k8s garbage collector分析（1）-啟動分析
garbage collector介紹
Kubernetes garbage collector即垃圾收集器，存在於kube-controller-manger中，它負責回收kubernetes中的資源對象，監聽資源對象事件，更新對象之間的依賴關系，並根據對象的刪除策略來決定是否刪除其關聯對象。
關於刪除關聯對象，細一點說就是，使用級聯刪除策略去刪除一個owner時，會連帶這個owner對象的dependent對象也一起刪除掉。
關於對象的關聯依賴關系，garbage collector會監聽資源對象事件，根據資源對象中ownerReference 的值，來構建對象間的關聯依賴關系，也即owner與dependent之間的關系。
關於owner與dependent的介紹
以創建deployment對象為例進行講解。
創建deployment對象后，kube-controller-manager為其創建出replicaset對象，且自動將該deployment的信息設置到replicaset對象ownerReference值。如下面示例，即說明replicaset對象test-1-59d7f45ffb的owner為deployment對象test-1，deployment對象test-1的dependent為replicaset對象test-1-59d7f45ffb。
apiVersion: apps/v1
kind: Deployment
metadata:
name: test-1
namespace: test
uid: 4973d370-3221-46a7-8d86-e145bf9ad0ce
...
apiVersion: apps/v1
kind: ReplicaSet
metadata:
name: test-1-59d7f45ffb
namespace: test
ownerReferences:
- apiVersion: apps/v1
blockOwnerDeletion: true
controller: true
kind: Deployment
name: test-1
uid: 4973d370-3221-46a7-8d86-e145bf9ad0ce
uid: 386c380b-490e-470b-a33f-7d5b0bf945fb
...
同理，replicaset對象創建后，kube-controller-manager為其創建出pod對象，這些pod對象也會將replicaset對象的信息設置到pod對象的ownerReference的值中，replicaset是pod的owner，pod是replicaset的dependent。
對象中ownerReference 的值，指定了owner與dependent之間的關系。
garbage collector架構圖
garbage collector中最關鍵的代碼就是garbagecollector.go與graph_builder.go兩部分。
garbage collector的主要組成為1個圖（對象關聯依賴關系圖）、2個處理器（GraphBuilder與GarbageCollector）、3個事件隊列（graphChanges、attemptToDelete與attemptToOrphan）：
1個圖
（1）uidToNode：對象關聯依賴關系圖，由GraphBuilder維護，維護着所有對象間的關聯依賴關系。在該圖里，每一個k8s對象會對應着關系圖里的一個node，而每個node都會維護一個owner列表以及dependent列表。
示例：現有一個deployment A，replicaset B（owner為deployment A），pod C（owner為replicaset B），則對象關聯依賴關系如下：
3個node，分別是A、B、C
A對應一個node，無owner，dependent列表里有B；
B對應一個node，owner列表里有A，dependent列表里有C；
C對應一個node，owner列表里有B，無dependent。
2個處理器
（1）GraphBuilder：負責維護所有對象的關聯依賴關系圖，並產生事件觸發GarbageCollector執行對象回收刪除操作。GraphBuilder從graphChanges事件隊列中獲取事件進行消費，根據資源對象中ownerReference的值，來構建、更新、刪除對象間的關聯依賴關系圖，也即owner與dependent之間的關系圖，然后再作為生產者生產事件，放入attemptToDelete或attemptToOrphan隊列中，觸發GarbageCollector執行，看是否需要進行關聯對象的回收刪除操作，而GarbageCollector進行對象的回收刪除操作時會依賴於uidToNode這個關系圖。
（2）GarbageCollector：負責回收刪除對象。GarbageCollector作為消費者，從attemptToDelete與attemptToOrphan隊列中取出事件進行處理，若一個對象被刪除，且其刪除策略為級聯刪除，則進行關聯對象的回收刪除。關於刪除關聯對象，細一點說就是，使用級聯刪除策略去刪除一個owner時，會連帶這個owner對象的dependent對象也一起刪除掉。
3個事件隊列
（1）graphChanges：list/watch apiserver，獲取事件，由informer生產，由GraphBuilder消費；
（2）attemptToDelete：級聯刪除事件隊列，由GraphBuilder生產，由GarbageCollector消費；
（3）attemptToOrphan：孤兒刪除事件隊列，由GraphBuilder生產，由GarbageCollector消費。
garbage collector相關啟動參數分析
kcm組件啟動參數中，與garbage collector相關的參數代碼如下：
// cmd/kube-controller-manager/app/options/garbagecollectorcontroller.go
// AddFlags adds flags related to GarbageCollectorController for controller manager to the specified FlagSet.
func (o *GarbageCollectorControllerOptions) AddFlags(fs *pflag.FlagSet) {
if o == nil {
return
}
fs.Int32Var(&o.ConcurrentGCSyncs, "concurrent-gc-syncs", o.ConcurrentGCSyncs, "The number of garbage collector workers that are allowed to sync concurrently.")
fs.BoolVar(&o.EnableGarbageCollector, "enable-garbage-collector", o.EnableGarbageCollector, "Enables the generic garbage collector. MUST be synced with the corresponding flag of the kube-apiserver.")
}
從代碼中可以看到，kcm組件啟動參數中有兩個參數與garbage collector相關，分別是：
（1）enable-garbage-collector：是否開啟garbage collector，默認值為true；
（2）concurrent-gc-syncs：garbage collector同步操作的worker數量，默認20。
garbage collector的源碼分析將分成兩部分進行，分別是：
（1）啟動分析；
（2）核心處理邏輯分析。
本篇博客先對garbage collector進行啟動分析。
garbage collector源碼分析-啟動分析
基於tag v1.17.4
https://github.com/kubernetes/kubernetes/releases/tag/v1.17.4
直接以startGarbageCollectorController函數作為garbage collector的源碼分析入口。
startGarbageCollectorController
startGarbageCollectorController函數主要邏輯如下：
（1）根據EnableGarbageCollector變量的值來決定是否開啟garbage collector，EnableGarbageCollector變量的值根據kcm組件啟動參數--enable-garbage-collector配置獲取，默認為true；不開啟則直接返回，不會繼續往下執行；
（2）初始化discoveryClient，主要用來獲取集群中的所有資源對象；
（3）調用garbagecollector.GetDeletableResources，獲取集群內garbage collector需要處理去刪除回收的所有資源對象，支持delete, list, watch三種操作的資源對象稱為 deletableResource；
（4）調用garbagecollector.NewGarbageCollector初始化garbage collector；
（5）調用garbageCollector.Run，啟動garbage collector；
（6）調用garbageCollector.Sync監聽集群中的deletableResources ，當出現新的deletableResources時同步到monitors中，確保監控集群中的所有資源；
（7）暴露http服務，注冊 debug 接口，用於debug，用來提供由GraphBuilder構建的集群內所有對象的關聯關系。
// cmd/kube-controller-manager/app/core.go
func startGarbageCollectorController(ctx ControllerContext) (http.Handler, bool, error) {
if !ctx.ComponentConfig.GarbageCollectorController.EnableGarbageCollector {
return nil, false, nil
}
gcClientset := ctx.ClientBuilder.ClientOrDie("generic-garbage-collector")
discoveryClient := cacheddiscovery.NewMemCacheClient(gcClientset.Discovery())
config := ctx.ClientBuilder.ConfigOrDie("generic-garbage-collector")
metadataClient, err := metadata.NewForConfig(config)
if err != nil {
return nil, true, err
}
// Get an initial set of deletable resources to prime the garbage collector.
deletableResources := garbagecollector.GetDeletableResources(discoveryClient)
ignoredResources := make(map[schema.GroupResource]struct{})
for _, r := range ctx.ComponentConfig.GarbageCollectorController.GCIgnoredResources {
ignoredResources[schema.GroupResource{Group: r.Group, Resource: r.Resource}] = struct{}{}
}
garbageCollector, err := garbagecollector.NewGarbageCollector(
metadataClient,
ctx.RESTMapper,
deletableResources,
ignoredResources,
ctx.ObjectOrMetadataInformerFactory,
ctx.InformersStarted,
)
if err != nil {
return nil, true, fmt.Errorf("failed to start the generic garbage collector: %v", err)
}
// Start the garbage collector.
workers := int(ctx.ComponentConfig.GarbageCollectorController.ConcurrentGCSyncs)
go garbageCollector.Run(workers, ctx.Stop)
// Periodically refresh the RESTMapper with new discovery information and sync
// the garbage collector.
go garbageCollector.Sync(gcClientset.Discovery(), 30*time.Second, ctx.Stop)
return garbagecollector.NewDebugHandler(garbageCollector), true, nil
}
下面對startGarbageCollectorController函數里的部分邏輯稍微展開一下分析。
1.garbagecollector.NewGarbageCollector
NewGarbageCollector函數負責初始化garbage collector。主要邏輯如下：
（1）初始化GarbageCollector結構體；
（2）初始化GraphBuilder結構體，並賦值給GarbageCollector結構體的dependencyGraphBuilder屬性。
// pkg/controller/garbagecollector/garbagecollector.go
func NewGarbageCollector(
metadataClient metadata.Interface,
mapper resettableRESTMapper,
deletableResources map[schema.GroupVersionResource]struct{},
ignoredResources map[schema.GroupResource]struct{},
sharedInformers controller.InformerFactory,
informersStarted <-chan struct{},
) (*GarbageCollector, error) {
attemptToDelete := workqueue.NewNamedRateLimitingQueue(workqueue.DefaultControllerRateLimiter(), "garbage_collector_attempt_to_delete")
attemptToOrphan := workqueue.NewNamedRateLimitingQueue(workqueue.DefaultControllerRateLimiter(), "garbage_collector_attempt_to_orphan")
absentOwnerCache := NewUIDCache(500)
gc := &GarbageCollector{
metadataClient: metadataClient,
restMapper: mapper,
attemptToDelete: attemptToDelete,
attemptToOrphan: attemptToOrphan,
absentOwnerCache: absentOwnerCache,
}
gb := &GraphBuilder{
metadataClient: metadataClient,
informersStarted: informersStarted,
restMapper: mapper,
graphChanges: workqueue.NewNamedRateLimitingQueue(workqueue.DefaultControllerRateLimiter(), "garbage_collector_graph_changes"),
uidToNode: &concurrentUIDToNode{
uidToNode: make(map[types.UID]*node),
},
attemptToDelete: attemptToDelete,
attemptToOrphan: attemptToOrphan,
absentOwnerCache: absentOwnerCache,
sharedInformers: sharedInformers,
ignoredResources: ignoredResources,
}
if err := gb.syncMonitors(deletableResources); err != nil {
utilruntime.HandleError(fmt.Errorf("failed to sync all monitors: %v", err))
}
gc.dependencyGraphBuilder = gb
return gc, nil
}
1.1 gb.syncMonitors
gb.syncMonitors的主要作用是調用gb.controllerFor對各個deletableResources（deletableResources指支持 “delete”, “list”, “watch” 三種操作的資源對象）資源對象的infomer做初始化，並為資源的變化事件注冊eventHandler（AddFunc、UpdateFunc 和 DeleteFunc），對於資源的add、update、delete event，都會push到graphChanges隊列中，然后gb.processGraphChanges會從graphChanges隊列中取出event進行處理（后面介紹garbage collector處理邏輯的時候會做詳細分析）。
// pkg/controller/garbagecollector/graph_builder.go
func (gb *GraphBuilder) syncMonitors(resources map[schema.GroupVersionResource]struct{}) error {
gb.monitorLock.Lock()
defer gb.monitorLock.Unlock()
toRemove := gb.monitors
if toRemove == nil {
toRemove = monitors{}
}
current := monitors{}
errs := []error{}
kept := 0
added := 0
for resource := range resources {
if _, ok := gb.ignoredResources[resource.GroupResource()]; ok {
continue
}
if m, ok := toRemove[resource]; ok {
current[resource] = m
delete(toRemove, resource)
kept++
continue
}
kind, err := gb.restMapper.KindFor(resource)
if err != nil {
errs = append(errs, fmt.Errorf("couldn't look up resource %q: %v", resource, err))
continue
}
c, s, err := gb.controllerFor(resource, kind)
if err != nil {
errs = append(errs, fmt.Errorf("couldn't start monitor for resource %q: %v", resource, err))
continue
}
current[resource] = &monitor{store: s, controller: c}
added++
}
gb.monitors = current
for _, monitor := range toRemove {
if monitor.stopCh != nil {
close(monitor.stopCh)
}
}
klog.V(4).Infof("synced monitors; added %d, kept %d, removed %d", added, kept, len(toRemove))
// NewAggregate returns nil if errs is 0-length
return utilerrors.NewAggregate(errs)
}
gb.controllerFor
gb.controllerFor主要是對資源對象的infomer做初始化，並為資源的變化事件注冊eventHandler（AddFunc、UpdateFunc 和 DeleteFunc），對於資源的add、update、delete event，都會push到graphChanges隊列中。
// pkg/controller/garbagecollector/graph_builder.go
func (gb *GraphBuilder) controllerFor(resource schema.GroupVersionResource, kind schema.GroupVersionKind) (cache.Controller, cache.Store, error) {
handlers := cache.ResourceEventHandlerFuncs{
// add the event to the dependencyGraphBuilder's graphChanges.
AddFunc: func(obj interface{}) {
event := &event{
eventType: addEvent,
obj: obj,
gvk: kind,
}
gb.graphChanges.Add(event)
},
UpdateFunc: func(oldObj, newObj interface{}) {
// TODO: check if there are differences in the ownerRefs,
// finalizers, and DeletionTimestamp; if not, ignore the update.
event := &event{
eventType: updateEvent,
obj: newObj,
oldObj: oldObj,
gvk: kind,
}
gb.graphChanges.Add(event)
},
DeleteFunc: func(obj interface{}) {
// delta fifo may wrap the object in a cache.DeletedFinalStateUnknown, unwrap it
if deletedFinalStateUnknown, ok := obj.(cache.DeletedFinalStateUnknown); ok {
obj = deletedFinalStateUnknown.Obj
}
event := &event{
eventType: deleteEvent,
obj: obj,
gvk: kind,
}
gb.graphChanges.Add(event)
},
}
shared, err := gb.sharedInformers.ForResource(resource)
if err != nil {
klog.V(4).Infof("unable to use a shared informer for resource %q, kind %q: %v", resource.String(), kind.String(), err)
return nil, nil, err
}
klog.V(4).Infof("using a shared informer for resource %q, kind %q", resource.String(), kind.String())
// need to clone because it's from a shared cache
shared.Informer().AddEventHandlerWithResyncPeriod(handlers, ResourceResyncTime)
return shared.Informer().GetController(), shared.Informer().GetStore(), nil
}
2.garbageCollector.Run
garbageCollector.Run負責啟動garbage collector，主要邏輯如下：
（1）調用gc.dependencyGraphBuilder.Run：啟動GraphBuilder；
（2）根據啟動參數配置的worker數量，起相應數量的goroutine，執行gc.runAttemptToDeleteWorker與gc.runAttemptToOrphanWorker，兩者屬於GarbageCollector的核心處理邏輯，都是去刪除需要被回收對象，具體分析會在下篇博客里進行分析。
// pkg/controller/garbagecollector/garbagecollector.go
func (gc *GarbageCollector) Run(workers int, stopCh <-chan struct{}) {
defer utilruntime.HandleCrash()
defer gc.attemptToDelete.ShutDown()
defer gc.attemptToOrphan.ShutDown()
defer gc.dependencyGraphBuilder.graphChanges.ShutDown()
klog.Infof("Starting garbage collector controller")
defer klog.Infof("Shutting down garbage collector controller")
go gc.dependencyGraphBuilder.Run(stopCh)
if !cache.WaitForNamedCacheSync("garbage collector", stopCh, gc.dependencyGraphBuilder.IsSynced) {
return
}
klog.Infof("Garbage collector: all resource monitors have synced. Proceeding to collect garbage")
// gc workers
for i := 0; i < workers; i++ {
go wait.Until(gc.runAttemptToDeleteWorker, 1*time.Second, stopCh)
go wait.Until(gc.runAttemptToOrphanWorker, 1*time.Second, stopCh)
}
<-stopCh
}
2.1 gc.dependencyGraphBuilder.Run
gc.dependencyGraphBuilder.Run負責啟動啟動GraphBuilder，主要邏輯如下：
（1）調用gb.startMonitors，啟動前面1.1 gb.syncMonitors中提到的infomers；
（2）每隔1s循環調用gb.runProcessGraphChanges，做GraphBuilder的核心邏輯處理，核心處理邏輯會在下篇博客里進行分析。
// pkg/controller/garbagecollector/graph_builder.go
func (gb *GraphBuilder) Run(stopCh <-chan struct{}) {
klog.Infof("GraphBuilder running")
defer klog.Infof("GraphBuilder stopping")
// Set up the stop channel.
gb.monitorLock.Lock()
gb.stopCh = stopCh
gb.running = true
gb.monitorLock.Unlock()
// Start monitors and begin change processing until the stop channel is
// closed.
gb.startMonitors()
wait.Until(gb.runProcessGraphChanges, 1*time.Second, stopCh)
// Stop any running monitors.
gb.monitorLock.Lock()
defer gb.monitorLock.Unlock()
monitors := gb.monitors
stopped := 0
for _, monitor := range monitors {
if monitor.stopCh != nil {
stopped++
close(monitor.stopCh)
}
}
// reset monitors so that the graph builder can be safely re-run/synced.
gb.monitors = nil
klog.Infof("stopped %d of %d monitors", stopped, len(monitors))
}
3.garbageCollector.Sync
garbageCollector.Sync的主要功能是周期性的查詢集群中所有的deletableResources，調用gc.resyncMonitors來更新GraphBuilder的monitors，為新出現的資源對象初始化infomer和注冊eventHandler，然后啟動infomer，對已經移除的資源對象的monitors進行銷毀。
// pkg/controller/garbagecollector/garbagecollector.go
func (gc *GarbageCollector) Sync(discoveryClient discovery.ServerResourcesInterface, period time.Duration, stopCh <-chan struct{}) {
oldResources := make(map[schema.GroupVersionResource]struct{})
wait.Until(func() {
// Get the current resource list from discovery.
newResources := GetDeletableResources(discoveryClient)
...
if err := gc.resyncMonitors(newResources); err != nil {
utilruntime.HandleError(fmt.Errorf("failed to sync resource monitors (attempt %d): %v", attempt, err))
return false, nil
}
klog.V(4).Infof("resynced monitors")
...
3.1 gc.resyncMonitors
調用gc.dependencyGraphBuilder.syncMonitors：初始化infomer和注冊eventHandler；
調用gc.dependencyGraphBuilder.startMonitors：啟動infomer。
// pkg/controller/garbagecollector/garbagecollector.go
func (gc *GarbageCollector) resyncMonitors(deletableResources map[schema.GroupVersionResource]struct{}) error {
if err := gc.dependencyGraphBuilder.syncMonitors(deletableResources); err != nil {
return err
}
gc.dependencyGraphBuilder.startMonitors()
return nil
}
4.garbagecollector.NewDebugHandler
garbagecollector.NewDebugHandler暴露http服務，注冊 debug 接口，用於debug，用來提供由GraphBuilder構建的集群內所有對象的關聯關系。
// pkg/controller/garbagecollector/dump.go
func NewDebugHandler(controller *GarbageCollector) http.Handler {
return &debugHTTPHandler{controller: controller}
}
type debugHTTPHandler struct {
controller *GarbageCollector
}
func (h *debugHTTPHandler) ServeHTTP(w http.ResponseWriter, req *http.Request) {
if req.URL.Path != "/graph" {
http.Error(w, "", http.StatusNotFound)
return
}
var graph graph.Directed
if uidStrings := req.URL.Query()["uid"]; len(uidStrings) > 0 {
uids := []types.UID{}
for _, uidString := range uidStrings {
uids = append(uids, types.UID(uidString))
}
graph = h.controller.dependencyGraphBuilder.uidToNode.ToGonumGraphForObj(uids...)
} else {
graph = h.controller.dependencyGraphBuilder.uidToNode.ToGonumGraph()
}
data, err := dot.Marshal(graph, "full", "", " ")
if err != nil {
http.Error(w, err.Error(), http.StatusInternalServerError)
return
}
w.Header().Set("Content-Type", "text/vnd.graphviz")
w.Header().Set("X-Content-Type-Options", "nosniff")
w.Write(data)
w.WriteHeader(http.StatusOK)
}
獲取對象關聯關系圖
獲取全部的對象關聯關系圖：
curl http://{master_ip}:{kcm_port}/debug/controllers/garbagecollector/graph -o {output_file}
獲取特定uid的對象關聯關系圖：
curl http://{master_ip}:{kcm_port}/debug/controllers/garbagecollector/graph?uid={project_uid} -o {output_file}
示例：
curl http://192.168.1.10:10252/debug/controllers/garbagecollector/graph?uid=8727f640-112e-21eb-11dd-626400510df6 -o /home/test
總結
garbage collector介紹
Kubernetes garbage collector即垃圾收集器，存在於kube-controller-manger中，它負責回收kubernetes中的資源對象，監聽資源對象事件，更新對象之間的依賴關系，並根據對象的刪除策略來決定是否刪除其關聯對象。
garbage collector架構圖
garbage collector的主要組成為1個圖（對象關聯依賴關系圖）、2個處理器（GraphBuilder與GarbageCollector）、3個事件隊列（graphChanges、attemptToDelete與attemptToOrphan）。
garbage collector啟動分析
garbage collector的啟動主要是啟動了2個處理器（GraphBuilder與GarbageCollector），定義了對象關聯依賴關系圖以及3個事件隊列（graphChanges、attemptToDelete與attemptToOrphan）。
從apiserver list/watch的事件會放入到graphChanges隊列，而GraphBuilder從graphChanges隊列中取出事件進行處理，構建對象關聯依賴關系圖，並根據對象刪除策略將關聯對象放入attemptToDelete或attemptToOrphan隊列中，接着GarbageCollector會從attemptToDelete與attemptToOrphan隊列中取出事件，再從對象關聯依賴關系圖中獲取信息進行處理，最后回收刪除對象。