In Kubernetes, Custom Resource Definitions (CRDs) allow you to extend Kubernetes capabilities by defining your own resources. Monitoring changes to these CRDs is vital for maintaining the health and performance of your applications. Using a single informer to watch multiple CRD changes can significantly streamline your monitoring process. In this article, we will explore how to achieve this efficiently.
What is an Informer?
An informer in Kubernetes is a client-side cache that watches for changes to a specified resource type (like CRDs) and maintains an up-to-date copy of that resource in memory. Informers significantly reduce the load on the Kubernetes API server by minimizing the number of calls required to fetch the current state of resources.
Benefits of Using a Single Informer
- Efficiency: Instead of creating multiple informers for each CRD, a single informer reduces resource consumption and API server load.
- Simplicity: Fewer informers lead to simpler code management and a cleaner architecture.
- Consistency: Monitoring multiple resources through a unified structure provides a consistent interface and behavior.
Steps to Monitor Multiple CRD Changes with a Single Informer
Step 1: Define Your CRDs
Before you start using an informer, make sure you have your CRDs defined. For example, consider two CRDs, Foo and Bar.
Step 2: Create an Informer
You can create an informer for your CRDs by using the Kubernetes client-go library. Here’s a simplified example in Go:
import (
"context"
"k8s.io/apimachinery/pkg/runtime/schema"
"k8s.io/client-go/tools/cache"
"k8s.io/client-go/kubernetes/scheme"
"k8s.io/client-go/tools/clientcmd"
"k8s.io/apimachinery/pkg/runtime"
"k8s.io/client-go/kubernetes"
)
// Define your GroupVersion for CRDs
var fooGroupVersion = schema.GroupVersion{Group: "example.com", Version: "v1"}
var barGroupVersion = schema.GroupVersion{Group: "example.com", Version: "v1"}
func main() {
// Load kubeconfig and create client
config, _ := clientcmd.BuildConfigFromFlags("", "/path/to/kubeconfig")
clientset, _ := kubernetes.NewForConfig(config)
// Create shared informer factory
informerFactory := informers.NewSharedInformerFactory(clientset, time.Second*30)
// Create informers for each CRD type
fooInformer := informerFactory.ForResource(fooGroupVersion.WithResource("foos")).Informer()
barInformer := informerFactory.ForResource(barGroupVersion.WithResource("bars")).Informer()
// Use a single event handler for both informers
handler := cache.ResourceEventHandlerFuncs{
AddFunc: handleAdd,
UpdateFunc: handleUpdate,
DeleteFunc: handleDelete,
}
fooInformer.AddEventHandler(handler)
barInformer.AddEventHandler(handler)
// Start informers
stopCh := make(chan struct{})
defer close(stopCh)
informerFactory.Start(stopCh)
// Block forever
select {}
}
Step 3: Implement Event Handlers
Define the logic you want to execute when CRD events occur. You can use the same handler for both Foo and Bar CRDs:
func handleAdd(obj interface{}) {
// Handle the addition of a new resource
fmt.Println("Resource added:", obj)
}
func handleUpdate(oldObj, newObj interface{}) {
// Handle updates to a resource
fmt.Println("Resource updated:", newObj)
}
func handleDelete(obj interface{}) {
// Handle the deletion of a resource
fmt.Println("Resource deleted:", obj)
}
Step 4: Start the Informers
With the informers set up and the event handlers defined, you can start the informers, and they will listen for changes to both Foo and Bar CRDs.
Conclusion
Using a single informer to monitor multiple CRDs in Kubernetes can lead to a more efficient and manageable system. By following the steps outlined in this article, you can implement a solution that effectively tracks changes across different custom resources, simplifying your Kubernetes resource management and enhancing application reliability.
This approach also illustrates the flexibility of the Kubernetes client-go library, which provides powerful tools for handling custom resources and events seamlessly.
