k8s garbage collector分析（1）-启动分析
garbage collector介绍
Kubernetes garbage collector即垃圾收集器，存在于kube-controller-manger中，它负责回收kubernetes中的资源对象，监听资源对象事件，更新对象之间的依赖关系，并根据对象的删除策略来决定是否删除其关联对象。
关于删除关联对象，细一点说就是，使用级联删除策略去删除一个owner时，会连带这个owner对象的dependent对象也一起删除掉。
关于对象的关联依赖关系，garbage collector会监听资源对象事件，根据资源对象中ownerReference 的值，来构建对象间的关联依赖关系，也即owner与dependent之间的关系。
关于owner与dependent的介绍
以创建deployment对象为例进行讲解。
创建deployment对象后，kube-controller-manager为其创建出replicaset对象，且自动将该deployment的信息设置到replicaset对象ownerReference值。如下面示例，即说明replicaset对象test-1-59d7f45ffb的owner为deployment对象test-1，deployment对象test-1的dependent为replicaset对象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对象创建后，kube-controller-manager为其创建出pod对象，这些pod对象也会将replicaset对象的信息设置到pod对象的ownerReference的值中，replicaset是pod的owner，pod是replicaset的dependent。
对象中ownerReference 的值，指定了owner与dependent之间的关系。
garbage collector架构图
garbage collector中最关键的代码就是garbagecollector.go与graph_builder.go两部分。
garbage collector的主要组成为1个图（对象关联依赖关系图）、2个处理器（GraphBuilder与GarbageCollector）、3个事件队列（graphChanges、attemptToDelete与attemptToOrphan）：
1个图
（1）uidToNode：对象关联依赖关系图，由GraphBuilder维护，维护着所有对象间的关联依赖关系。在该图里，每一个k8s对象会对应着关系图里的一个node，而每个node都会维护一个owner列表以及dependent列表。
示例：现有一个deployment A，replicaset B（owner为deployment A），pod C（owner为replicaset B），则对象关联依赖关系如下：
3个node，分别是A、B、C
A对应一个node，无owner，dependent列表里有B；
B对应一个node，owner列表里有A，dependent列表里有C；
C对应一个node，owner列表里有B，无dependent。
2个处理器
（1）GraphBuilder：负责维护所有对象的关联依赖关系图，并产生事件触发GarbageCollector执行对象回收删除操作。GraphBuilder从graphChanges事件队列中获取事件进行消费，根据资源对象中ownerReference的值，来构建、更新、删除对象间的关联依赖关系图，也即owner与dependent之间的关系图，然后再作为生产者生产事件，放入attemptToDelete或attemptToOrphan队列中，触发GarbageCollector执行，看是否需要进行关联对象的回收删除操作，而GarbageCollector进行对象的回收删除操作时会依赖于uidToNode这个关系图。
（2）GarbageCollector：负责回收删除对象。GarbageCollector作为消费者，从attemptToDelete与attemptToOrphan队列中取出事件进行处理，若一个对象被删除，且其删除策略为级联删除，则进行关联对象的回收删除。关于删除关联对象，细一点说就是，使用级联删除策略去删除一个owner时，会连带这个owner对象的dependent对象也一起删除掉。
3个事件队列
（1）graphChanges：list/watch apiserver，获取事件，由informer生产，由GraphBuilder消费；
（2）attemptToDelete：级联删除事件队列，由GraphBuilder生产，由GarbageCollector消费；
（3）attemptToOrphan：孤儿删除事件队列，由GraphBuilder生产，由GarbageCollector消费。
garbage collector相关启动参数分析
kcm组件启动参数中，与garbage collector相关的参数代码如下：
// 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.")
}
从代码中可以看到，kcm组件启动参数中有两个参数与garbage collector相关，分别是：
（1）enable-garbage-collector：是否开启garbage collector，默认值为true；
（2）concurrent-gc-syncs：garbage collector同步操作的worker数量，默认20。
garbage collector的源码分析将分成两部分进行，分别是：
（1）启动分析；
（2）核心处理逻辑分析。
本篇博客先对garbage collector进行启动分析。
garbage collector源码分析-启动分析
基于tag v1.17.4
https://github.com/kubernetes/kubernetes/releases/tag/v1.17.4
直接以startGarbageCollectorController函数作为garbage collector的源码分析入口。
startGarbageCollectorController
startGarbageCollectorController函数主要逻辑如下：
（1）根据EnableGarbageCollector变量的值来决定是否开启garbage collector，EnableGarbageCollector变量的值根据kcm组件启动参数--enable-garbage-collector配置获取，默认为true；不开启则直接返回，不会继续往下执行；
（2）初始化discoveryClient，主要用来获取集群中的所有资源对象；
（3）调用garbagecollector.GetDeletableResources，获取集群内garbage collector需要处理去删除回收的所有资源对象，支持delete, list, watch三种操作的资源对象称为 deletableResource；
（4）调用garbagecollector.NewGarbageCollector初始化garbage collector；
（5）调用garbageCollector.Run，启动garbage collector；
（6）调用garbageCollector.Sync监听集群中的deletableResources ，当出现新的deletableResources时同步到monitors中，确保监控集群中的所有资源；
（7）暴露http服务，注册 debug 接口，用于debug，用来提供由GraphBuilder构建的集群内所有对象的关联关系。
// 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
}
下面对startGarbageCollectorController函数里的部分逻辑稍微展开一下分析。
1.garbagecollector.NewGarbageCollector
NewGarbageCollector函数负责初始化garbage collector。主要逻辑如下：
（1）初始化GarbageCollector结构体；
（2）初始化GraphBuilder结构体，并赋值给GarbageCollector结构体的dependencyGraphBuilder属性。
// 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的主要作用是调用gb.controllerFor对各个deletableResources（deletableResources指支持 “delete”, “list”, “watch” 三种操作的资源对象）资源对象的infomer做初始化，并为资源的变化事件注册eventHandler（AddFunc、UpdateFunc 和 DeleteFunc），对于资源的add、update、delete event，都会push到graphChanges队列中，然后gb.processGraphChanges会从graphChanges队列中取出event进行处理（后面介绍garbage collector处理逻辑的时候会做详细分析）。
// 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主要是对资源对象的infomer做初始化，并为资源的变化事件注册eventHandler（AddFunc、UpdateFunc 和 DeleteFunc），对于资源的add、update、delete event，都会push到graphChanges队列中。
// 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负责启动garbage collector，主要逻辑如下：
（1）调用gc.dependencyGraphBuilder.Run：启动GraphBuilder；
（2）根据启动参数配置的worker数量，起相应数量的goroutine，执行gc.runAttemptToDeleteWorker与gc.runAttemptToOrphanWorker，两者属于GarbageCollector的核心处理逻辑，都是去删除需要被回收对象，具体分析会在下篇博客里进行分析。
// 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负责启动启动GraphBuilder，主要逻辑如下：
（1）调用gb.startMonitors，启动前面1.1 gb.syncMonitors中提到的infomers；
（2）每隔1s循环调用gb.runProcessGraphChanges，做GraphBuilder的核心逻辑处理，核心处理逻辑会在下篇博客里进行分析。
// 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询集群中所有的deletableResources，调用gc.resyncMonitors来更新GraphBuilder的monitors，为新出现的资源对象初始化infomer和注册eventHandler，然后启动infomer，对已经移除的资源对象的monitors进行销毁。
// 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
调用gc.dependencyGraphBuilder.syncMonitors：初始化infomer和注册eventHandler；
调用gc.dependencyGraphBuilder.startMonitors：启动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服务，注册 debug 接口，用于debug，用来提供由GraphBuilder构建的集群内所有对象的关联关系。
// 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)
}
获取对象关联关系图
获取全部的对象关联关系图：
curl http://{master_ip}:{kcm_port}/debug/controllers/garbagecollector/graph -o {output_file}
获取特定uid的对象关联关系图：
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
总结
garbage collector介绍
Kubernetes garbage collector即垃圾收集器，存在于kube-controller-manger中，它负责回收kubernetes中的资源对象，监听资源对象事件，更新对象之间的依赖关系，并根据对象的删除策略来决定是否删除其关联对象。
garbage collector架构图
garbage collector的主要组成为1个图（对象关联依赖关系图）、2个处理器（GraphBuilder与GarbageCollector）、3个事件队列（graphChanges、attemptToDelete与attemptToOrphan）。
garbage collector启动分析
garbage collector的启动主要是启动了2个处理器（GraphBuilder与GarbageCollector），定义了对象关联依赖关系图以及3个事件队列（graphChanges、attemptToDelete与attemptToOrphan）。
从apiserver list/watch的事件会放入到graphChanges队列，而GraphBuilder从graphChanges队列中取出事件进行处理，构建对象关联依赖关系图，并根据对象删除策略将关联对象放入attemptToDelete或attemptToOrphan队列中，接着GarbageCollector会从attemptToDelete与attemptToOrphan队列中取出事件，再从对象关联依赖关系图中获取信息进行处理，最后回收删除对象。