Get deleted object from work queue

[tamalsaha]

We are in the process of using workqueue for our various controllers. One of the issue I see is that dequeue from workqueue does not return the object (it is nil). I understand the idea that the desired state by user is nil, after an object is deleted. But there are cases where we need access to the metadata/spec on the object. One work around I have found is to register my controller as a finalizer so I can get the object in the UpdateFunc(). One issue with finalizers is that someone can remove them by mistake. Can WorkQueue return deleted objects?

client-go/examples/workqueue/main.go

Lines 69 to 88 in c6f8cf2

	// syncToStdout is the business logic of the controller. In this controller it simply prints
	// information about the pod to stdout. In case an error happened, it has to simply return the error.
	// The retry logic should not be part of the business logic.
	func (c *Controller) syncToStdout(key string) error {
	obj, exists, err := c.indexer.GetByKey(key)
	if err != nil {
	glog.Errorf("Fetching object with key %s from store failed with %v", key, err)
	return err
	}
	if !exists {
	// Below we will warm up our cache with a Pod, so that we will see a delete for one pod
	fmt.Printf("Pod %s does not exist anymore\n", key)
	} else {
	// Note that you also have to check the uid if you have a local controlled resource, which
	// is dependent on the actual instance, to detect that a Pod was recreated with the same name
	fmt.Printf("Sync/Add/Update for Pod %s\n", obj.(*v1.Pod).GetName())
	}
	return nil
	}

[DogLi]

I'm also waiting for the answer!

[liggitt]

The queue just stores the key (typically namespace/name) of the object that changed in a way that needs to be processed. The workqueue should take the absence of the object in the store/indexer to mean the object doesn't exist and should be removed.

If you need the object, hook in at the DeleteFunc level to temporarily store the deleted object for use but be aware it is not always available (if your watch drops and gets reestablished right at deletion time you might not have the final version of the object available, or if your controller is down while an object is created and then deleted, you won't ever know it existed)

[tamalsaha]

Thank @liggitt @munnerz . I have used a separate indexer to keep track of deleted items. Here is what my modification looks like https://github.com/tamalsaha/workqueue-demo/pull/1/files . If you have any comments, please let me know in the pr.