Core Concepts

This section covers the fundamental building blocks of Kubernetes that you need to understand for the CKA exam. We’ll explore the key resources that make up a Kubernetes application and how they work together.

What You’ll Learn

  • Pods: The smallest deployable units in Kubernetes that host your application containers
  • ReplicaSets: Ensure a specified number of pod replicas are running at any given time
  • Replication Controllers: The predecessor to ReplicaSets, providing basic pod replication
  • Deployments: Higher-level resources that manage ReplicaSets and provide declarative updates
  • Services: Networking abstractions that expose applications running on pods
  • Namespaces: Virtual clusters that provide isolation and organization within a Kubernetes cluster

Declarative vs. Imperative Approaches

Kubernetes supports two primary approaches to resource management:

Imperative Commands

With the imperative approach, you directly tell Kubernetes what to do using specific commands:

kubectl run nginx --image=nginx
kubectl create deployment nginx --image=nginx
kubectl expose deployment nginx --port=80

Advantages:

  • Quick for simple tasks
  • Good for learning
  • Useful for troubleshooting

Disadvantages:

  • Difficult to track changes
  • Not suitable for complex applications
  • Harder to automate and version control

Declarative Configuration

With the declarative approach, you define the desired state of resources in YAML or JSON files:

kubectl apply -f deployment.yaml
kubectl apply -f service.yaml

Advantages:

  • Configuration is documented and version-controlled
  • Supports complex deployments
  • Easier to audit and review
  • Ideal for GitOps workflows

Disadvantages:

  • Steeper learning curve
  • Requires understanding YAML/JSON syntax

In real-world production environments, the declarative approach is strongly recommended, but knowing both approaches is valuable for the CKA exam.

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