Introduction

Custom Resource Definitions (CRDs) are a powerful feature of Kubernetes that extends its API to allow users to define their custom resources and controllers. When combined with Helm, a package manager for Kubernetes, CRDs enable users to streamline the deployment and management of custom resources alongside their applications. In this article, we'll explore CRDs in Helm, provide an example to illustrate their usage and discuss their benefits in Kubernetes environments.

Understanding CRDs in Helm

CRDs in Helm enable users to define and manage custom resources within Helm charts, allowing for greater flexibility and customization in Kubernetes deployments. CRDs are typically included in Helm charts alongside other Kubernetes resources, and Helm facilitates the deployment and management of these custom resources alongside the main application components.

Example: Deploying a Custom Resource with Helm

Let's consider an example where we want to deploy a custom resource named MyCustomResource using Helm:

1. Define the Custom Resource Definition (CRD)

   First, we define the CRD for MyCustomResource in a YAML file, mycustomresource-crd.yaml:

    apiVersion: apiextensions.k8s.io/v1
    kind: CustomResourceDefinition
    metadata:
      name: mycustomresources.example.com
    spec:
      group: example.com
      names:
        kind: MyCustomResource
        plural: mycustomresources
        singular: mycustomresource
      scope: Namespaced
      versions:
        - name: v1
          served: true
          storage: true
   

   This CRD definition specifies the group, kind, and version of the custom resource, along with its scope (Namespaced or Cluster).

2. Create the Helm Chart

   Next, we create a Helm chart named my-custom-resource:

    helm create my-custom-resource
   

3. Include the CRD in the Helm Chart

   We include the CRD YAML file (mycustomresource-crd.yaml) in the templates directory of the Helm chart.

4. Deploy the Helm Chart

   Finally, we deploy the Helm chart to Kubernetes:

    helm install my-custom-resource ./my-custom-resource
   

Benefits of CRDs in Helm

1. Customization: CRDs enable users to define custom resources tailored to their specific application requirements, allowing for greater customization and flexibility in Kubernetes deployments.

2. Abstraction: By abstracting custom resources into Helm charts, users can easily manage and deploy complex applications consisting of both standard Kubernetes resources and custom resources.

3. Reusability: Helm charts containing CRDs can be shared and reused across different projects, promoting consistency and standardization in Kubernetes deployments.

4. Automation: Helm simplifies the deployment and management of CRDs alongside other Kubernetes resources, enabling the automation of complex application workflows.

Conclusion

Custom Resource Definitions (CRDs) in Helm offer a powerful mechanism for extending Kubernetes with custom resources tailored to specific application needs. By combining Helm's package management capabilities with CRDs, users can streamline the deployment and management of custom resources alongside their applications, leading to greater customization, reusability, and automation in Kubernetes environments. Whether deploying simple microservices or complex distributed systems, CRDs in Helm empower users to leverage the full potential of Kubernetes for their unique use cases.