Understanding Operator in Kubernetes

Author : MD TAREQ HASSAN | Updated : 2021/04/24

Operator Pattern

The Operator pattern aims to capture the key aim of a human operator who is managing a service or set of services
The Kubernetes Operator pattern acts in accordance with one of the core Kubernetes principles: the control theory
In robotics and automation, “control theory” is a mechanism that continuously operates dynamical systems

Custom Resource

Custom Resource is an extension of the Kubernetes API that provides a place where you can store and retrieve structured data—the desired state of your application
- A resource is an endpoint in the Kubernetes API that stores a collection of API objects of a certain kind
- Example: the built-in pods resource contains a collection of Pod objects
A custom resource is the API extension mechanism in Kubernetes

What is Operator?

Operators are software extensions to Kubernetes that make use of custom resources to manage applications and their components
An operator is a client of the Kubernetes API that acts as a controller for a Custom Resource
The Operator itself is a piece of software running in a Pod on the cluster, interacting with the Kubernetes API server
Operators are first class citizen in K8s
Most of the time operators are just a pod (or a few pods) running a custom controller and one or more custom resources to interact with it
An operator is a custom Kubernetes controller that uses custom resources (CR) to manage applications and their components

An operator is an application-specific controller. It extends a Kubernetes API to create, configure, and manage complex applications on behalf of humans (operation engineers or site reliability engineers). It builds upon the basic Kubernetes resource and controller concepts, but includes domain or application-specific knowledge to automate the entire life cycle of the software it manages.

Operators are mainly used for stateful applications. Using a Kubernetes operator means you can operate a stateful application by writing a custom controller with domain specific knowledge built into it.