k8s优雅关闭

k8s如何保障服务健壮性 之 实现优雅关闭

必要性

  1. 没有graceful的关闭将导致请求连接异常;
  2. 数据统计短时间内出现大量错误;

实现

两类信号

SIGTERM:通知进程进行graceful信号;

SIGKILL:硬终止信息;

k8s中关闭pod时的流程

https://kubernetes.io/docs/concepts/workloads/pods/pod/#termination-of-pods

简而言之就是:

  1. 先把pod标记为Terminating,此时service就会把该pod去除了;
  2. 发送SIGTERM给pod内的所有容器;
  3. pod等待grace period结束或者pod提前处理完SIGTERM;
  4. pod发送SIGKILL给所有容器;

确保信号正确传递到进程

CMD的坑

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CMD myapp

相当于:

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/bin/sh -c myapp

以上的写法,容器接收到信号的进程是/bin/sh而不是myapp,这种写法会依赖于真正使用的shell,有些shell是不会传递信号给子进程的。比如基础镜像使用的是Alpine Linux下的基础shell就不会,但是bash就可以。

使用EXEC的方式

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CMD ["myapp"]

上面的方式将会直接执行myapp,但是这种就不能把环境变量当做参数传递了???

base方式

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CMD ["/bin/bash", "-c", "myapp --arg=$ENV_VAR"]

解决以上问题。

k8s支持的几种方式

1、yaml中修改

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terminationGracePeriodSeconds: 60

2、delete命令

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kubectl delete pod-name --grace-peroid=60

3、preStop Hook

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lifecycle:
preStop:
exec:
# SIGTERM triggers a quick exit; gracefully terminate instead
command: ["/usr/sbin/nginx","-s","quit"]

4、validating webhook

指到资源清理完成才返回true,否则返回false,这样pod就能保证清理完才推出,而不会因为grace peroid被强制清除。

程序支持(最重要)

思路

  1. 首先关闭所有的监听,如果有使用服务注册之类的话,应该也把该服务从注册中去除;
  2. 然后关闭所有的空闲连接;
  3. 然后无限期等待连接处理完毕转为空闲,并关闭;
  4. 如果提供了带有超时的Context,将在服务关闭前返回Context的超时错误;

http

go http的server.Shutdown

如果你的服务是被其他服务调用的,那么关闭会比较复杂,

  1. 约定调用者的keep-alive timeout 时间,默认为30秒
  2. 服务关闭时,先设置 keep-alive 为 false
  3. 服务关闭时,再等待30秒
  4. 再调用server.Shutdown

grpc

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package main

import (
"context"
"flag"
"fmt"
"log"
"net"
"net/http"
_ "net/http/pprof"
"os"
"os/signal"
"syscall"
"time"

"github.com/blademainer/commons/pkg/logger"

"golang.org/x/sync/errgroup"
"google.golang.org/grpc"
pb "google.golang.org/grpc/examples/helloworld/helloworld"
"google.golang.org/grpc/health"
healthpb "google.golang.org/grpc/health/grpc_health_v1"
"google.golang.org/grpc/keepalive"
)

const serviceName = "myserviced"

var (
version = "no version"

debugPort = flag.Int("debugPort", 16161, "debug port")
httpPort = flag.Int("httpPort", 8888, "http port")
grpcPort = flag.Int("grpcPort", 9200, "grpc port")
healthPort = flag.Int("healthPort", 6666, "grpc health port")
)

type server struct {
}

func (s *server) SayHello(ctx context.Context, in *pb.HelloRequest) (*pb.HelloReply, error) {
log.Printf("Received: %v", in.GetName())
return &pb.HelloReply{Message: "Hello " + in.GetName()}, nil
}

func main() {
flag.Parse()

logger.Infof("Starting app, version: %v", version)

// shutdown functions
shutdownFunctions := make([]func(), 0)

ctx, cancel := context.WithCancel(context.Background())
shutdownFunctions = append(shutdownFunctions, cancel)
defer cancel()

interrupt := make(chan os.Signal, 1)
signal.Notify(interrupt, os.Interrupt, syscall.SIGTERM)
defer signal.Stop(interrupt)

g, ctx := errgroup.WithContext(ctx)

g.Go(func() error {
//profiles := pprof.Profiles()

httpServer := &http.Server{
Addr: fmt.Sprintf(":%d", *debugPort),
ReadTimeout: 10 * time.Second,
WriteTimeout: 10 * time.Second,
Handler: nil,
}
shutdownFunctions = append(shutdownFunctions, func() {
err := httpServer.Shutdown(ctx)
if err != nil {
logger.Errorf("failed to shutdown pprof server! error: %v", err.Error())
}
})

logger.Infof("pprof server serving at :%d", *debugPort)

if err := httpServer.ListenAndServe(); err != nil && err != http.ErrServerClosed {
logger.Errorf("failed to listen: %v", err.Error())
return err
}
return nil
})

// web server metrics
g.Go(func() error {
httpServer := &http.Server{
Addr: fmt.Sprintf(":%d", *httpPort),
ReadTimeout: 10 * time.Second,
WriteTimeout: 10 * time.Second,
}
shutdownFunctions = append(shutdownFunctions, func() {
err := httpServer.Shutdown(ctx)
if err != nil {
logger.Errorf("failed to shutdown pprof server! error: %v", err.Error())
}
})
logger.Infof("HTTP Metrics server serving at :%d", *httpPort)

if err := httpServer.ListenAndServe(); err != http.ErrServerClosed {
return err
}

return nil
})

// gRPC Health Server
healthServer := health.NewServer()
g.Go(func() error {
grpcHealthServer := grpc.NewServer()

shutdownFunctions = append(shutdownFunctions, func() {
healthServer.SetServingStatus(fmt.Sprintf("grpc.health.v1.%s", serviceName), healthpb.HealthCheckResponse_NOT_SERVING)
grpcHealthServer.GracefulStop()
})

healthpb.RegisterHealthServer(grpcHealthServer, healthServer)

haddr := fmt.Sprintf(":%d", *healthPort)
hln, err := net.Listen("tcp", haddr)
if err != nil {
logger.Errorf("gRPC Health server: failed to listen, error: %v", err)
os.Exit(2)
}
logger.Infof("gRPC health server serving at %s", haddr)
return grpcHealthServer.Serve(hln)
})

// gRPC server
g.Go(func() error {
addr := fmt.Sprintf(":%d", *grpcPort)
ln, err := net.Listen("tcp", addr)
if err != nil {
logger.Errorf("gRPC server: failed to listen, error: %v", err)
os.Exit(2)
}

server := &server{
}
grpcServer := grpc.NewServer(
// MaxConnectionAge is just to avoid long connection, to facilitate load balancing
// MaxConnectionAgeGrace will torn them, default to infinity
grpc.KeepaliveParams(keepalive.ServerParameters{MaxConnectionAge: 2 * time.Minute}),
)
pb.RegisterGreeterServer(grpcServer, server)
shutdownFunctions = append(shutdownFunctions, func() {
healthServer.SetServingStatus(fmt.Sprintf("grpc.health.v1.%s", serviceName), healthpb.HealthCheckResponse_NOT_SERVING)
grpcServer.GracefulStop()
})

logger.Infof("gRPC server serving at %s", addr)

healthServer.SetServingStatus(fmt.Sprintf("grpc.health.v1.%s", serviceName), healthpb.HealthCheckResponse_SERVING)

return grpcServer.Serve(ln)
})

select {
case <-interrupt:
break
case <-ctx.Done():
break
}

logger.Warnf("received shutdown signal")

for _, shutdown := range shutdownFunctions {
shutdown()
}

err := g.Wait()
if err != nil {
logger.Errorf("server returning an error, error: %v", err)
os.Exit(2)
}
}

tcp

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cmdAddr, _ := net.ResolveTCPAddr("tcp", n.cfg.Addr)
lcmd, err := net.ListenTCP("tcp", cmdAddr)
if err != nil {
log.Fatalln(err)
}
defer lcmd.Close()
quitChan := make(chan os.Signal, 1)
signal.Notify(quitChan, os.Interrupt, os.Kill, syscall.SIGTERM)
wg := sync.WaitGroup{}
for {
select {
case <-quitChan:
lcmd.Close()
wg.Wait()
return
default:
}
lcmd.SetDeadline(time.Now().Add(1e9))
conn, err := lcmd.AcceptTCP()
if opErr, ok := err.(*net.OpError); ok && opErr.Timeout() {
continue
}
if err != nil {
log.WithError(err).Errorln("Listener accept")
continue
}
wg.Add(1)
go func(){
wg.Done()
n.handleRequest(conn)
}
}