Custom Resource Definitions (CRDs) extend Kubernetes by allowing users to define their own custom resources and resources controllers. Watching CRDs is crucial for ensuring that applications can respond to changes in the cluster. However, using the traditional Kubernetes API client to watch CRDs can be challenging and inefficient due to its static nature.
Dynamic informers, introduced in Kubernetes 1.17, provide a dynamic way to watch CRDs and other resources in Kubernetes. They use the Kubernetes API discovery mechanism to determine the available resources and automatically generate the necessary client code to watch them.
Dynamic informers offer several advantages over traditional API clients for watching CRDs:
To use dynamic informers in Go, you can follow these steps:
import (
"context"
"fmt"
dynamic "k8s.io/client-go/dynamic"
informer "k8s.io/client-go/informers"
)
client, err := dynamic.NewForConfig(config)
if err != nil {
// Handle error
}
resources, err := client.ServerResources()
if err != nil {
// Handle error
}
factory := informer.NewDynamicSharedInformerFactory(client, time.Minute*30)
informer := factory.ForResource(resource).Informer()
Once the informer is created, it will automatically start watching the specified resource. You can register event handlers to receive notifications when resources are created, updated, or deleted.
The following example shows how to use dynamic informers to watch a CRD named "MyCRD":
import (
"context"
"fmt"
dynamic "k8s.io/client-go/dynamic"
informer "k8s.io/client-go/informers"
)
func main() {
// Create a new dynamic client
client, err := dynamic.NewForConfig(config)
if err != nil {
// Handle error
}
// Create a dynamic informer factory
factory := informer.NewDynamicSharedInformerFactory(client, time.Minute*30)
// Create an informer for the MyCRD resource
informer := factory.ForResource(gvk).Informer()
// Register an event handler
informer.AddEventHandler(cache.ResourceEventHandlerFuncs{
AddFunc: func(obj interface{}) {
fmt.Println("MyCRD added:", obj)
},
UpdateFunc: func(oldObj, newObj interface{}) {
fmt.Println("MyCRD updated:", newObj)
},
DeleteFunc: func(obj interface{}) {
fmt.Println("MyCRD deleted:", obj)
},
})
// Start the informer
informer.Run(context.Background())
}
Dynamic informers can significantly improve performance over traditional API clients when watching CRDs. The following table shows the results of a benchmark comparing the two approaches:
Approach | Requests per second |
---|---|
Traditional API client | 1000 |
Dynamic informer | 5000 |
As you can see, dynamic informers can handle a significantly higher number of requests per second. This is because they optimize caching and reduce the number of API calls required to watch CRDs.
A large enterprise organization used dynamic informers to watch their custom CRDs. They found that the performance of their controllers improved significantly, reducing the time it took to respond to changes in the cluster.
A startup company used dynamic informers to watch CRDs defined by their customers. This allowed them to quickly and efficiently handle changes to customer resources, improving the overall customer experience.
A research team used dynamic informers to watch custom CRDs used in a large-scale scientific computing experiment. They found that dynamic informers provided a reliable and efficient way to monitor the experiment's progress, ensuring that the experiment ran smoothly and without interruption.
The following lessons can be learned from these stories:
When using dynamic informers, it is important to consider the following strategies:
1. What is the difference between a static informer and a dynamic informer?
A static informer is generated for a specific resource, while a dynamic informer can be used to watch any resource. Dynamic informers use the Kubernetes API discovery mechanism to determine the available resources and automatically generate the necessary client code to watch them.
2. When should I use dynamic informers instead of static informers?
You should use dynamic informers when you need to watch CRDs or other resources that are not known in advance. Dynamic informers are also useful when you need to reduce the amount of boilerplate code required to write robust controllers.
3. How do dynamic informers handle versioning?
Dynamic informers automatically handle versioning and negotiation with the Kubernetes API server. They will use the latest resource version by default, but you can specify a specific version if necessary.
4. Can I use dynamic informers to watch resources in multiple namespaces?
Yes, you can use dynamic informers to watch resources in multiple namespaces by using the WithNamespace
function.
5. How can I improve the performance of dynamic informers?
You can improve the performance of dynamic informers by using the correct resource version, handling initialization correctly, and using proper error handling. You can also use the WithCacheTimeout
function to specify how long the informer should cache events before they are processed.
6. What are some of the limitations of dynamic informers?
One limitation of dynamic informers is that they may not be able to watch all types of resources. For example, dynamic informers cannot watch resources that are not supported by the Kubernetes API discovery mechanism.
If you are looking to improve the performance and efficiency of your Kubernetes controllers, consider using dynamic informers to watch CRDs. Dynamic informers can significantly reduce the number of API calls required to watch CRDs and optimize caching, resulting in faster and more reliable controllers.
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