Kubernetes client-go use Informers to watch deployments

I'm trying to use client-go informers to get the replica count on deployments. Whenever autoscaling changes the number of replicas, I need to retrieve this in order to handle some other logic. I was previously using the Watch() function, but there are a few inconsistencies with timeouts and connection drops.

The following code below shows an example of the implementation:

labelOptions := informers.WithTweakListOptions(func(opts *v1.ListOptions) {
    opts.FieldSelector = "metadata.name=" + name
})
factory := informers.NewSharedInformerFactoryWithOptions(clientSet, 2*time.Second, informers.WithNamespace(namespace), labelOptions)
informer := factory.Apps().V1().Deployments().Informer()

// Using the channels and goroutines below didn't show changes:
stopper := make(chan struct{})
defer close(stopper)
//go func() {
informer.AddEventHandler(cache.ResourceEventHandlerFuncs{
    AddFunc: func(obj interface{}) {
        mObj, ok := obj.(*appsv1.Deployment)
        if !ok {
            panic(spew.Sdump("informer returned invalid type", mObj))
        }

        replicas := int(*mObj.Spec.Replicas)
        logger.Infof("updating replicas to %d", replicas)

        sendUpdates() // use updates elsewhere
    },

    
    UpdateFunc: func(oldObj, newObj interface{}) {
        old, ok := oldObj.(*appsv1.Deployment)
        if !ok {
            panic(spew.Sdump("informer returned invalid type", old))
        }
        newDeployment, ok := newObj.(*appsv1.Deployment)
        if !ok {
            panic(spew.Sdump("informer returned invalid type", newDeployment))
        }
        oldReplicas := int(*old.Spec.Replicas)
        newReplicas := int(*newDeployment.Spec.Replicas)
        if oldReplicas != newReplicas {
            sendUpdates()
        }
    },
})

//factory.Start(wait.NeverStop)
//factory.WaitForCacheSync(wait.NeverStop)
informer.Run(stopper)

When Kubernetes autoscales or I change the Deployments replica manually, I get deployment.apps/app scaled but it doesn't get caught by the Informer. Nothing gets printed in the logs and it enters a crash loop with no error message.

I used the following resources:

Solution

A few things to note:

Before calling informerFactory.Start(), ensure that the Informer is called directly(informer := factory.Apps().V1().Deployments().Informer()) or Start() wont start anything.
Using a goroutine to start the SharedInformerFactory is meaningless because the informerFactory.Start() uses one internally.
It will also cease the informerFactory.WaitForCacheSync() method from working resulting in it getting the wrong data for started informers.

labelOptions := informers.WithTweakListOptions(func(opts *v1.ListOptions) {
    opts.FieldSelector = "metadata.name=" + name
})
factory := informers.NewSharedInformerFactoryWithOptions(clientSet, 2*time.Second, informers.WithNamespace(namespace), labelOptions)
informer := factory.Apps().V1().Deployments().Informer()

informer.AddEventHandler(cache.ResourceEventHandlerFuncs{
    AddFunc: func(obj interface{}) {
        mObj, ok := obj.(*appsv1.Deployment)
        if !ok {
            doSomething()
        }
        replicas := int(*mObj.Spec.Replicas)
        doSomething() 
    },

    
    UpdateFunc: func(oldObj, newObj interface{}) {
        old, ok := oldObj.(*appsv1.Deployment)
        if !ok {
            doSomething()
        }
        newDeployment, ok := newObj.(*appsv1.Deployment)
        if !ok {
            doSomething()
        }
        oldReplicas := int(*old.Spec.Replicas)
        newReplicas := int(*newDeployment.Spec.Replicas)
        if oldReplicas != newReplicas {
            doSomething()
        }
    },
})

// Initializes all active informers and starts the internal goroutine
factory.Start(wait.NeverStop)
factory.WaitForCacheSync(wait.NeverStop)