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What is a Kubernetes Operator?

A Kubernetes operator is a method of packaging, deploying, and managing a Kubernetes application. Kubernetes applications are deployed and managed on Kubernetes using the Kubernetes Application Programming Interface (API) and kubectl tooling.

A Kubernetes Operator is an application-specific controller that extends the functionality of the Kubernetes API to create, configure and manage instances of complex applications for a Kubernetes user.

General Kubernetes concepts for resources and controllers are used for this purpose. However, domain or application-specific knowledge is also required to automate the entire lifecycle of the managed software.

In Kubernetes, controllers in the control plane implement control loops that repeatedly compare the desired and current status of the cluster with one another. If the current state of the cluster does not match the desired state, the controller takes action to correct the problem.

An operator is a custom Kubernetes controller that uses Custom Resources (CR) to manage applications and their components. General configuration and settings are provided by the user in a CR. The Kubernetes Operator translates the general instructions into individual actions based on the best practices embedded in its logic.

Custom Resources are the API extension mechanisms in Kubernetes. A Custom Resource Definition (CRD) defines a CR and lists all configurations available to the user of the operator.

The Kubernetes Operator monitors the CR type and initiates application-specific actions to adapt the current status of the resource to the desired status.

With the help of Kubernetes Operators, new object types are made available in the form of Custom Resource Definitions. Custom Resource Definitions can be treated like integrated objects with the Kubernetes API, including the interaction via kubectl and the integration into RBCA guidelines (Role-based Access Control).

Kubernetes Operators monitor applications as they run and can automatically back up data, restore the system after errors and continuously upgrade applications.

Virtually any imaginable action can be performed with a Kubernetes operator: scaling complex apps, upgrading the application version, and even managing kernel modules for nodes in a computing cluster with specialized hardware.

Learn more about how Kubernetes Operators work, including practical examples, and how to build them using the Operator Framework and Software Development Kits.

How operators manage Kubernetes applications

Kubernetes can be used to manage and scale stateless applications, such as web applications, mobile backends, and API services, without the need for additional knowledge of how these applications work. The built-in features of Kubernetes are designed to make these tasks easy to handle.

However, stateful applications such as databases and monitoring systems require additional domain-specific information that Kubernetes does not have. This information is required to scale, upgrade, and reconfigure these applications.

Using Kubernetes Operators, this domain-specific information is encoded into Kubernetes extensions so that the application lifecycle can be managed and automated.

By eliminating complex manual application management tasks, Kubernetes Operators ensure that these processes are scalable, repeatable, and standardized.

They do this by making it easy for developers to deploy and run the basic services that their apps depend on.

These operators provide infrastructure engineers and vendors with a consistent way to distribute software across Kubernetes clusters and reduce the amount of support work by identifying and correcting application problems.

Operators allow you to write task automation code well beyond the basic automation features of Kubernetes. Teams using a DevOps or Site Reliability Engineering (SRE) approach can use Operators to integrate SRE practices with Kubernetes.

The function of the operator pattern is to mimic the management of a service by a human operator. A human operator needs to know exactly how apps or services work, how they are provided and how to resolve any problems that may arise.

Typically, functional safety engineers or operations teams write the software to manage an application. An operator, on the other hand, is designed to encode human operational knowledge into software to manage and provision Kubernetes workloads, eliminating manual tasks.

Operators should preferably be developed by someone who has a thorough understanding of the business logic behind installing, running, and upgrading a particular application.

Often times, creating an operator begins with automating installation and self-service provisioning of the application, followed by more complex automation functions.

There is also a handy Operator SDK (Software Development Kit) that you can use to develop your own Kubernetes Operators. The SDK provides the tools for creating, testing and packaging operators, optionally with Helm Charts, Ansible Playbooks or Golang.

Operator Framework

The Operator Framework is an open source project with developer and runtime tools for Kubernetes that you can use to accelerate the development of an operator.

The operator framework includes the following:

  • Operator SDK: Allows developers to create operators based on their expertise without having to be familiar with the complexities of the Kubernetes API.
  • Operator lifecycle management: Monitors the installation, updates and management of the lifecycle of all operators running in a Kubernetes cluster.
  • Operator measurement: Allows usage reports for operators who provide specific services.

Use Operators in Red Hat OpenShift

Red Hat® OpenShift® is an enterprise-grade Kubernetes container platform that automates operations across the stack to make it easier to manage hybrid and multi-clouds.

Red Hat OpenShift uses Kubernetes Operators to run the entire platform autonomously and at the same time reveals the configuration natively via Kubernetes objects, which in turn enables fast installation and frequent, robust updates.

Red Hat OpenShift includes the embedded OperatorHub, a registry of certified operators from software providers and open source projects. Within the OperatorHub, you can browse and install a library of Operators that are Red Hat OpenShift compatible and packaged for easy lifecycle management.