apiserver Nedir?

Kubernetes API Server yazısına taşıdım.

Kube-scheduler 

Kubernetes Scheduler yazısına taşıdım.

Kube-controller-manager

Açıklaması şöyle. Worker'ları ve pod'ları izler. Eğer bir pod çökerse, kube-scheduler'ı kullanarak yeni pod yaratılmasını sağlar.

The Controller Manager is a daemon that runs the core control loops, watches the state of the cluster, and makes changes to drive status toward the desired state. The Cloud Controller Manager integrates into each public cloud for optimal support of availability zones, VM instances, storage services, and network services for DNS, routing and load balancing.

etcd Nedir? - Veri tabandır

Açıklaması şöyle. Cluster seviyesindeki tüm değişiklikleri kaydeder.

Consistent and highly-available key value store used as Kubernetes’ backing store for all cluster data.

If your Kubernetes cluster uses etcd as its backing store, make sure you have a back up plan for those data.

Açıklaması şöyle

Kubernetes uses etcd as it’s main backend database. It stores all configuration data in key-value format in etcd. If you lose etcd, your Kubernetes will stop working. Kubernetes uses etcd to store its actual state and desired state of the system. It then uses etcd watch functionality to monitor changes and based on that reconcile actual v/s desired state.

Açıklaması şöyle. Yani ekranda bilgi gösteren her şey etcd veri tabanından geliyor.

Basically, every info for a “kubectl get XXX" comes from the etcd server and is therefore rightly termed as the brain of any kubernetes cluster.

Cloud-controller-manager Nedir?

Açıklaması şöyle.

The cloud controller manager lets you link your cluster into your cloud provider’s API, and separates out the components that interact with that cloud platform from components that only interact with your cluster.

Note: If you are running Kubernetes on your own premises, or in a learning environment inside your own PC, the cluster does not have a cloud controller manager.

The following controllers can have cloud provider dependencies:

- Node controller: For checking the cloud provider to determine if a node has been deleted in the cloud after it stops responding

- Route controller: For setting up routes in the underlying cloud infrastructure

- Service controller: For creating, updating and deleting cloud provider load balancers