Siddharth Kushwaha

KUBERNETES

INTRODUCTION

Official site - Kubernetes (K8s) is an open-source system for automating deployment, scaling, and management of containerized applications.

Red Hat - Kubernetes, or k8s (k, 8 characters, s...get it?), or “kube” if you’re into brevity, is an open source platform that automates Linux container operations. It eliminates many of the manual processes involved in deploying and scaling containerized applications. In other words, you can cluster together groups of hosts running Linux containers, and Kubernetes helps you easily and efficiently manage those clusters. These clusters can span hosts across public, private, or hybrid clouds. For this reason, Kubernetes is an ideal platform for hosting cloud-native applications that require rapid scaling, like real-time data streaming through Apache Kafka.

Digital Ocean - Kubernetes is a powerful open-source system, initially developed by Google, for managing containerized applications in a clustered environment. It aims to provide better ways of managing related, distributed components and services across varied infrastructure.

Let’s take a look at why Kubernetes is so useful by going back in time.

Traditional deployment era: Early on, organizations ran applications on physical servers. There was no way to define resource boundaries for applications in a physical server, and this caused resource allocation issues. For example, if multiple applications run on a physical server, there can be instances where one application would take up most of the resources, and as a result, the other applications would underperform. A solution for this would be to run each application on a different physical server. But this did not scale as resources were underutilized, and it was expensive for organizations to maintain many physical servers.

Virtualized deployment era: As a solution, virtualization was introduced. It allows you to run multiple Virtual Machines (VMs) on a single physical server’s CPU. Virtualization allows applications to be isolated between VMs and provides a level of security as the information of one application cannot be freely accessed by another application.

Virtualization allows better utilization of resources in a physical server and allows better scalability because an application can be added or updated easily, reduces hardware costs, and much more. With virtualization you can present a set of physical resources as a cluster of disposable virtual machines.

Each VM is a full machine running all the components, including its own operating system, on top of the virtualized hardware.

Container deployment era: Containers are similar to VMs, but they have relaxed isolation properties to share the Operating System (OS) among the applications. Therefore, containers are considered lightweight. Similar to a VM, a container has its own filesystem, CPU, memory, process space, and more. As they are decoupled from the underlying infrastructure, they are portable across clouds and OS distributions.

Containers have become popular because they provide extra benefits, such as:

• Agile application creation and deployment: increased ease and efficiency of container image creation compared to VM image use.
• Continuous development, integration, and deployment: provides for reliable and frequent container image build and deployment with quick and easy rollbacks (due to image immutability).
• Dev and Ops separation of concerns: create application container images at build/release time rather than deployment time, thereby decoupling applications from infrastructure.
• Observability not only surfaces OS-level information and metrics, but also application health and other signals.
• Environmental consistency across development, testing, and production: Runs the same on a laptop as it does in the cloud.
• Cloud and OS distribution portability: Runs on Ubuntu, RHEL, CoreOS, on-prem, Google Kubernetes Engine, and anywhere else.
• Application-centric management: Raises the level of abstraction from running an OS on virtual hardware to running an application on an OS using logical resources.
• Loosely coupled, distributed, elastic, liberated micro-services: applications are broken into smaller, independent pieces and can be deployed and managed dynamically – not a monolithic stack running on one big single-purpose machine.
• Resource isolation: predictable application performance.
• Resource utilization: high efficiency and density.

What can you do with Kubernetes?

The primary advantage of using Kubernetes in your environment, especially if you are optimizing app dev for the cloud, is that it gives you the platform to schedule and run containers on clusters of physical or virtual machines. More broadly, it helps you fully implement and rely on a container-based infrastructure in production environments. And because Kubernetes is all about automation of operational tasks, you can do many of the same things that other application platforms or management systems let you do, but for your containers.

With Kubernetes you can:

• Orchestrate containers across multiple hosts.
• Make better use of hardware to maximize resources needed to run your enterprise apps.
• Control and automate application deployments and updates.
• Mount and add storage to run stateful apps.
• Scale containerized applications and their resources on the fly.
• Declaratively manage services, which guarantees the deployed applications are always running how you deployed them.
• Health-check and self-heal your apps with autoplacement, autorestart, autoreplication, and autoscaling.

Kubernetes, however, relies on other projects to fully provide these orchestrated services. With the addition of other open source projects, you can fully realize the power of Kubernetes. These necessary pieces include (among others):

• Registry, through projects like Atomic Registry or Docker Registry.
• Networking, through projects like OpenvSwitch and intelligent edge routing.
• Telemetry, through projects such as heapster, kibana, hawkular, and elastic.
• Security, through projects like LDAP, SELinux, RBAC, and OAUTH with multi-tenancy layers.
• Automation, with the addition of Ansible playbooks for installation and cluster life-cycle management.
• Services, through a rich catalog of precreated content of popular app patterns.

Learn to speak Kubernetes

Like any technology, there are a lot of words specific to the technology that can be a barrier to entry. Let's break down some of the more common terms to help you understand Kubernetes.

Master: The machine that controls Kubernetes nodes. This is where all task assignments originate.

Node: These machines perform the requested, assigned tasks. The Kubernetes master controls them.

Pod: A group of one or more containers deployed to a single node. All containers in a pod share an IP address, IPC, hostname, and other resources. Pods abstract network and storage away from the underlying container. This lets you move containers around the cluster more easily.

Replication controller:  This controls how many identical copies of a pod should be running somewhere on the cluster.

Service: This decouples work definitions from the pods. Kubernetes service proxies automatically get service requests to the right pod—no matter where it moves to in the cluster or even if it’s been replaced.

Kubelet: This service runs on nodes and reads the container manifests and ensures the defined containers are started and running.

kubectl: This is the command line configuration tool for Kubernetes.

Conclusion

Kubernetes is an exciting project that allows users to run scalable, highly available containerized workloads on a highly abstracted platform. While Kubernetes’ architecture and set of internal components can at first seem daunting, their power, flexibility, and robust feature set are unparalleled in the open-source world. By understanding how the basic building blocks fit together, you can begin to design systems that fully leverage the capabilities of the platform to run and manage your workloads at scale.