controller.go

/*
Copyright 2015 The Kubernetes Authors All rights reserved.

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/

package framework

import (
	"time"

	"github.com/GoogleCloudPlatform/kubernetes/pkg/client/cache"
	"github.com/GoogleCloudPlatform/kubernetes/pkg/runtime"
	"github.com/GoogleCloudPlatform/kubernetes/pkg/util"
)

// Config contains all the settings for a Controller.
type Config struct {
	// The queue for your objects; either a cache.FIFO or
	// a cache.DeltaFIFO. Your Process() function should accept
	// the output of this Oueue's Pop() method.
	cache.Queue

	// Something that can list and watch your objects.
	cache.ListerWatcher

	// Something that can process your objects.
	Process ProcessFunc

	// The type of your objects.
	ObjectType runtime.Object

	// Reprocess everything at least this often.
	// Note that if it takes longer for you to clear the queue than this
	// period, you will end up processing items in the order determined
	// by cache.FIFO.Replace(). Currently, this is random. If this is a
	// problem, we can change that replacement policy to append new
	// things to the end of the queue instead of replacing the entire
	// queue.
	FullResyncPeriod time.Duration

	// If true, when Process() returns an error, re-enqueue the object.
	// TODO: add interface to let you inject a delay/backoff or drop
	//       the object completely if desired. Pass the object in
	//       question to this interface as a parameter.
	RetryOnError bool
}

// ProcessFunc processes a single object.
type ProcessFunc func(obj interface{}) error

// Controller is a generic controller framework.
type Controller struct {
	config Config
}

// New makes a new Controller from the given Config.
func New(c *Config) *Controller {
	ctlr := &Controller{
		config: *c,
	}
	return ctlr
}

// Run begins processing items, and will continue until a value is sent down stopCh.
// It's an error to call Run more than once.
// Run blocks; call via go.
func (c *Controller) Run(stopCh <-chan struct{}) {
	defer util.HandleCrash()
	cache.NewReflector(
		c.config.ListerWatcher,
		c.config.ObjectType,
		c.config.Queue,
		c.config.FullResyncPeriod,
	).RunUntil(stopCh)

	util.Until(c.processLoop, time.Second, stopCh)
}

// processLoop drains the work queue.
// TODO: Consider doing the processing in parallel. This will require a little thought
// to make sure that we don't end up processing the same object multiple times
// concurrently.
func (c *Controller) processLoop() {
	for {
		obj := c.config.Queue.Pop()
		err := c.config.Process(obj)
		if err != nil {
			if c.config.RetryOnError {
				// This is the safe way to re-enqueue.
				c.config.Queue.AddIfNotPresent(obj)
			}
		}
	}
}

// ResourceEventHandler can handle notifications for events that happen to a
// resource.  The events are informational only, so you can't return an
// error.
//  * OnAdd is called when an object is added.
//  * OnUpdate is called when an object is modified. Note that oldObj is the
//      last known state of the object-- it is possible that several changes
//      were combined together, so you can't use this to see every single
//      change. OnUpdate is also called when a re-list happens, and it will
//      get called even if nothing changed. This is useful for periodically
//      evaluating or syncing something.
//  * OnDelete will get the final state of the item if it is known, otherwise
//      it will get an object of type cache.DeletedFinalStateUnknown. This can
//      happen if the watch is closed and misses the delete event and we don't
//      notice the deletion until the subsequent re-list.
type ResourceEventHandler interface {
	OnAdd(obj interface{})
	OnUpdate(oldObj, newObj interface{})
	OnDelete(obj interface{})
}

// ResourceEventHandlerFuncs is an adaptor to let you easily specify as many or
// as few of the notification functions as you want while still implementing
// ResourceEventHandler.
type ResourceEventHandlerFuncs struct {
	AddFunc    func(obj interface{})
	UpdateFunc func(oldObj, newObj interface{})
	DeleteFunc func(obj interface{})
}

// OnAdd calls AddFunc if it's not nil.
func (r ResourceEventHandlerFuncs) OnAdd(obj interface{}) {
	if r.AddFunc != nil {
		r.AddFunc(obj)
	}
}

// OnUpdate calls UpdateFunc if it's not nil.
func (r ResourceEventHandlerFuncs) OnUpdate(oldObj, newObj interface{}) {
	if r.UpdateFunc != nil {
		r.UpdateFunc(oldObj, newObj)
	}
}

// OnDelete calls DeleteFunc if it's not nil.
func (r ResourceEventHandlerFuncs) OnDelete(obj interface{}) {
	if r.DeleteFunc != nil {
		r.DeleteFunc(obj)
	}
}

// DeletionHandlingMetaNamespaceKeyFunc checks for
// cache.DeletedFinalStateUnknown objects before calling
// cache.MetaNamespaceKeyFunc.
func DeletionHandlingMetaNamespaceKeyFunc(obj interface{}) (string, error) {
	if d, ok := obj.(cache.DeletedFinalStateUnknown); ok {
		return d.Key, nil
	}
	return cache.MetaNamespaceKeyFunc(obj)
}

// NewInformer returns a cache.Store and a controller for populating the store
// while also providing event notifications. You should only used the returned
// cache.Store for Get/List operations; Add/Modify/Deletes will cause the event
// notifications to be faulty.
//
// Parameters:
//  * lw is list and watch functions for the source of the resource you want to
//    be informed of.
//  * objType is an object of the type that you expect to receive.
//  * resyncPeriod: if non-zero, will re-list this often (you will get OnUpdate
//    calls, even if nothing changed). Otherwise, re-list will be delayed as
//    long as possible (until the upstream source closes the watch or times out,
//    or you stop the controller).
//  * h is the object you want notifications sent to.
//
func NewInformer(
	lw cache.ListerWatcher,
	objType runtime.Object,
	resyncPeriod time.Duration,
	h ResourceEventHandler,
) (cache.Store, *Controller) {
	// This will hold the client state, as we know it.
	clientState := cache.NewStore(DeletionHandlingMetaNamespaceKeyFunc)

	// This will hold incoming changes. Note how we pass clientState in as a
	// KeyLister, that way resync operations will result in the correct set
	// of update/delete deltas.
	fifo := cache.NewDeltaFIFO(cache.MetaNamespaceKeyFunc, nil, clientState)

	cfg := &Config{
		Queue:            fifo,
		ListerWatcher:    lw,
		ObjectType:       objType,
		FullResyncPeriod: resyncPeriod,
		RetryOnError:     false,

		Process: func(obj interface{}) error {
			// from oldest to newest
			for _, d := range obj.(cache.Deltas) {
				switch d.Type {
				case cache.Sync, cache.Added, cache.Updated:
					if old, exists, err := clientState.Get(d.Object); err == nil && exists {
						if err := clientState.Update(d.Object); err != nil {
							return err
						}
						h.OnUpdate(old, d.Object)
					} else {
						if err := clientState.Add(d.Object); err != nil {
							return err
						}
						h.OnAdd(d.Object)
					}
				case cache.Deleted:
					if err := clientState.Delete(d.Object); err != nil {
						return err
					}
					h.OnDelete(d.Object)
				}
			}
			return nil
		},
	}
	return clientState, New(cfg)
}