以下代码分析基于
kubernetes v1.12.0版本。
scheduler的cmd代码目录结构如下：
kube-scheduler
├── BUILD
├── OWNERS
├── app # app的目录下主要为运行scheduler相关的对象
│ ├── BUILD
│ ├── config
│ │ ├── BUILD
│ │ └── config.go # Scheduler的配置对象config
│ ├── options # options主要记录 Scheduler 使用到的参数
│ │ ├── BUILD
│ │ ├── configfile.go
│ │ ├── deprecated.go
│ │ ├── deprecated_test.go
│ │ ├── insecure_serving.go
│ │ ├── insecure_serving_test.go
│ │ ├── options.go # 主要包括Options、NewOptions、AddFlags、Config等函数
│ │ └── options_test.go
│ └── server.go # 主要包括 NewSchedulerCommand、NewSchedulerConfig、Run等函数
└── scheduler.go # main入口函数1. Main函数
此部分的代码为/cmd/kube-scheduler/scheduler.go
kube-scheduler的入口函数Main函数，仍然是采用统一的代码风格，使用Cobra命令行框架。
func main() {
rand.Seed(time.Now().UTC().UnixNano())
command := app.NewSchedulerCommand()
// TODO: once we switch everything over to Cobra commands, we can go back to calling
// utilflag.InitFlags() (by removing its pflag.Parse() call). For now, we have to set the
// normalize func and add the go flag set by hand.
pflag.CommandLine.SetNormalizeFunc(utilflag.WordSepNormalizeFunc)
pflag.CommandLine.AddGoFlagSet(goflag.CommandLine)
// utilflag.InitFlags()
logs.InitLogs()
defer logs.FlushLogs()
if err := command.Execute(); err != nil {
fmt.Fprintf(os.Stderr, "%v\n", err)
os.Exit(1)
}
}核心代码：
// 初始化scheduler命令结构体
command := app.NewSchedulerCommand()
// 执行Execute
err := command.Execute()此部分的代码为/cmd/kube-scheduler/app/server.go
NewSchedulerCommand主要用来构造和初始化SchedulerCommand结构体，
// NewSchedulerCommand creates a *cobra.Command object with default parameters
func NewSchedulerCommand() *cobra.Command {
opts, err := options.NewOptions()
if err != nil {
glog.Fatalf("unable to initialize command options: %v", err)
}
cmd := &cobra.Command{
Use: "kube-scheduler",
Long: `The Kubernetes scheduler is a policy-rich, topology-aware,
workload-specific function that significantly impacts availability, performance,
and capacity. The scheduler needs to take into account individual and collective
resource requirements, quality of service requirements, hardware/software/policy
constraints, affinity and anti-affinity specifications, data locality, inter-workload
interference, deadlines, and so on. Workload-specific requirements will be exposed
through the API as necessary.`,
Run: func(cmd *cobra.Command, args []string) {
verflag.PrintAndExitIfRequested()
utilflag.PrintFlags(cmd.Flags())
if len(args) != 0 {
fmt.Fprint(os.Stderr, "arguments are not supported\n")
}
if errs := opts.Validate(); len(errs) > 0 {
fmt.Fprintf(os.Stderr, "%v\n", utilerrors.NewAggregate(errs))
os.Exit(1)
}
if len(opts.WriteConfigTo) > 0 {
if err := options.WriteConfigFile(opts.WriteConfigTo, &opts.ComponentConfig); err != nil {
fmt.Fprintf(os.Stderr, "%v\n", err)
os.Exit(1)
}
glog.Infof("Wrote configuration to: %s\n", opts.WriteConfigTo)
return
}
c, err := opts.Config()
if err != nil {
fmt.Fprintf(os.Stderr, "%v\n", err)
os.Exit(1)
}
stopCh := make(chan struct{})
if err := Run(c.Complete(), stopCh); err != nil {
fmt.Fprintf(os.Stderr, "%v\n", err)
os.Exit(1)
}
},
}
opts.AddFlags(cmd.Flags())
cmd.MarkFlagFilename("config", "yaml", "yml", "json")
return cmd
}核心代码：
// 构造option
opts, err := options.NewOptions()
// 初始化config对象
c, err := opts.Config()
// 执行run函数
err := Run(c.Complete(), stopCh)
// 添加参数
opts.AddFlags(cmd.Flags())NewOptions主要用来构造SchedulerServer使用的参数和上下文，其中核心参数是KubeSchedulerConfiguration。
opts, err := options.NewOptions()NewOptions:
// NewOptions returns default scheduler app options.
func NewOptions() (*Options, error) {
cfg, err := newDefaultComponentConfig()
if err != nil {
return nil, err
}
hhost, hport, err := splitHostIntPort(cfg.HealthzBindAddress)
if err != nil {
return nil, err
}
o := &Options{
ComponentConfig: *cfg,
SecureServing: nil, // TODO: enable with apiserveroptions.NewSecureServingOptions()
CombinedInsecureServing: &CombinedInsecureServingOptions{
Healthz: &apiserveroptions.DeprecatedInsecureServingOptions{
BindNetwork: "tcp",
},
Metrics: &apiserveroptions.DeprecatedInsecureServingOptions{
BindNetwork: "tcp",
},
BindPort: hport,
BindAddress: hhost,
},
Authentication: nil, // TODO: enable with apiserveroptions.NewDelegatingAuthenticationOptions()
Authorization: nil, // TODO: enable with apiserveroptions.NewDelegatingAuthorizationOptions()
Deprecated: &DeprecatedOptions{
UseLegacyPolicyConfig: false,
PolicyConfigMapNamespace: metav1.NamespaceSystem,
},
}
return o, nil
}Config初始化调度器的配置对象。
c, err := opts.Config()Config函数主要执行以下操作：
- 构建scheduler client、leaderElectionClient、eventClient。
- 创建event recorder
- 设置leader选举
- 创建informer对象，主要函数有
NewSharedInformerFactory和NewPodInformer。
Config具体代码如下：
// Config return a scheduler config object
func (o *Options) Config() (*schedulerappconfig.Config, error) {
c := &schedulerappconfig.Config{}
if err := o.ApplyTo(c); err != nil {
return nil, err
}
// prepare kube clients.
client, leaderElectionClient, eventClient, err := createClients(c.ComponentConfig.ClientConnection, o.Master, c.ComponentConfig.LeaderElection.RenewDeadline.Duration)
if err != nil {
return nil, err
}
// Prepare event clients.
eventBroadcaster := record.NewBroadcaster()
recorder := eventBroadcaster.NewRecorder(legacyscheme.Scheme, corev1.EventSource{Component: c.ComponentConfig.SchedulerName})
// Set up leader election if enabled.
var leaderElectionConfig *leaderelection.LeaderElectionConfig
if c.ComponentConfig.LeaderElection.LeaderElect {
leaderElectionConfig, err = makeLeaderElectionConfig(c.ComponentConfig.LeaderElection, leaderElectionClient, recorder)
if err != nil {
return nil, err
}
}
c.Client = client
c.InformerFactory = informers.NewSharedInformerFactory(client, 0)
c.PodInformer = factory.NewPodInformer(client, 0)
c.EventClient = eventClient
c.Recorder = recorder
c.Broadcaster = eventBroadcaster
c.LeaderElection = leaderElectionConfig
return c, nil
}AddFlags为SchedulerServer添加指定的参数。
opts.AddFlags(cmd.Flags())AddFlags函数的具体代码如下：
// AddFlags adds flags for the scheduler options.
func (o *Options) AddFlags(fs *pflag.FlagSet) {
fs.StringVar(&o.ConfigFile, "config", o.ConfigFile, "The path to the configuration file. Flags override values in this file.")
fs.StringVar(&o.WriteConfigTo, "write-config-to", o.WriteConfigTo, "If set, write the configuration values to this file and exit.")
fs.StringVar(&o.Master, "master", o.Master, "The address of the Kubernetes API server (overrides any value in kubeconfig)")
o.SecureServing.AddFlags(fs)
o.CombinedInsecureServing.AddFlags(fs)
o.Authentication.AddFlags(fs)
o.Authorization.AddFlags(fs)
o.Deprecated.AddFlags(fs, &o.ComponentConfig)
leaderelectionconfig.BindFlags(&o.ComponentConfig.LeaderElection.LeaderElectionConfiguration, fs)
utilfeature.DefaultFeatureGate.AddFlag(fs)
}3. Run
此部分的代码为/cmd/kube-scheduler/app/server.go
err := Run(c.Complete(), stopCh) Run运行一个不退出的常驻进程，来执行scheduler的相关操作。
Run函数的主要内容如下：
- 通过scheduler config来创建scheduler的结构体。
- 运行event broadcaster、healthz server、metrics server。
- 运行所有的informer并在调度前等待cache的同步（重点）。
- 执行
sched.Run()来运行scheduler的调度逻辑。 - 如果多个scheduler并开启了
LeaderElect，则执行leader选举。
以下对重点代码分开分析：
NewSchedulerConfig初始化SchedulerConfig（此部分具体逻辑待后续专门分析），最后初始化生成scheduler结构体。
// Build a scheduler config from the provided algorithm source.
schedulerConfig, err := NewSchedulerConfig(c)
if err != nil {
return err
}
// Create the scheduler.
sched := scheduler.NewFromConfig(schedulerConfig)运行PodInformer，并运行InformerFactory。此部分的逻辑为client-go的informer机制，在Informer机制中有详细分析。
// Start all informers.
go c.PodInformer.Informer().Run(stopCh)
c.InformerFactory.Start(stopCh)在调度前等待cache同步。
// Wait for all caches to sync before scheduling.
c.InformerFactory.WaitForCacheSync(stopCh)
controller.WaitForCacheSync("scheduler", stopCh, c.PodInformer.Informer().HasSynced)InformerFactory.WaitForCacheSync等待所有启动的informer的cache进行同步，保持本地的store信息与etcd的信息是最新一致的。
// WaitForCacheSync waits for all started informers' cache were synced.
func (f *sharedInformerFactory) WaitForCacheSync(stopCh <-chan struct{}) map[reflect.Type]bool {
informers := func() map[reflect.Type]cache.SharedIndexInformer {
f.lock.Lock()
defer f.lock.Unlock()
informers := map[reflect.Type]cache.SharedIndexInformer{}
for informerType, informer := range f.informers {
if f.startedInformers[informerType] {
informers[informerType] = informer
}
}
return informers
}()
res := map[reflect.Type]bool{}
for informType, informer := range informers {
res[informType] = cache.WaitForCacheSync(stopCh, informer.HasSynced)
}
return res
}接着调用 cache.WaitForCacheSync。
// WaitForCacheSync waits for caches to populate. It returns true if it was successful, false
// if the controller should shutdown
func WaitForCacheSync(stopCh <-chan struct{}, cacheSyncs ...InformerSynced) bool {
err := wait.PollUntil(syncedPollPeriod,
func() (bool, error) {
for _, syncFunc := range cacheSyncs {
if !syncFunc() {
return false, nil
}
}
return true, nil
},
stopCh)
if err != nil {
glog.V(2).Infof("stop requested")
return false
}
glog.V(4).Infof("caches populated")
return true
}controller.WaitForCacheSync是对cache.WaitForCacheSync的一层封装，通过不同的controller的名字来记录不同controller等待cache同步。
controller.WaitForCacheSync("scheduler", stop, s.PodInformer.Informer().HasSynced)controller.WaitForCacheSync具体代码如下：
// WaitForCacheSync is a wrapper around cache.WaitForCacheSync that generates log messages
// indicating that the controller identified by controllerName is waiting for syncs, followed by
// either a successful or failed sync.
func WaitForCacheSync(controllerName string, stopCh <-chan struct{}, cacheSyncs ...cache.InformerSynced) bool {
glog.Infof("Waiting for caches to sync for %s controller", controllerName)
if !cache.WaitForCacheSync(stopCh, cacheSyncs...) {
utilruntime.HandleError(fmt.Errorf("Unable to sync caches for %s controller", controllerName))
return false
}
glog.Infof("Caches are synced for %s controller", controllerName)
return true
}如果有多个scheduler，并开启leader选举，则运行LeaderElector直到选举结束或退出。
// If leader election is enabled, run via LeaderElector until done and exit.
if c.LeaderElection != nil {
c.LeaderElection.Callbacks = leaderelection.LeaderCallbacks{
OnStartedLeading: run,
OnStoppedLeading: func() {
utilruntime.HandleError(fmt.Errorf("lost master"))
},
}
leaderElector, err := leaderelection.NewLeaderElector(*c.LeaderElection)
if err != nil {
return fmt.Errorf("couldn't create leader elector: %v", err)
}
leaderElector.Run(ctx)
return fmt.Errorf("lost lease")
}// Prepare a reusable run function.
run := func(ctx context.Context) {
sched.Run()
<-ctx.Done()
}
ctx, cancel := context.WithCancel(context.TODO()) // TODO once Run() accepts a context, it should be used here
defer cancel()
go func() {
select {
case <-stopCh:
cancel()
case <-ctx.Done():
}
}()
...
run(ctx)Scheduler.Run先等待cache同步，然后开启调度逻辑的goroutine。
Scheduler.Run的具体代码如下：
// Run begins watching and scheduling. It waits for cache to be synced, then starts a goroutine and returns immediately.
func (sched *Scheduler) Run() {
if !sched.config.WaitForCacheSync() {
return
}
go wait.Until(sched.scheduleOne, 0, sched.config.StopEverything)
}以上是对/cmd/kube-scheduler/scheduler.go部分代码的分析，Scheduler.Run后续的具体代码位于pkg/scheduler/scheduler.go待后续文章分析。
参考：