What is a Kubernetes Operator?

An operator is an extension of Kubernetes that uses resources to automatically manage applications and their components. Operators are typically built as a set of independent controllers, where each is responsible for its own subset of resources and tasks. They encode specialized knowledge about applications to automate deployment, scaling, upgrades, and more for complex applications running on Kubernetes clusters.

Operators do not require custom resources, although they very often work with those. There are also operators that work with built-in resource types that come standard with Kubernetes out-of-the-box.

Operators add extra functionality to Kubernetes for managing specific applications that have multiple components which need coordination. For example, a Postgres operator helps run PostgreSQL databases on Kubernetes by handling tasks like provisioning, failover, and backups automatically. 

Operators follow the "operator pattern" where they constantly watch for certain resources and then perform actions to reach or maintain a desired state. This makes them ideal for deploying and running stateful services like databases, caches and monitoring systems.

By leveraging native Kubernetes approaches like control loops, resource management and health checks, operators simplify running production-grade applications on Kubernetes. 

Now that we know what Kubernetes operators are, let's explore some of the major benefits of using operators to manage applications:

Operators encode deep application knowledge to extend Kubernetes' built-in capabilities for provisioning, auto-scaling, upgrades, failover and more. They handle complex tasks like:

• Automated provisioning of storage, configs and credentials
• Streamlined scaling up or down based on metrics like load, memory consumption or average request latency
• Graceful handling of failovers and cluster restarts
• Automated background upgrades and patching

By focusing on administrative best practices and implementing them directly into software, operators will simplify lifecycle management.

Operators provide a unified control plane to deploy and manage applications across on-premise, multi-cloud, edge, and hybrid environments. They abstract infrastructure complexity by:

• Using Kubernetes APIs across heterogeneous environments
• Transferring applications across cloud providers
• Unifying policy management in centralized control plane
• Deploying to edge devices seamlessly

This makes hybrid deployments smoother.

By leveraging native Kubernetes APIs and resources like the control loop, operators minimize how much custom YAML you need to write. They simplify automation by:

• Handling app lifecycles automatically
• Taking over repeatable processes like scaling Kubernetes deployments
• Encapsulating domain expertise in code
• Leveraging health checks and status updates

Operators enhance Kubernetes, reducing manual operations. These richer advantages of deployment automation, smooth hybrid cloud portability and simplified app management make operators a very useful tool for running production workloads.

Next we'll explore how operators achieve this by working with Kubernetes API

Kubernetes controllers and operators are both extensions of the control plane that automate tasks, but they differ in scope and complexity.

Kubernetes controllers are control loops that watch the state of the cluster via the API server and make changes to drive the actual state towards the desired state. They handle common tasks like replicating pods, tracking node assignments, handling rolling updates, and maintaining the desired number of nodes.

Controllers use a declarative model where you specify the desired state in API objects, and the controllers do the work to make that state happen. The Kubernetes controller manager runs a set of default controllers like replication controller, endpoints controller, namespace controller, etc.

Operators, on the other hand, are custom Kubernetes controllers that use custom resources to manage applications and their components. They extend the Kubernetes control plane by allowing you to define application-specific controllers for complex stateful applications.

An operator encapsulates human operational knowledge into software, reducing the effort of running complex applications on Kubernetes. It can perform app-specific tasks like:

• Deploying an application on demand
• Taking and restoring backups of application state
• Handling upgrades for an application
• Simulating failure in all or part of cluster for testing

Operators allow you to define a desired state for your application using custom resources - the operator then continuously takes action to reach and maintain this state. This can involve complex workflows like provisioning infrastructure, setting up monitoring, taking backups, coordinating upgrades, etc.

In essence, operators are an extension of the controller pattern that allows capturing more complex, app-specific workflows beyond the generic functionality Kubernetes controllers provide. By combining general Kubernetes controllers with application-specific operators, you can achieve end-to-end automation of complex applications running on Kubernetes.

Next, we'll contrast operators with another common Kubernetes pattern - Helm charts.

Helm streamlines installing and upgrading applications on Kubernetes through packaging formats like charts, templating, and version management. Helm focuses on the initial deployment of applications.

In contrast, operators focus more on the ongoing lifecycle after applications have been deployed. Operators pick up where Helm charts leave off to automate repetitive management tasks like:

• Auto-scaling based on load metrics
• Ensuring upgraded versions don't break apps
• Remediating failures and ensuring high availability

Together Helm and operators provide complementary capabilities for application management lifecycle. Helm handles templated deployments while operators manage complex day-2 operations.

By extending native Kubernetes APIs, encoding domain expertise into specialist controllers, and integrating with Kubernetes resources like jobs, statefulsets and RBAC, operators build on Kubernetes to simplify previously complex application management for stateful services.

Next we'll look at some real-world examples of popular Kubernetes operators used by cloud native organizations globally.

We've understood how operators work. Let's explore some popular real-world operators used by organizations:

Kong Gateway Operator - Provides a Kubernetes-native way to deploy and manage Kong Gateway on Kubernetes clusters. It allows users to deploy and configure Kong Gateway using Kubernetes Custom Resource Definitions (CRDs) instead of traditional tools like Helm.

RBAC Manager Operator - Simplifies Role-Based Access Control (RBAC) management on Kubernetes clusters by centralizing user permission policies instead of individual namespaces. It automates complex tasks like policy reconciliation, user group management, and audit logging.

HPA Operator - The Horizontal Pod Autoscaler (HPA) Operator manages and automates pod auto-scaling across namespaces using Kubernetes-native HorizontalPodAutoscaler resources. It scales pods based on metrics and ensures availability during surges.

Istio Operator - This operator simplifies installation, upgrade, and lifecycle management of Istio's service mesh capabilities directly on Kubernetes clusters. It automates tasks like traffic flow control, security policy configuration, certificate management, and more.

Elastic Cloud on Kubernetes - This operator deploys and manages complex Elasticsearch clusters on Kubernetes by automating provisioning, scaling, upgrades, retries and failure recovery across various environments like public cloud and on-premise.

Grafana Operator - Makes deploying and managing Grafana analytics and monitoring dashboards on Kubernetes simple through automation of Grafana instances, associated datastores, dashboard and datasource configuration along with seamless upgrades.

These demonstrate how operators encapsulate complex application knowledge to automate provisioning, high availability, scalability, upgrades and more - making Kubernetes much easier for running business-critical systems.

Next we will provide a quick overview of building your own custom operators.

While several operators exist, you may also build your own custom operator for specific applications using frameworks like:

Operator SDK

This is an open source toolkit to facilitate building Kubernetes native operators in Golang, Ansible, or Helm. It handles boilerplate code and uses controller-runtime libraries to simplify development. The SDK provides high level APIs and abstractions for common operator tasks. It supports multiple languages and frameworks while integrating well with Kubernetes ecosystem tools.

Kubebuilder

It is a framework to construct Kubernetes APIs and operators for core resources and external services by extending the Kubernetes control plane. It provides code generation and custom resource validation. Kubebuilder generates CRDs, controllers, admission webhooks etc. It provides a testing harness and tooling while integrating with RBAC, aggregated APIs for easier extension.

Key steps to build an operator involve:

1. Defining Custom Resources - The first step is defining new CustomResourceDefinitions (CRDs) that model your application architecture as custom resources. This involves designing the CRD schema, OpenAPI validation, and versioning the CRD definitions appropriately.
2. Implementing Controllers - Next, you implement controllers to observe, analyze and reconcile the desired state for custom resources. This requires initializing clients to access Kubernetes APIs, implementing reconcile loops to compare desired vs actual state and performing CRUD operations to update resources.
3. Adding Application Logic - With the core controller in place, you add application domain logic, workflows and orchestration. This can include provisioning app instances, configurations, storage etc., managing upgrades, scaling, high availability, handling failures, restarts, backups and more.
4. Testing and Packaging - Rigorous testing and validation of the operator is crucial before deployment. This spans unit testing, integration testing and validation with tools like OPA Gatekeeper. Finally, the operator is packaged and distributed using common tools like OLM.
5. Defining Installations - The last step is defining installations and upgrades for the operator in a declarative way using Helm charts, YAML manifests etc. This allows easy discovery and installation by leveraging tools like OLM.

Using operators involves deploying them into Kubernetes clusters through manifests so they can watch over applications via custom resources. Common workflows include:

1. Installing CRDs - The first step is installing the custom resource definitions to extend the Kubernetes API and allow creating instances of the custom resources.
2. Deploying Operator - Next, the operator deployment, RBAC rules etc. are applied to the cluster. This starts up the operator to begin watching custom resources.
3. Creating App Instances - With the operator deployed, you can create instances of the custom resources for each application you want the operator to manage.
4. Updating App Instances - During the app lifecycle, you modify the custom resource instances to trigger the operator to reconcile the app to the desired state - deploying updates, scaling replicas, performing failovers etc.

By bridging intimate application knowledge with Kubernetes automation capabilities, operators greatly simplify app deployment and lifecycle management - making them a key part of the cloud-native ecosystem.

Kubernetes has become the standard for container orchestration, but running stateful, production-grade services on it remains challenging. This is where Kubernetes operators come in. They automate complex application management by encoding admin logic into software directly.

We covered how operators extend Kubernetes functionality by integrating with its control plane and API server to manage applications via custom resources. Operators contain application domain knowledge to simplify tasks like auto-scaling, upgrades, failovers, and more.

Compared to manual workflows or general Kubernetes configuration, operators provide a simpler and more robust way of deploying and managing stateful applications on Kubernetes. That means reduced operations overhead, increased resilience, and hybrid/multi-cloud portability.

As Kubernetes becomes the runtime across environments from cloud to edge, operators will play a pivotal role in making application management easier. They simplify automation for entire application lifecycles. By leveraging operators, organizations can reduce operational complexity and make the most of Kubernetes.

Continued Learning & Related Content

• Painless Kong Gateway Upgrades on Kubernetes with the Kong Gateway Operator
• Introducing Kong Gateway Operator
• Introducing the World’s First OSS Production-Grade Gateway API Operator

• Kubernetes Operators vs HELM: Package Management Comparison
• What's the Difference: Kubernetes Controllers vs Operators?
• Guide to Understanding Kubernetes Deployments

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• What is a Kubernetes Ingress Controller?
• What is Kubernetes?
• Understanding The Basics of Kubernetes Architecture