Kubernetes Objects Vs Resources Vs Custom Resource

In the ever-evolving landscape of container orchestration, Kubernetes has emerged as the de facto standard. As developers and operators delve into the intricacies of Kubernetes, they often encounter terms like "Objects," "Resources," and "Custom Resources." This article aims to demystify these concepts, providing a clear understanding of their roles within the Kubernetes ecosystem.

Understanding Kubernetes Objects:
Kubernetes objects are the fundamental entities that represent the state of your cluster. These objects define what gets deployed, where it gets deployed, and how it is configured. Examples of Kubernetes objects include pods, services, deployments, and more. Each object encapsulates a set of properties that define its behavior within the cluster.

Kubernetes Resources:
In the context of Kubernetes, resources refer to the compute, memory, and storage requirements that a pod or container needs to run successfully. When you define resource requirements for a pod, Kubernetes uses this information to schedule and allocate appropriate resources on the cluster nodes. Let's look at an example command to set resource limits for a pod:

kubectl create deployment nginx --image=nginx --limits=cpu=500m,memory=512Mi

In this example, we create a deployment named "nginx" with specified resource limits for CPU and memory.

Custom Resources in Kubernetes:
Custom Resources (CRs) extend the Kubernetes API to enable users to define and manage their custom objects. These objects are not part of the default Kubernetes installation but are added by users to tailor the Kubernetes experience to their specific needs. To illustrate, let's create a simple Custom Resource Definition (CRD) and a custom resource using the following commands:

# Create a Custom Resource Definition (CRD)
kubectl apply -f custom-resource-definition.yaml

# Create an instance of the Custom Resource
kubectl apply -f custom-resource-instance.yaml

Here, the "custom-resource-definition.yaml" file defines the structure of the custom resource, while the "custom-resource-instance.yaml" file creates an actual instance of that custom resource.

Objects vs Resources vs Custom Resources: A Comparison:

• Objects: These are the building blocks of the Kubernetes system, representing the desired state of the system.
• Resources: Refers to the computational units (CPU, memory) allocated to pods for optimal functioning.
• Custom Resources: User-defined objects that extend the Kubernetes API, providing a way to introduce bespoke functionality.

Examples in Real-world Scenarios:
To further illustrate these concepts, let's consider a scenario where you want to deploy a multi-tier application using Kubernetes objects, allocate specific resources to each pod, and introduce a custom resource to manage application-specific configurations.

Step-by-Step Instructions:

1. Define Kubernetes objects such as deployments, services, and pods for each tier of the application.
2. Specify resource requirements for each pod to ensure efficient resource utilization.
3. Create a Custom Resource Definition (CRD) to represent application-specific configurations.
4. Instantiate a custom resource based on the defined CRD to manage the application's unique settings.

By following these steps, you can orchestrate a complex application, leveraging the power of Kubernetes objects, resources, and custom resources.