Kubernetes Operators

#k8s

What Are Kubernetes Operators?

A Kubernetes operator is a custom controller that extends the Kubernetes API. It embeds human operational knowledge into software to automate the management of complex, stateful applications.

Imperative vs Declarative

  • In an imperative system, a human operator manually observes the current state of the system and performs specific action to reach the desired state.
  • In a declarative system, the operator defines the desired state, and the system takes care of transitioning from current state to the desired state.
  • Kubernetes follows a declarative model. Controllers continuously watches each resources' desired state (spec) and actual state (status) and run a reconciliation loop to make necessary changes and ensure the actual state matches the desired state.

Operator SDK vs. Kubebuilder

  • Both Operator SDK and Kubebulder help developers define and implement custom resources and their controllers.
  • Kubebuilder:
    • Provides minimal, Go-centric scaffolding using controller-runtime.
    • Closely aligns with core Kubernetes patterns for custom resource and controller development.
  • Operator SDK:
    • Builds on Kubebuilder’s foundation with additional features, such as:
      • Multi-language Support: Offers options to build operators using Helm or Ansible in addition to Go.
      • Enhanced Tooling: Includes built-in scorecards, streamlined testing, and a polished CLI experience.
      • OLM Integration: Simplifies deployment and upgrades in production environments through integration with the Operator Lifecycle Manager.

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