An Introduction to Kubernetes for Beginners

When it comes to developing, delivering and maintaining containerized applications in a clustered environment, at scale, across a wide number of physical and virtual machines, Kubernetes becomes the savior technology that developers resort to.

Initially created and used internally by Google for over a decade, Kubernetes became open source and publicly accessible in 2014. Ever since, it has become the de facto standard for deploying, distributing and managing applications that have a number of microservices and need to coordinate on a cluster of machines. It uses methods that foster scalability, predictability and high availability for managing the lifecycle of containerized applications. Kubernetes has emerged as the ruling platform for developing machine learning models.

Kubernetes gives you the freedom to decide how the application runs and how different containers communicate and interact with each other. You can easily scale up the application when you add new features or when the traffic goes up. Kubernetes also lets you easily perform rolling updates, switch traffic between different versions and use multiple interfaces and platforms for managing applications. Any problematic Deployments can easily be rolled back, providing you complete flexibility over application lifecycle management

To understand how Kubernetes does all of this with such apparent ease and aplomb, we need to understand the basic architecture of Kubernetes. We need to get an idea of how Kubernetes is designed and what are the various components of it.

At the most basic level, Kubernetes brings together a network of physical or virtual machines known as nodes, to form a cluster that is governed by a master server. Here are the most important elements of the Kubernetes system:

Containers

Kubernetes uses Linux containers to host the programs. The primary job of Kubernetes is to manage, deploy and monitor these containers. The containers can contain pre-built images that are easily downloadable in the client’s device. These can be packed and shared across the internet in one single file. Deployment is made extremely simple with containers as they require minimal setup to run applications in isolation and with flexibility.

Nodes

A node is essentially a host that runs your applications or cloud workflows. It can either be a physical or a virtual machine that resides in a cluster and is responsible for running workloads with the help of external resources. Each node contains all the services required to run an application like container runtime, kube-proxy and kubelet. You don’t normally interact with nodes directly, as the Kubernetes master controls each node.

Cluster

The real strength of Kubernetes cluster orchestration system lies in clusters. A cluster is simply a collection of multiple nodes, with at least one cluster master. The Kubernetes master is a collection of processes that maintains the desired state of the cluster. This small unit however, ensures that the application runs smoothly even if an individual node malfunctions. Once a program is deployed on the cluster, the cluster automatically handles distribution. If any node is added or removed in the process, it doesn’t affect the application as the cluster manager the work as needed.

Pod

A Pod is the smallest and simplest unit that you can create or deploy in Kubernetes. This is the first part of the running process on your cluster, and it encapsulates an application container, storage resources, unique network IP and other options that decide how a container should run. It can be a single container or a few containers that share resources. Kubernetes, instead of running the containers directly, wraps up multiple containers into a pod. These pods can replicate themselves and even be configured to deploy new replicas of the pod as the application scales. So when the application starts garnering more traffic and one pod can’t take the load, Kubernetes can deploy new replicas of the pod as needed.

Kubernetes, unlike other containerization technologies, is unique in the way that it does not run individual containers directly. Instead, it wraps a few containers into a pod, so that these containers use the same local network and the same resources. This enables these pods to communicate with each other easily even in an isolated state.

It is notable here that though pods are capable of holding multiple containers, limiting to one or two containers per pod facilitates a more optimal use of resources.

Master Server

The master server, as mentioned above, acts as the brain or the primary gateway of the Kubernetes clusters. It works as the main contact point for both app users and administrators. It manages the workload and controls the clusters as per the incoming server requests. It schedules workloads, authenticates clients, performs health checks, manages scaling and adjusts networking across clusters.

Deployment

So now we know that pods are the basic functional units in Kubernetes that need to be launched on to the cluster. Doing so however involves one or more layers of abstraction. Once your cluster is up and running, it’s time to deploy the containerized application on it. So you begin by describing a desired state in your deployment object and the deployment controller takes over. It changes the current actual state to the desired state in a controlled environment. You can now define Deployments depending on your application goals and new replica sets are created to meet the desired deployment.

Deployments are usually used to rollout, adjust and manage ReplicaSets, declare new state of the pods, scale up or scale down the deployment to meet changing needs and clean up older ReplicaSets you don’t use any longer. The great thing about using Kubernetes is that once you declare the state of the system, every object kicks into action automatically and you don’t need to deal with individual pods, nodes or clusters. Thanks to all these capabilities, Deployments are the Kubernetes object you will work with most of the time.

Wrapping Up

You’re already feeling excited about Kubernetes, aren’t you? It is definitely an exciting platform to work with, knowing how scalable, highly available and abstracted it is. At first, the Kubernetes architecture with its niche elements like nodes, pods and clusters may seem daunting, but once you take the first steps, the rest begins to fall in place by itself as you progress.

Kubernetes has been adopted by some of the largest public cloud vendors and technology providers in the world. Thanks to its flawless design, industry leading collaborations and open source natures, Kubernetes is definitely the future of containerized application management.