Custom Resource Definitions (CRDs) are a powerful mechanism in Kubernetes that allows users to define their own custom resources. Dynamic informers provide a way to watch for changes to CRDs in a dynamic and flexible manner. This article will guide you through the process of using dynamic informers to watch CRDs in Go.
Dynamic informers offer several advantages over traditional informers:
To get started, import the following packages:
import (
"context"
"github.com/kubernetes-sigs/controller-runtime/pkg/client"
"github.com/kubernetes-sigs/controller-runtime/pkg/dynamicclient"
"github.com/kubernetes-sigs/controller-runtime/pkg/informers"
)
Next, create a dynamic client to access the Kubernetes API server:
client, err := client.New(client.Options{})
if err != nil {
// Handle error
}
An informer factory is used to create dynamic informers. Create one using the dynamic client:
informerFactory := informers.NewDynamicSharedInformerFactory(client, 0)
Finally, create a dynamic informer for the desired CRD:
informer := informerFactory.ForResource(schema.GroupVersionResource{
Group: "example.com",
Version: "v1",
Resource: "foos",
})
Once the informer is created, you can watch for changes to the CRD using a channel:
ch := informer.Informer().Runs(context.Background())
The channel will receive notifications whenever an object in the CRD changes. You can handle these notifications in your controller logic.
When using dynamic informers, it is important to avoid these common mistakes:
To summarize the process:
Dynamic informers provide numerous benefits:
Story 1:
A large-scale enterprise was managing dozens of custom resources using traditional informers. This became increasingly complex and error-prone as the number of CRDs grew. By switching to dynamic informers, they were able to simplify their codebase and reduce maintenance costs.
Story 2:
A startup was developing a new controller that needed to watch multiple CRDs. Using dynamic informers allowed them to quickly get started and reduce the time spent on setting up the monitoring infrastructure.
Story 3:
A team was migrating their controller to a new platform that did not support traditional informers. By using dynamic informers, they were able to maintain the same functionality without major code changes.
Lesson: Dynamic informers offer a versatile and efficient way to watch CRDs, providing significant benefits in terms of flexibility, performance, and ease of use.
Dynamic informers are a powerful tool for monitoring Custom Resource Definitions in Kubernetes. They provide flexibility, simplified setup, and reduced boilerplate code, making them an essential part of any controller that interacts with CRDs. By embracing dynamic informers, you can streamline your application development and enhance the reliability of your custom resources.
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