K
Q

SharedInformerFactoryWithOptions - Not able to filter based on labels

11/3/2021

I want to watch Kubernetes pod events for a certain application.

I went with NewSharedInformerFactoryWithOptions. I have added appropriate labels selector, But it is not getting filtered out. As I want to filter it using the label: 'app=nats-box'

Here is the code - 

req, err := labels.NewRequirement("app", selection.Equals, []string{"nats-box"})
	if err != nil {
		log.Fatalf("error %s, bad requirement", err.Error())
	}
selector := labels.NewSelector()
selector.Add(*req)

filteredFactory := informers.NewSharedInformerFactoryWithOptions(clientset, 0, informers.WithNamespace("default"), informers.WithTweakListOptions(func(options *metav1.ListOptions) {
	options.LabelSelector = selector.String()
}))

podInformer := filteredFactory.Core().V1().Pods().Informer()

podInformer.AddEventHandler(cache.ResourceEventHandlerFuncs{
	AddFunc: func(obj interface{}) {
		fmt.Println("pod add")
		name := obj.(*corev1.Pod).Name
		labels := obj.(*corev1.Pod).Labels
		fmt.Printf("pod Name: %s\nLabels - %v\n\n", name, labels)
	})

I get the output for all the pods, the namespace is getting filtered but not the labels. Not able to figure out where I am making the mistake.

-- ankit
client-go
go
kubernetes

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2 Answers

4/15/2022

If you want to keep using the k8s.io/apimachinery/pkg/labels and selection packages, you need to re-assign selector when calling selector.Add because it returns a copy.

So, replace 

selector := labels.NewSelector()
selector.Add(*req)
fmt.Println(selector.String()) // empty string

with

selector := labels.NewSelector()
selector = selector.Add(*req)
fmt.Println(selector.String()) // app=nats-box
-- Letik
Source: StackOverflow
11/3/2021

You can directly provide the label string in the opts.LabelSelector:

labelOptions := informers.WithTweakListOptions(func(opts *metav1.ListOptions) {
	opts.LabelSelector = "app=nats-box"
})
factory := informers.NewSharedInformerFactoryWithOptions(clientset, 0, informers.WithNamespace("default") ,labelOptions)
informer := factory.Core().V1().Pods().Informer()
stopper := make(chan struct{})
defer close(stopper)
informer.AddEventHandler(cache.ResourceEventHandlerFuncs{
	AddFunc: func(obj interface{}) {
		fmt.Println("pod add")
		name := obj.(*corev1.Pod).Name
		labels := obj.(*corev1.Pod).Labels
		fmt.Printf("pod Name: %s\nLabels - %v\n\n", name, labels)
	},
})
informer.Run(stopper)
-- Theofilos Papapanagiotou
Source: StackOverflow