A Deep Dive Into Kubernetes Operators

Kubernetes has quickly become the technology of choice for delivering and managing containerized workloads and services. It has a large, rapidly growing ecosystem and provides rich features for deploying, scaling, and managing containerized applications and services. You can declaratively set up and deploy complex applications using Kubernetes in much less time than it would take to do it manually.

One of the key advancements within the Kubernetes ecosystem has been the introduction of operators. Operators provide an elegant way to extend Kubernetes’ native capabilities and automate complex application-specific tasks. Let’s explore Kubernetes Operators, why they are needed, how we can create them and the best practices around their use.

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What is Kubernetes?

With the proliferation in the adoption of DevOps culture, the need for infrastructure that can be rapidly built, scaled, and secured has become a necessity. The Kubernetes container orchestration framework has become the de facto standard for the orchestration of containers in today’s rapidly changing technology landscape. As a result of its ability to automate the deployment, scaling and management of applications, it has revolutionized the way organizations build and manage their infrastructure.

Kubernetes, also known as K8s, is an open source, portable, extensible and cloud-agnostic container orchestration platform for automating container scaling, deployment and management containers, which are systems that run virtualized applications. It provides abstractions for scheduling, controlling and managing containerized applications across cluster resources. The adoption of Kubernetes is increasing as developers see it as a powerful tool that can streamline their workflow and reduce their time spent on infrastructure management.

What are Kubernetes Operators?

A Kubernetes Operator is a unique controller to an application and extends the Kubernetes API to allow you to create and manage instances of a complex application. You can take advantage of the idea of a resource and a controller from Kubernetes and add domain-specific information to automate the life cycle of an application. Kubernetes operators help you to package, manage and deploy Kubernetes applications.

A Kubernetes Operator includes:

• A custom resource definition (CRD)
• A custom resource
• A controller

Key Features of Kubernetes Operators

The key features of Kubernetes Operators include the following:

• Automated deployment and scaling
• CRDs
• Self-healing capabilities
• Support for custom controllers
• Configuration management
• Support for extensibility
• Kubernetes Operators extend Kubernetes functionality
• Kubernetes Operators are cluster-agnostic
• Built-in support for monitoring and observability

Benefits of Kubernetes Operators

• Automation: Operators use automated processes to reduce manual interventions needed to maintain complex applications. This way, they can address issues such as provisioning, scaling and troubleshooting so that the application runs independently.
• Customization: Operators have specific requirements based on the application they manage. Developers can use this concept to create operators tailored to their applications’ specific needs, giving them greater control over the behavior of their applications.
• Consistency: Operators can promote consistency by abstracting away from the specifics of the underlying infrastructure. The benefits of this type of deployment are that the application behaves consistently across different Kubernetes clusters and environments.
• Self-healing: A self-healing application can detect and fix deviations by continuously matching the desired state with the actual state, making the application more resilient and self-repairing.
• Community support: Kubernetes is powered by the community, which develops and actively maintains a set of operators for popular applications and databases. Using this rich ecosystem, users can benefit from the experience and expertise of the broader user community.

How Does a Kubernetes Operator Work?

• Defining a CRD is the first step. With a CRD, you can create a new type of resource in Kubernetes that is specific to the application or workload you want to manage. A CRD describes the structure and schema of an application or workload.
• The next step is to create a custom controller that monitors changes in custom resources in the Kubernetes cluster. It monitors the Kubernetes API server for events related to the custom resources, such as create, update or delete events.
• In response to events triggered by custom resources, the custom controller executes the reconciliation loop. By reconciling the state of the application with the desired state, we can ensure that the actual state is identical to the desired state. The reconciliation loop kicks in when the custom controller detects a change in the custom resource.
• The Operator decides what actions to take based on the comparison between the desired state and the actual state. As an example, if the desired replica count exceeds the current replica count, the Operator will add more replicas.
• The Operator interacts with the Kubernetes API server to align the application’s actual state with the desired state. As needed, Kubernetes resources are created, updated or deleted.
• The reconciliation loop ensures the application’s state remains in sync with the desired state. To maintain the desired configuration, it watches for changes in the cluster.
• An Operator should include logic to handle failures and recoveries. When a pod in the application crashes, the operator can automatically replace it to restore the application’s desired state.

Figure 1: Kubernetes Operators at work!

Challenges of Kubernetes Operators

Despite the benefits of Kubernetes Operators, there are several challenges, as well.

• Complexity: Building Kubernetes operators is quite complex and there is a steep learning curve.
• Error handling: It can be quite challenging to handle errors and retries, especially when you’re working with complex applications.
• Version compatibility: Kubernetes has been evolving quickly and steadily. This explains why maintaining versioning compatibility with different Kubernetes versions can be a challenge.
• Upgrade and rollback: It is quite challenging to ensure compatibility with different operator versions and maintain backward compatibility.
• Cluster-specific configuration: Kubernetes operators must be flexible enough to accommodate various cluster configurations, security policies and resource restrictions.
• Testing: You should have comprehensive tests in place for your operators, such as unit tests, integration tests, etc.

The Kubernetes Operator Framework

The Kubernetes Operator Framework encompasses a collection of tools and libraries used to build, maintain and deploy Kubernetes operators. This enables you to build reusable, consistent and easy-to-manage solutions for managing complex applications and workloads on Kubernetes clusters in a consistent, reusable and easy-to-manage manner.

The primary objective of the operator framework is to help establish a high-quality, community-driven operator ecosystem, which is crucial to the surge in popularity and growth of Kubernetes.

The Kubernetes Operator Framework includes three components:

• Operator SDK
• Operator life cycle manager
• Operator SDK Ansible

In Kubernetes, operators are represented as custom controllers and extend the Kubernetes API with enhanced resources and include the necessary custom logic for managing them. For example, a database operator might create a custom resource named database, which represents a database instance and includes the necessary custom logic for creating and maintaining instances of the resource.

Creating a Kubernetes Operator

To create a custom Kubernetes Operator, follow the steps outlined below:

1. Define a CRD for the resource you would like to manage
2. Write your custom controller that can watch for instances of the resource
3. Build the operator using the Operator SDK
4. Create an instance of the resource using kubectl

Best Practices

While creating Kubernetes Operators, there are several best practices you should follow:

• Develop one Operator per application
• Use asynchronous sync loops
• Adopt a test-driven development approach
• Use the Operator SDK
• Use declarative APIs
• Avoid overstuffed functions
• Wrap external dependencies

Conclusion

With the explosive adoption of containers, especially in the last few years, it has become evident that an effective and standard way to manage these types of applications is needed. Kubernetes was created as a platform for automating the deployment, scaling, management and maintenance of containerized applications.

To summarize, here’s how a Kubernetes operator’s workflow works:

1. Define a CRD
2. The user makes changes to the CRD
3. The Operator keeps track of the CRD and identifies any changes that occur
4. The Operator carries out a reconciliation process between the CRD and the desired state
5. The Operator adjusts the cluster state to the desired state