kubernetes之kube-scheduler模块

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对于kubernetes的使用者来看，kube-scheduler模块到底是什么？

　　kube-scheduler是 Kubernetes 集群的默认调度器，并且是集群 控制面 的一部分。对每一个新创建的 Pod 或者是未被调度的 Pod，kube-scheduler 会过滤所有的node，然后选择一个最优的 Node 去运行这个 Pod。

首先，我们看一下kubernetes集群架构与组件图。

 

 

 根据上图，对于scheduler模块。在看源码前想到了这么几个问题？

1.scheduler获取消息数据格式、输出数据格式？
2.社区有人说增加缓存能有效提高scheduler的效率，是否是真的？

从代码中获取问题结果：

scheduler代码

首先cmd入口，schduler.go：

package main

import (
	"math/rand"
	"os"
	"time"

	"github.com/spf13/pflag"

	cliflag "k8s.io/component-base/cli/flag"
	"k8s.io/component-base/logs"
	_ "k8s.io/component-base/metrics/prometheus/clientgo"
	"k8s.io/kubernetes/cmd/kube-schedulkeyr/app"
)

func main() {
	rand.Seed(time.Now().UnixNano())
　　
　　　　　//获取一个NewSchedulerCommand结构体
　　　　　command := app.NewSchedulerCommand()

	pflag.CommandLine.SetNormalizeFunc(cliflag.WordSepNormalizeFunc)
	// utilflag.InitFlags()
	logs.InitLogs()
	defer logs.FlushLogs()

	if err := command.Execute(); err != nil {
		os.Exit(1)
	}
}

　第二层入口：

　　command := app.NewSchedulerCommand()然而，app从这里引入："k8s.io/kubernetes/cmd/kube-schedulkeyr/app"

可以追溯到文件app目录下的server.go:

函数：NewSchedulerCommand

// NewSchedulerCommand creates a *cobra.Command object with default parameters and registryOptions
//cobra是一个命令行启动框架.这里不做详细解释，了解更多可以看这个：https://github.com/spf13/cobra。
func NewSchedulerCommand(registryOptions ...Option) *cobra.Command {
	opts, err := options.NewOptions()
	if err != nil {
		klog.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. See [scheduling](https://kubernetes.io/docs/concepts/scheduling/)
for more information about scheduling and the kube-scheduler component.`,
		Run: func(cmd *cobra.Command, args []string) {
			if err := runCommand(cmd, args, opts, registryOptions...); err != nil {
				fmt.Fprintf(os.Stderr, "%v\n", err)
				os.Exit(1)
			}
		},
	}
	fs := cmd.Flags()
	namedFlagSets := opts.Flags()
	verflag.AddFlags(namedFlagSets.FlagSet("global"))
	globalflag.AddGlobalFlags(namedFlagSets.FlagSet("global"), cmd.Name())
	for _, f := range namedFlagSets.FlagSets {
		fs.AddFlagSet(f)
	}

	usageFmt := "Usage:\n  %s\n"
	cols, _, _ := term.TerminalSize(cmd.OutOrStdout())
	cmd.SetUsageFunc(func(cmd *cobra.Command) error {
		fmt.Fprintf(cmd.OutOrStderr(), usageFmt, cmd.UseLine())
		cliflag.PrintSections(cmd.OutOrStderr(), namedFlagSets, cols)
		return nil
	})
	cmd.SetHelpFunc(func(cmd *cobra.Command, args []string) {
		fmt.Fprintf(cmd.OutOrStdout(), "%s\n\n"+usageFmt, cmd.Long, cmd.UseLine())
		cliflag.PrintSections(cmd.OutOrStdout(), namedFlagSets, cols)
	})
	cmd.MarkFlagFilename("config", "yaml", "yml", "json")

	return cmd
}