Effective Custom Resource Definition Watching with Dynamic Informers in Go

Introduction

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

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.

Benefits of Dynamic Informers

Dynamic informers offer several advantages over traditional API clients for watching CRDs:

• Automatic code generation: They automatically generate the client code necessary to watch CRDs, eliminating the need for manual coding.
• Reduced boilerplate code: They reduce the amount of boilerplate code required to watch CRDs, making it easier to write robust controllers.
• Easier debugging: They provide improved debugging capabilities, as they automatically handle versioning and negotiation with the Kubernetes API server.
• Enhanced performance: They can significantly improve performance by reducing the number of API calls and optimizing resource caching.

Using Dynamic Informers

To use dynamic informers in Go, you can follow these steps:

1. Install the necessary libraries:

import (
    "context"
    "fmt"
    dynamic "k8s.io/client-go/dynamic"
    informer "k8s.io/client-go/informers"
)

2. Create a new dynamic client:

client, err := dynamic.NewForConfig(config)
if err != nil {
    // Handle error
}

3. Get the list of resources available:

resources, err := client.ServerResources()
if err != nil {
    // Handle error
}

4. Create a dynamic informer factory:

factory := informer.NewDynamicSharedInformerFactory(client, time.Minute*30)

5. Create an informer for the desired resource:

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.

Example

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())
}

Performance Considerations

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:

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.

Stories

Story 1

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.

Story 2

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.

Story 3

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.

Lessons Learned

The following lessons can be learned from these stories:

• Dynamic informers can significantly improve the performance of controllers by reducing the number of API calls and optimizing caching.
• Dynamic informers make it easier to watch custom CRDs, reducing the need for custom coding and improving debugging capabilities.
• Dynamic informers can be used to monitor the state of custom resources in real-time, allowing for rapid response to changes.

Effective Strategies

When using dynamic informers, it is important to consider the following strategies:

• Use the correct resource version: When watching CRDs, it is important to use the correct resource version to ensure that you receive all events. By default, dynamic informers will use the latest resource version, but you can specify a specific version if necessary.
• Handle initialization correctly: When using dynamic informers, it is important to handle initialization correctly. You should ensure that the informer is initialized before any event handlers are registered and that the informer is started before any events can be received.
• Use proper error handling: Dynamic informers can encounter various errors, so it is important to handle errors properly. You should be prepared to handle errors that occur when the informer is created, started, or during event handling.

FAQs

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.

Call to Action

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.