In the previous post, Choosing a configuration method, we looked at the three ways in which a Kubernetes cluster can be configured. In this post we’ll go through the components which make up the cluster.
Kubernetes clusters have two types of servers: masters and nodes. The masters provide the control plane for the cluster while the nodes take care of the workloads. As you probably guessed, having one or more of either provides high availability.
The components documentation gives us a great rundown on the components that make up each of these two nodes, though it might be a little confusing for those who are just starting out. In this post we’ll look through each component’s documentation while adding additional information as required. Furthermore, to help really get the point across, we’ll build a diagram to show where each component resides.
In the previous post, What is it?, we gained an understanding of Kubernetes and container orchestrations in general. In this post we’ll cover the three ways in which Kubernetes can be configured.
Kubernetes’ configuration is simply a bunch of Kubernetes objects. Let’s take a quick look at what these objects are, and what they’re used for. The following quotes are from the Kubernetes object documentation:
Kubernetes Objects are persistent entities in the Kubernetes system. Kubernetes uses these entities to represent the state of your cluster. Specifically, they can describe:
- What containerized applications are running (and on which nodes)
- The resources available to those applications
- The policies around how those applications behave, such as restart policies, upgrades, and fault-tolerance
If you’ve looked into containers before, you’ve likely heard the name Kubernetes. This post will tackle what it is at a high level, while subsequent posts will delve deeper into the details.
Let’s kick off this post with a couple of quotes from the Kubernetes website:
Kubernetes is an open-source system for automating deployment, scaling, and management of containerized applications.
It groups containers that make up an application into logical units for easy management and discovery. Kubernetes builds upon 15 years of experience of running production workloads at Google, combined with best-of-breed ideas and practices from the community.
There’s a lot of great information in this quote, so let’s go ahead and take a closer look.
One server per application
In the not too distant past, it was normal to have a one to one relationship between applications and servers. For example, your mail and web applications would reside on two separate, physical servers.
This approach was greatly inefficient and costly too. Each server would be purchased with years of predicted growth in mind. This resulted in racks full of overly powerful and underutilised servers which would drive up cooling, power and data centre space costs.
Furthermore, applications would often fall short of their forecasted growth, leaving businesses in a stalemate. They would want to move their applications to smaller servers to save on costs, but they can’t guarantee they won’t break their applications in the process. If they do break, then that’ll end up costing the business too. It really was a lose-lose situation.