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 = trues := SchedulerServer{KubeSchedulerConfiguration: cfg,}return &s
}

上面NewSchedulerServer中api.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"