kube-proxy源码分析

kubernetes离线安装包，仅需三步

kube-proxy源码解析

ipvs相对于iptables模式具备较高的性能与稳定性, 本文讲以此模式的源码解析为主，如果想去了解iptables模式的原理，可以去参考其实现，架构上无差别。

kube-proxy主要功能是监听service和endpoint的事件，然后下放代理策略到机器上。 底层调用docker/libnetwork, 而libnetwork最终调用了netlink 与netns来实现ipvs的创建等动作

初始化配置

代码入口：cmd/kube-proxy/app/server.go Run() 函数

通过命令行参数去初始化proxyServer的配置

proxyServer, err := NewProxyServer(o)

type ProxyServer struct {
    // k8s client
    Client                 clientset.Interface
    EventClient            v1core.EventsGetter

    // ipvs 相关接口
    IptInterface           utiliptables.Interface
    IpvsInterface          utilipvs.Interface
    IpsetInterface         utilipset.Interface

    // 处理同步时的处理器
    Proxier                proxy.ProxyProvider

    // 代理模式，ipvs iptables userspace kernelspace(windows)四种
    ProxyMode              string
    // 配置同步周期
    ConfigSyncPeriod       time.Duration

    // service 与 endpoint 事件处理器
    ServiceEventHandler    config.ServiceHandler
    EndpointsEventHandler  config.EndpointsHandler
}

Proxier是主要入口，抽象了两个函数：

type ProxyProvider interface {
    // Sync immediately synchronizes the ProxyProvider's current state to iptables.
    Sync()
    // 定期执行
    SyncLoop()
}

ipvs 的interface 这个很重要：

type Interface interface {
    // 删除所有规则
    Flush() error
    // 增加一个virtual server
    AddVirtualServer(*VirtualServer) error

    UpdateVirtualServer(*VirtualServer) error
    DeleteVirtualServer(*VirtualServer) error
    GetVirtualServer(*VirtualServer) (*VirtualServer, error)
    GetVirtualServers() ([]*VirtualServer, error)

    // 给virtual server加个realserver, 如 VirtualServer就是一个clusterip realServer就是pod(或者自定义的endpoint)
    AddRealServer(*VirtualServer, *RealServer) error
    GetRealServers(*VirtualServer) ([]*RealServer, error)
    DeleteRealServer(*VirtualServer, *RealServer) error
}

我们在下文再详细看ipvs_linux是如何实现上面接口的

virtual server与realserver, 最重要的是ip:port，然后就是一些代理的模式如sessionAffinity等:

type VirtualServer struct {
    Address   net.IP
    Protocol  string
    Port      uint16
    Scheduler string
    Flags     ServiceFlags
    Timeout   uint32
}

type RealServer struct {
    Address net.IP
    Port    uint16
    Weight  int
}

创建apiserver client

client, eventClient, err := createClients(config.ClientConnection, master)

创建Proxier 这是仅仅关注ipvs模式的proxier

else if proxyMode == proxyModeIPVS {
        glog.V(0).Info("Using ipvs Proxier.")
        proxierIPVS, err := ipvs.NewProxier(
            iptInterface,
            ipvsInterface,
            ipsetInterface,
            utilsysctl.New(),
            execer,
            config.IPVS.SyncPeriod.Duration,
            config.IPVS.MinSyncPeriod.Duration,
            config.IPTables.MasqueradeAll,
            int(*config.IPTables.MasqueradeBit),
            config.ClusterCIDR,
            hostname,
            getNodeIP(client, hostname),
            recorder,
            healthzServer,
            config.IPVS.Scheduler,
        )
...
        proxier = proxierIPVS
        serviceEventHandler = proxierIPVS
        endpointsEventHandler = proxierIPVS

这个Proxier具备以下方法：

   +OnEndpointsAdd(endpoints *api.Endpoints)
   +OnEndpointsDelete(endpoints *api.Endpoints)
   +OnEndpointsSynced()
   +OnEndpointsUpdate(oldEndpoints, endpoints *api.Endpoints)
   +OnServiceAdd(service *api.Service)
   +OnServiceDelete(service *api.Service)
   +OnServiceSynced()
   +OnServiceUpdate(oldService, service *api.Service)
   +Sync()
   +SyncLoop()

所以ipvs的这个Proxier实现了我们需要的绝大部分接口

小结一下：

     +-----------> endpointHandler
     |
     +-----------> serviceHandler
     |                ^
     |                | +-------------> sync 定期同步等
     |                | |
ProxyServer---------> Proxier --------> service 事件回调
     |                  |
     |                  +-------------> endpoint事件回调
     |                                             |  触发
     +-----> ipvs interface ipvs handler     <-----+

启动proxyServer

1. 检查是不是带了clean up参数，如果带了那么清除所有规则退出
2. OOM adjuster貌似没实现，忽略
3. resouceContainer也没实现，忽略
4. 启动metrics服务器，这个挺重要，比如我们想监控时可以传入这个参数, 包含promethus的 metrics. metrics-bind-address参数
5. 启动informer, 开始监听事件，分别启动协程处理。

1 2 3 4我们都不用太关注，细看5即可：

informerFactory := informers.NewSharedInformerFactory(s.Client, s.ConfigSyncPeriod)

serviceConfig := config.NewServiceConfig(informerFactory.Core().InternalVersion().Services(), s.ConfigSyncPeriod)
// 注册 service handler并启动
serviceConfig.RegisterEventHandler(s.ServiceEventHandler)
// 这里面仅仅是把ServiceEventHandler赋值给informer回调
go serviceConfig.Run(wait.NeverStop)

endpointsConfig := config.NewEndpointsConfig(informerFactory.Core().InternalVersion().Endpoints(), s.ConfigSyncPeriod)
// 注册endpoint
endpointsConfig.RegisterEventHandler(s.EndpointsEventHandler)
go endpointsConfig.Run(wait.NeverStop)

go informerFactory.Start(wait.NeverStop)

serviceConfig.Run与endpointConfig.Run仅仅是给回调函数赋值, 所以注册的handler就给了informer, informer监听到事件时就会回调：

for i := range c.eventHandlers {
    glog.V(3).Infof("Calling handler.OnServiceSynced()")
    c.eventHandlers[i].OnServiceSynced()
}

那么问题来了，注册进去的这个handler是啥？ 回顾一下上文的

        serviceEventHandler = proxierIPVS
        endpointsEventHandler = proxierIPVS

所以都是这个proxierIPVS

handler的回调函数, informer会回调这几个函数，所以我们在自己开发时实现这个interface注册进去即可：

type ServiceHandler interface {
    // OnServiceAdd is called whenever creation of new service object
    // is observed.
    OnServiceAdd(service *api.Service)
    // OnServiceUpdate is called whenever modification of an existing
    // service object is observed.
    OnServiceUpdate(oldService, service *api.Service)
    // OnServiceDelete is called whenever deletion of an existing service
    // object is observed.
    OnServiceDelete(service *api.Service)
    // OnServiceSynced is called once all the initial even handlers were
    // called and the state is fully propagated to local cache.
    OnServiceSynced()
}

开始监听

go informerFactory.Start(wait.NeverStop)

这里执行后，我们创建删除service endpoint等动作都会被监听到，然后回调,回顾一下上面的图，最终都是由Proxier去实现，所以后面我们重点关注Proxier即可

s.Proxier.SyncLoop()

然后开始SyncLoop,下文开讲

Proxier 实现

我们创建一个service时OnServiceAdd方法会被调用, 这里记录一下之前的状态与当前状态两个东西，然后发个信号给syncRunner让它去处理：

func (proxier *Proxier) OnServiceAdd(service *api.Service) {
    namespacedName := types.NamespacedName{Namespace: service.Namespace, Name: service.Name}
    if proxier.serviceChanges.update(&namespacedName, nil, service) && proxier.isInitialized() {
        proxier.syncRunner.Run()
    }
}

记录service 信息,可以看到没做什么事，就是把service存在map里, 如果没变直接删掉map信息不做任何处理：

change, exists := scm.items[*namespacedName]
if !exists {
    change = &serviceChange{}
    // 老的service信息
    change.previous = serviceToServiceMap(previous)
    scm.items[*namespacedName] = change
}
// 当前监听到的service信息
change.current = serviceToServiceMap(current)

如果一样，直接删除
if reflect.DeepEqual(change.previous, change.current) {
    delete(scm.items, *namespacedName)
}

proxier.syncRunner.Run() 里面就发送了一个信号

select {
case bfr.run <- struct{}{}:
default:
}

这里面处理了这个信号

s.Proxier.SyncLoop()

func (proxier *Proxier) SyncLoop() {
    // Update healthz timestamp at beginning in case Sync() never succeeds.
    if proxier.healthzServer != nil {
        proxier.healthzServer.UpdateTimestamp()
    }
    proxier.syncRunner.Loop(wait.NeverStop)
}

runner里收到信号执行，没收到信号会定期执行：

func (bfr *BoundedFrequencyRunner) Loop(stop <-chan struct{}) {
    glog.V(3).Infof("%s Loop running", bfr.name)
    bfr.timer.Reset(bfr.maxInterval)
    for {
        select {
        case <-stop:
            bfr.stop()
            glog.V(3).Infof("%s Loop stopping", bfr.name)
            return
        case <-bfr.timer.C():  // 定期执行
            bfr.tryRun()
        case <-bfr.run:
            bfr.tryRun()       // 收到事件信号执行
        }
    }
}

这个bfr runner里我们最需要主意的是一个回调函数，tryRun里检查这个回调是否满足被调度的条件：

type BoundedFrequencyRunner struct {
    name        string        // the name of this instance
    minInterval time.Duration // the min time between runs, modulo bursts
    maxInterval time.Duration // the max time between runs

    run chan struct{} // try an async run

    mu      sync.Mutex  // guards runs of fn and all mutations
    fn      func()      // function to run, 这个回调
    lastRun time.Time   // time of last run
    timer   timer       // timer for deferred runs
    limiter rateLimiter // rate limiter for on-demand runs
}

// 传入的proxier.syncProxyRules这个函数
proxier.syncRunner = async.NewBoundedFrequencyRunner("sync-runner", proxier.syncProxyRules, minSyncPeriod, syncPeriod, burstSyncs)

这是个600行左右的搓逼函数，也是处理主要逻辑的地方。

syncProxyRules

1. 设置一些iptables规则，如mark与comment
2. 确定机器上有网卡，ipvs需要绑定地址到上面
3. 确定有ipset，ipset是iptables的扩展，可以给一批地址设置iptables规则
   
   ...(又臭又长，重复代码多，看不下去了，细节问题自己去看吧)
4. 我们最关注的，如何去处理VirtualServer的

serv := &utilipvs.VirtualServer{
    Address:   net.ParseIP(ingress.IP),
    Port:      uint16(svcInfo.port),
    Protocol:  string(svcInfo.protocol),
    Scheduler: proxier.ipvsScheduler,
}
if err := proxier.syncService(svcNameString, serv, false); err == nil {
    if err := proxier.syncEndpoint(svcName, svcInfo.onlyNodeLocalEndpoints, serv); err != nil {
    }
}

看下实现, 如果没有就创建，如果已存在就更新, 给网卡绑定service的cluster ip：

func (proxier *Proxier) syncService(svcName string, vs *utilipvs.VirtualServer, bindAddr bool) error {
    appliedVirtualServer, _ := proxier.ipvs.GetVirtualServer(vs)
    if appliedVirtualServer == nil || !appliedVirtualServer.Equal(vs) {
        if appliedVirtualServer == nil {
            if err := proxier.ipvs.AddVirtualServer(vs); err != nil {
                return err
            }
        } else {
            if err := proxier.ipvs.UpdateVirtualServer(appliedVirtualServer); err != nil {
                return err
            }
        }
    }

    // bind service address to dummy interface even if service not changed,
    // in case that service IP was removed by other processes
    if bindAddr {
        _, err := proxier.netlinkHandle.EnsureAddressBind(vs.Address.String(), DefaultDummyDevice)
        if err != nil {
            return err
        }
    }
    return nil
}

创建service实现

现在可以去看ipvs的AddVirtualServer的实现了，主要是利用socket与内核进程通信做到的。

pkg/util/ipvs/ipvs_linux.go 里 runner结构体实现了这些方法, 这里用到了 docker/libnetwork/ipvs库：

// runner implements Interface.
type runner struct {
    exec       utilexec.Interface
    ipvsHandle *ipvs.Handle
}

// New returns a new Interface which will call ipvs APIs.
func New(exec utilexec.Interface) Interface {
    ihandle, err := ipvs.New("") // github.com/docker/libnetwork/ipvs
    if err != nil {
        glog.Errorf("IPVS interface can't be initialized, error: %v", err)
        return nil
    }
    return &runner{
        exec:       exec,
        ipvsHandle: ihandle,
    }
}

New的时候创建了一个特殊的socket, 这里与我们普通的socket编程无差别，关键是syscall.AF_NETLINK这个参数，代表与内核进程通信：

sock, err := nl.GetNetlinkSocketAt(n, netns.None(), syscall.NETLINK_GENERIC)

func getNetlinkSocket(protocol int) (*NetlinkSocket, error) {
    fd, err := syscall.Socket(syscall.AF_NETLINK, syscall.SOCK_RAW|syscall.SOCK_CLOEXEC, protocol)
    if err != nil {
        return nil, err
    }
    s := &NetlinkSocket{
        fd: int32(fd),
    }
    s.lsa.Family = syscall.AF_NETLINK
    if err := syscall.Bind(fd, &s.lsa); err != nil {
        syscall.Close(fd)
        return nil, err
    }

    return s, nil
}

创建一个service, 转换成docker service格式，直接调用:

// AddVirtualServer is part of Interface.
func (runner *runner) AddVirtualServer(vs *VirtualServer) error {
    eSvc, err := toBackendService(vs)
    if err != nil {
        return err
    }
    return runner.ipvsHandle.NewService(eSvc)
}

然后就是把service信息打包，往socket里面写即可：

func (i *Handle) doCmdwithResponse(s *Service, d *Destination, cmd uint8) ([][]byte, error) {
    req := newIPVSRequest(cmd)
    req.Seq = atomic.AddUint32(&i.seq, 1)

    if s == nil {
        req.Flags |= syscall.NLM_F_DUMP                    //Flag to dump all messages
        req.AddData(nl.NewRtAttr(ipvsCmdAttrService, nil)) //Add a dummy attribute
    } else {
        req.AddData(fillService(s))
    } // 把service塞到请求中

    if d == nil {
        if cmd == ipvsCmdGetDest {
            req.Flags |= syscall.NLM_F_DUMP
        }

    } else {
        req.AddData(fillDestinaton(d))
    }

    // 给内核进程发送service信息
    res, err := execute(i.sock, req, 0)
    if err != nil {
        return [][]byte{}, err
    }

    return res, nil
}

构造请求

func newIPVSRequest(cmd uint8) *nl.NetlinkRequest {
    return newGenlRequest(ipvsFamily, cmd)
}

在构造请求时传入的是ipvs协议簇

然后构造一个与内核通信的消息头

func NewNetlinkRequest(proto, flags int) *NetlinkRequest {
    return &NetlinkRequest{
        NlMsghdr: syscall.NlMsghdr{
            Len:   uint32(syscall.SizeofNlMsghdr),
            Type:  uint16(proto),
            Flags: syscall.NLM_F_REQUEST | uint16(flags),
            Seq:   atomic.AddUint32(&nextSeqNr, 1),
        },
    }
}

给消息加Data,这个Data是个数组，需要实现两个方法：

type NetlinkRequestData interface {
    Len() int  // 长度
    Serialize() []byte // 序列化, 内核通信也需要一定的数据格式，service信息也需要实现
}

比如 header是这样序列化的, 一看愣住了，思考好久才看懂：

拆下看：

([unsafe.Sizeof(*hdr)]byte) 一个[]byte类型，长度就是结构体大小

(unsafe.Pointer(hdr))把结构体转成byte指针类型

加个*取它的值

用[:]转成byte返回

func (hdr *genlMsgHdr) Serialize() []byte {
    return (*(*[unsafe.Sizeof(*hdr)]byte)(unsafe.Pointer(hdr)))[:]
}

发送service信息给内核

一个很普通的socket发送接收数据

func execute(s *nl.NetlinkSocket, req *nl.NetlinkRequest, resType uint16) ([][]byte, error) {
    var (
        err error
    )

    if err := s.Send(req); err != nil {
        return nil, err
    }

    pid, err := s.GetPid()
    if err != nil {
        return nil, err
    }

    var res [][]byte

done:
    for {
        msgs, err := s.Receive()
        if err != nil {
            return nil, err
        }
        for _, m := range msgs {
            if m.Header.Seq != req.Seq {
                continue
            }
            if m.Header.Pid != pid {
                return nil, fmt.Errorf("Wrong pid %d, expected %d", m.Header.Pid, pid)
            }
            if m.Header.Type == syscall.NLMSG_DONE {
                break done
            }
            if m.Header.Type == syscall.NLMSG_ERROR {
                error := int32(native.Uint32(m.Data[0:4]))
                if error == 0 {
                    break done
                }
                return nil, syscall.Errno(-error)
            }
            if resType != 0 && m.Header.Type != resType {
                continue
            }
            res = append(res, m.Data)
            if m.Header.Flags&syscall.NLM_F_MULTI == 0 {
                break done
            }
        }
    }
    return res, nil
}

Service 数据打包

这里比较细，核心思想就是内核只认一定格式的标准数据，我们把service信息按其标准打包发送给内核即可。

至于怎么打包的就不详细讲了。

func fillService(s *Service) nl.NetlinkRequestData {
    cmdAttr := nl.NewRtAttr(ipvsCmdAttrService, nil)
    nl.NewRtAttrChild(cmdAttr, ipvsSvcAttrAddressFamily, nl.Uint16Attr(s.AddressFamily))
    if s.FWMark != 0 {
        nl.NewRtAttrChild(cmdAttr, ipvsSvcAttrFWMark, nl.Uint32Attr(s.FWMark))
    } else {
        nl.NewRtAttrChild(cmdAttr, ipvsSvcAttrProtocol, nl.Uint16Attr(s.Protocol))
        nl.NewRtAttrChild(cmdAttr, ipvsSvcAttrAddress, rawIPData(s.Address))

        // Port needs to be in network byte order.
        portBuf := new(bytes.Buffer)
        binary.Write(portBuf, binary.BigEndian, s.Port)
        nl.NewRtAttrChild(cmdAttr, ipvsSvcAttrPort, portBuf.Bytes())
    }

    nl.NewRtAttrChild(cmdAttr, ipvsSvcAttrSchedName, nl.ZeroTerminated(s.SchedName))
    if s.PEName != "" {
        nl.NewRtAttrChild(cmdAttr, ipvsSvcAttrPEName, nl.ZeroTerminated(s.PEName))
    }
    f := &ipvsFlags{
        flags: s.Flags,
        mask:  0xFFFFFFFF,
    }
    nl.NewRtAttrChild(cmdAttr, ipvsSvcAttrFlags, f.Serialize())
    nl.NewRtAttrChild(cmdAttr, ipvsSvcAttrTimeout, nl.Uint32Attr(s.Timeout))
    nl.NewRtAttrChild(cmdAttr, ipvsSvcAttrNetmask, nl.Uint32Attr(s.Netmask))
    return cmdAttr
}

总结

Service总体来讲代码比较简单，但是觉得有些地方实现的有点绕，不够简单直接。 总体来说就是监听apiserver事件，然后比对 处理，定期也会去执行同步策略.

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