Kuberanetes: Robust management of multi-container applications

 The Kubernetes project - sometimes abbreviated as k8s- was born out of an internal container management project at Google known as Borg. Kubernetes comes from the Greek word for navigator, as denoted by the seven-spoke whell of the project's log. Kubernetes is written in the Go protgramming language and provids a robust framework to deploy and manage Docker container applications on the underlying resources managed by cloud proviers(such as Amazon Web Service(AWS), Microsoft Azure, and Google Cloud Platform(GCP)).

Kubernetes is fundamentally a tool to control applications composed of one or more Docker containers deployed in the cloud: this collection fo containers is known as a pod. Each pod can bave one or more copies (to allow redundancy), which is known as a replicaset. The two main components of a Kubernetes deployment are a control plane and nodes. The control plane hosts the centralized log for ldeploying and managing pods, and consists of (Figure 2.4):

- Kube-api-server: This is the main application that listens to commands from the user to deploy or update a pod, or manages external access to pods via ingress.

- Kube-controller-manager: An application to manage functions such as controlling the number of replicas per pod.

- Cloud-controller-manager: Manages functions particular to a cloud provider.

- Etcd: A key-value store that maintains the environment and state variables of different pods.

- Kube-scheduler: An application that is responsibile for finding workers to run a pod.

While we could set up own control plane, in practice we will usually have this function managed by our cloud provider, such as Google Kubernetes Engine(GKE) or Amazon's Elastic Kubernetes Services(EKS). The Kubernetes nodes-the individual machines in the cluster - each run an application known as a kubelet, which monitors the pod(s) running on that node.

Now that we have a high-level view of the Kubernetes system, let's look at the important commands you will need to interact with a Kubernetes cluster, update its components, and start and stop applications.