Lesson 3: Kubernetes Concepts and High Availability

In this lesson, you will learn the basics of Kubernetes, its core components, and the principles of high availability. Furthremore, you will understand how these concepts apply to the cluster you’ll build in this guide.

This is the 3rd lesson of the guide Building a production-ready Kubernetes cluster from scratch. Make sure you have completed the previous lesson before continuing here. The full list of lessons in the guide can be found in the overview.

Before we dive into building our Kubernetes cluster, it’s essential to understand the key concepts that underpin Kubernetes and high availability, to establish a solid foundation and knowledge on terminology for the rest of the guide.

What is Kubernetes?

Kubernetes is an open-source platform for automating the deployment, scaling, and management of containerized applications. Originally developed by Google, Kubernetes has become the de-facto standard for large-scale container orchestration, allowing you to run and manage your applications across a cluster of servers efficiently.

At its core, Kubernetes groups containers that make up an application into logical units for easy management and discovery. It automates the deployment and operation of application containers across clusters of hosts, providing mechanisms for deployment, maintenance, and scaling.

Key Components of Kubernetes

Kubernetes consists of several key components:

• The Kubernetes Control Plane manages the state of the cluster, making global decisions about the cluster (like scheduling) and detecting and responding to cluster events (like starting up new pods when a deployment’s replicas field is unsatisfied).
• The Kubelet is an agent that runs on each node in the cluster. It ensures that containers are running in a pod as expected.
• The Pod is the smallest and simplest Kubernetes object. A pod represents a single instance of a running process in your cluster and can contain one or more containers.
• Kube-Proxy is a network proxy that runs on each node in the cluster. It maintains network rules on nodes, allowing network communication to your pods from network sessions inside or outside of your cluster.
• The etcd component is a consistent and highly available key-value store used as Kubernetes’ backing store for all cluster data.
• Kubernetes API Server is the front end for the Kubernetes control plane. It exposes the Kubernetes API, which lets you interact with your cluster.
• Kubernetes Scheduler watches for newly created pods with no assigned node and selects a node for them to run on.
• Container Runtime is the software that is responsible for running containers. Kubernetes supports several container runtimes, including Docker, containerd, and CRI-O.
• Storage Provisioner automates the creation and management of storage resources for your cluster. It dynamically provisions storage volumes when requested by users, ensuring that applications have the necessary storage available without manual intervention.

What is High Availability (HA)?

High Availability (HA) refers to the ability of a system to remain operational and accessible even in the presence of faults or failures. In the context of Kubernetes, HA ensures that your cluster remains functional even when one or more components fail. This is achieved by:

• Deploying multiple instances of critical components, such as the control plane and etcd, across different nodes to eliminate single points of failure.
• Using load balancers to distribute traffic evenly across these components, ensuring that the cluster continues to respond to client requests even if some instances go down.
• Implementing redundant networking and storage configurations to maintain data integrity and network connectivity during failures.

Why High Availability is Important for Kubernetes

High availability is critical for any production environment because it minimizes downtime and ensures consistent access to applications and services. In Kubernetes, high availability protects against hardware failures, software bugs, and other unexpected issues that could otherwise lead to service disruptions.

For example, if one of your control plane nodes fails, a high-availability configuration with multiple control plane nodes will continue to function without any downtime. This is essential for applications that require continuous uptime or have high service-level agreements (SLAs).

Applying These Concepts to Your Raspberry Pi Cluster

Throughout this guide, we will build a high-availability Kubernetes cluster using Raspberry Pi devices. You will learn to set up multiple control plane nodes, configure etcd for fault tolerance, and use load balancers to distribute traffic. By the end of this guide, you will have a robust cluster that can handle real-world scenarios and continue running even when faced with challenges.

Lesson Conclusion

Congratulations! You have completed this lesson and you can now continue with the next one.