从源码解析kube-scheduler默认的配置

本文作为Kubernetes Scheduler源码分析的番外篇,补充一个方面的分析:从源码层面解析kube-scheduler的默认配置是怎么做的。

从头来看,在kube-scheduler的main函数中,s := options.NewSchedulerServer()创建SchedulerServer时,是按照默认参数创建的。

--- plugin/cmd/kube-scheduler/scheduler.go:30 ---

func main() {
    s := options.NewSchedulerServer()
    s.AddFlags(pflag.CommandLine)

    flag.InitFlags()
    logs.InitLogs()
    defer logs.FlushLogs()

    verflag.PrintAndExitIfRequested()

    if err := app.Run(s); err != nil {
        glog.Fatalf("scheduler app failed to run: %v", err)
    }
}

--- plugin/cmd/kube-scheduler/app/options/options.go:44 ---

// NewSchedulerServer creates a new SchedulerServer with default parameters
func NewSchedulerServer() *SchedulerServer {
    versioned := &v1alpha1.KubeSchedulerConfiguration{}
    api.Scheme.Default(versioned)
    cfg := componentconfig.KubeSchedulerConfiguration{}
    api.Scheme.Convert(versioned, &cfg, nil)
    cfg.LeaderElection.LeaderElect = true
    s := SchedulerServer{
        KubeSchedulerConfiguration: cfg,
    }
    return &s
}

上面NewSchedulerServerapi.Scheme.Default(versioned)就是设置默认参数的操作。看看Default(…)的代码:

--- pkg/runtime/scheme.go:439 ---

// Default sets defaults on the provided Object.
func (s *Scheme) Default(src Object) {
    if fn, ok := s.defaulterFuncs[reflect.TypeOf(src)]; ok {
        fn(src)
    }
}

原来Default(…)做的工作就是从Scheme.defaulterFuncs这个Map中获取&v1alpha1.KubeSchedulerConfiguration{}这个type对应的defaultFunc fn,并执行fn(&v1alpha1.KubeSchedulerConfiguration{})来完成默认参数的配置。

OK,那么问题来了。这些type对应的defaultFunc是怎么register到Scheme.defaulterFuncs这个Map中的呢?

答案就在pkg/apis/componentconfig/v1alpha1/register.go中定义的全局变量SchemeBuilder。SchemeBuilder = runtime.NewSchemeBuilder(addKnownTypes, addDefaultingFuncs)在创建SchemeBuilder时就调用了addDefaultFuncs函数。注册defaultFunc的工作应该就是在addDefaultingFuncs方法中实现的。

看看addDefaultingFuncs的实现,果不其然啊.SetDefaults_KubeSchedulerConfiguration就是&v1alpha1.KubeSchedulerConfiguration{}对应的defaultFuncs。

---- pkg/apis/componentconfig/v1alpha1/register.go ----

var (
    SchemeBuilder = runtime.NewSchemeBuilder(addKnownTypes, addDefaultingFuncs)
    AddToScheme   = SchemeBuilder.AddToScheme
)


---- pkg/apis/componentconfig/v1alpha1/defaults.go -----

func addDefaultingFuncs(scheme *kruntime.Scheme) error {
    RegisterDefaults(scheme)
    return scheme.AddDefaultingFuncs(
        SetDefaults_KubeProxyConfiguration,
        SetDefaults_KubeSchedulerConfiguration,
        SetDefaults_LeaderElectionConfiguration,
        SetDefaults_KubeletConfiguration,
    )
}

func SetDefaults_KubeSchedulerConfiguration(obj *KubeSchedulerConfiguration) {
    if obj.Port == 0 {
        obj.Port = ports.SchedulerPort
    }
    if obj.Address == "" {
        obj.Address = "0.0.0.0"
    }
    if obj.AlgorithmProvider == "" {
        obj.AlgorithmProvider = "DefaultProvider"
    }
    if obj.ContentType == "" {
        obj.ContentType = "application/vnd.kubernetes.protobuf"
    }
    if obj.KubeAPIQPS == 0 {
        obj.KubeAPIQPS = 50.0
    }
    if obj.KubeAPIBurst == 0 {
        obj.KubeAPIBurst = 100
    }
    if obj.SchedulerName == "" {
        obj.SchedulerName = api.DefaultSchedulerName
    }
    if obj.HardPodAffinitySymmetricWeight == 0 {
        obj.HardPodAffinitySymmetricWeight = api.DefaultHardPodAffinitySymmetricWeight
    }
    if obj.FailureDomains == "" {
        obj.FailureDomains = api.DefaultFailureDomains
    }
}

再结合plugin/cmd/kube-scheduler/app/options/options.go:57定义的AddFlags,可得kube-scheduler的默认配置如下:

  • port = 10251
  • address = “0.0.0.0”
  • algorithm-provider = “DefaultProvider”
  • content-type = “application/vnd.kubernetes.protobuf”
  • kube-api-qps = 50
  • kube-api-burst = 100
  • scheduler-name = “default-scheduler”
  • hard-pod-affinity-symmetric-weight = 1
  • failure-domains = “kubernetes.io/hostname,failure-domain.beta.kubernetes.io/zone,failure-domain.beta.kubernetes.io/region”
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