What is Kubernetes Cluster?
Kubernetes is currently the most popular container orchestration platform. Being a robust and dynamic platform, it comes with a steep learning curve and has a lot of terms that are complex to understand especially for beginners.
One of those terms is the “Kubernetes cluster”, which is used often when talking about Kubernetes. This blog will help you get all the essential details of the Kubernetes cluster along with the information regarding its functioning, setup, and management. So, without further ado, let’s begin.
What Exactly is Kubernetes and Why is it Popular?
Being an open-source orchestration platform, Kubernetes processes the operations of the elastic web server framework for cloud-native apps. Websites and applications that are built on complex codes can make use of Kubernetes for efficiently reducing the cost of web servers with public cloud hosts and optimizing the software development process.
Kubernetes can effectively expand the hosting across on-premise, public/private, or hybrid clouds. This makes them a go-to platform for hosting cloud-based applications that can be scaled rapidly with real-time data streaming. Take a look at some of the reasons for the widespread popularity of Kubernetes:
- Kubernetes efficiently manages the traffic of containers. If it gets higher than usual, the load gets balanced and distributed over the network to make the deployment stable.
- It offers extreme flexibility to select a storage system from a wide list of options such as local storage, cloud storage, etc.
- Users can enjoy automatic rollouts and rollbacks by defining the desired state of their deployed containers. Moreover, the deployment process of Kubernetes along with regular removal of existing containers can be set to automatic mode.
- Users just have to assign the amount of CPU and memory (RAM) for containers and Kubernetes will automatically fit the containers for ensuring the best use of resources.
- It comes with a self-healing mode through which the failed containers get restarted, replaced, or killed in case they didn’t respond. With regular health checkups, it monitors all the container processes in real-time.
What is the Kubernetes Cluster?
A Kubernetes cluster is a collection of nodes that are used for running containerized applications. Basically, running Kubernetes simply means running a cluster. Applications get bundled up into packages along with their dependencies and are comparatively more lightweight and flexible than VMs (Virtual Machine). Therefore, Kubernetes clusters help to develop applications in less time with quick sharing and easy management.
Clusters are considered to be the heart of Kubernetes that allow users to run and schedule containers across various machines (physical, virtual, on-premises, and on the cloud). The basic components of the Kubernetes cluster are a control plane, compute machines, and nodes.
The Control plane ensures the maintenance of the desired state of clusters, for example, taking care of application container images they’re using. Whereas, nodes run all the applications and workloads.
Further, Kubernetes clusters contain one master node and several worker nodes. The master node manages the current state of a particular cluster. It is the basis of all the processes running on a cluster such as:
- Scalability and availability of applications
- Cluster state management
- Update installation
On the other hand, worker nodes are the ones responsible for running applications. They work on the tasks assigned by the master node and can be virtual machines or physical computers. An ideal Kubernetes cluster shall contain at least one master node and one worker node.
For organizing various clusters within a single physical cluster, administrators make use of namespaces. A namespace allows users to split resources of a physical cluster and share it with different teams through resource quotas.
Kubernetes Cluster Infrastructure
A Kubernetes cluster is composed of six important components. The API server, scheduler, and controller manager are utilized by the master node. Whereas, worker nodes make use of kubelet and kube-proxy. Etcd is the key-value storage placed on every node. Let’s learn about these components in brief:
- API server: It is utilized as the front-end of the Kubernetes control plane and exposes the “rest” interface of various resources.
- Scheduler: Schedules and utilizes containers as per the requirements. Also, it analyzes and selects nodes for applications to run.
- Controller Manager: It processes controller functions and defines the actual state of the cluster according to the desired specifications. Moreover, it ensures the processing of node controllers, endpoints controllers, and replication controllers.
- Kubelet: Ensures that containers are running into their dedicated pods by interacting with the Docker engine.
- Kube-proxy: Ensures regular network connectivity and work according to the rules assigned for the nodes. Also, it executes the services across all the nodes of a specific cluster.
- Etcd: It is a key-value store data that is consistent and is always ready for storing and backing the Kubernetes cluster data.
How do you Work with a Kubernetes Cluster?
Before proceeding, ensure to define the desired state of your Kubernetes cluster. The desired state will also describe the following states:
- Applications and workloads
- Application images
- Required resources
- Amount of replicas
Use the JSON or YAML files pattern for defining the desired state and specify the other necessary information. Typically, a lot of users utilize Kubernetes API for defining the desired state of the Kubernetes cluster. For this, users have to make use of the command-line (kubectl) or utilize an API for interacting with the cluster directly and set the desired state manually. Also, the master node will transfer the desired state to all the worker nodes through APIs.
For automatically aligning clusters with the desired state, Kubernetes makes use of the control plane. A control plane manages the scheduling of cluster activities and registering/responding to all the events. Moreover, it runs simultaneous and automatic control loops (or tasks) so that the cluster’s actual state matches the desired state. The tasks may include:
- Restarting containers
- Managing the replicas of a particular application
- Validating the image of containers
- Launching and managing containers
- Making regular rollouts and rollbacks
Key Terms Associated with Kubernetes Cluster
As mentioned above, a Kubernetes cluster is a set of nodes. Have a look at the below-mentioned terminology that will help you to learn and understand the functionality of the Kubernetes cluster in a better way:
1. Control plane
All the assignments regarding clusters are initiated here. It manages the worker nodes along with the Pods of a cluster. In a production environment, it runs across various computers for providing fault tolerance and more availability.
They work according to the requests placed by the control plane. A node is a worker machine that can be either a virtual or a physical machine and is managed by the master node. They can have various pods that are managed automatically by pods across the nodes.
Pods are the most basic and deployable Kubernetes object. They are used to represent the single instance of any particular process in a Kubernetes cluster. In the case of a Pod running multiple containers, all of them will be managed as a single entity and will share the resources.
It is a directory composed of all the data that is used by the container of a particular pod. Its lifetime is equal to the lifetime of the pod associated with the same. It also preserves all the data for the containers that restart.
It is a way for organizing the clusters into virtual sub-clusters mainly for the easy management of various teams or projects. There can be ‘n’ numbers of namespaces within a cluster that are logically separated from each other but are allowed to communicate at times. Namespaces cannot be nested within each other and every Kubernetes resource shall be under a single namespace. Namespaces are used to align the cluster resources among various users through resource quota.
Learning about the infrastructure and functioning of Kubernetes clusters will help you work with them more confidently. Kubernetes has helped tons of businesses across the globe to make container management more efficient. Thus, any business looking to make its software development process fast and more productive should learn Kubernetes and become familiar with the working of Kubernetes clusters.