flannel 实战与源码分析（三）

来源：互联网发布：arp 添加网关mac 编辑：程序博客网时间：2024/05/21 11:29

之前一直介绍flannel的使用，现在正是进入代码讲解，看看flannel是如何实现的，先看启动

func main() {    flag.Set("logtostderr", "true")    // 解析参数    flag.Parse()    if flag.NArg() > 0 || opts.help {        fmt.Fprintf(os.Stderr, "Usage: %s [OPTION]...\n", os.Args[0])        flag.PrintDefaults()        os.Exit(0)    }    if opts.version {        fmt.Fprintln(os.Stderr, version.Version)        os.Exit(0)    }    flagutil.SetFlagsFromEnv(flag.CommandLine, "FLANNELD")    // 确定使用的端口    extIface, err := LookupExtIface(opts.iface)    if err != nil {        log.Error("Failed to find interface to use: ", err)        os.Exit(1)    }    sm, err := newSubnetManager()    if err != nil {        log.Error("Failed to create SubnetManager: ", err)        os.Exit(1)    }    // 注册 SIGINT and SIGTERM信号监听    log.Info("Installing signal handlers")    sigs := make(chan os.Signal, 1)    signal.Notify(sigs, os.Interrupt, syscall.SIGTERM)    ctx, cancel := context.WithCancel(context.Background())    go shutdown(sigs, cancel)    // 获取网络配置如backend等    config, err := getConfig(ctx, sm)    if err == errCanceled {        exit()    }    // 创建backend manager     bm := backend.NewManager(ctx, sm, extIface)    be, err := bm.GetBackend(config.BackendType)    if err != nil {        log.Errorf("Error fetching backend: %s", err)        exit()    }    bn, err := be.RegisterNetwork(ctx, config)    if err != nil {        log.Errorf("Error registering network: %s", err)        exit()    }    // 启动ipmasq    if opts.ipMasq {        err = network.SetupIPMasq(config.Network)        if err != nil {            log.Errorf("Failed to set up IP Masquerade: %v", err)        }        defer func() {            if err := network.TeardownIPMasq(config.Network); err != nil {                log.Errorf("Failed to tear down IP Masquerade: %v", err)            }        }()    }    if err := WriteSubnetFile(opts.subnetFile, config.Network, opts.ipMasq, bn); err != nil {        log.Warningf("Failed to write subnet file: %s", err)    } else {        log.Infof("Wrote subnet file to %s", opts.subnetFile)    }    // 启动 backend network阻塞直到服务启动    go bn.Run(ctx)    log.Infof("Finished starting backend.")    daemon.SdNotify(false, "READY=1")    // 重新租约    _ = MonitorLease(ctx, sm, bn)    exit()}

上面的代码是服务的入口，先解析参数，在之前的应用的时候就有使用参数

flag.StringVar(&opts.etcdEndpoints, "etcd-endpoints", "http://127.0.0.1:4001,http://127.0.0.1:2379", "a comma-delimited list of etcd endpoints")flag.StringVar(&opts.etcdPrefix, "etcd-prefix", "/coreos.com/network", "etcd prefix")flag.StringVar(&opts.iface, "iface", "", "interface to use (IP or name) for inter-host communication")flag.StringVar(&opts.subnetFile, "subnet-file", "/run/flannel/subnet.env", "filename where env variables (subnet, MTU, ... ) will be written to")flag.IntVar(&opts.subnetLeaseRenewMargin, "subnet-lease-renew-margin", 60, "Subnet lease renewal margin, in minutes.")flag.BoolVar(&opts.ipMasq, "ip-masq", false, "setup IP masquerade rule for traffic destined outside of overlay network")

这些截取的参数有事比较重要，大概说一下
etcd-endpoints：连接etcd地址
etcd-prefix ：在etcd里面路径前缀
iface：主机间流量互通的网卡
subnet-file：生成docker网络信息的路径
subnet-lease-renew-margin：这个是自网段的租约时间
ip-masq：是否启动ipmasq，就是SANT
当解析完参数后LookupExtIface检查网卡是否存在，并且返回外部接口信息

&backend.ExternalInterface{        Iface:     iface,        IfaceAddr: ifaceAddr,        ExtAddr:   extAddr,    }

Iface是制定的外网端口，如果publicip没有制定，IfaceAddr等于ExtAddr。这个容器出去的外部端口就设定成功了。
然后通过newSubnetManager去创建子网管理器，如果没有设置kubernetes子网管理的话，默认使用的就是通过etcd做子网管理，

func newSubnetManager() (subnet.Manager, error) {    if opts.kubeSubnetMgr {        return kube.NewSubnetManager()    }    cfg := &etcdv2.EtcdConfig{        Endpoints: strings.Split(opts.etcdEndpoints, ","),        Keyfile:   opts.etcdKeyfile,        Certfile:  opts.etcdCertfile,        CAFile:    opts.etcdCAFile,        Prefix:    opts.etcdPrefix,        Username:  opts.etcdUsername,        Password:  opts.etcdPassword,    }    return etcdv2.NewLocalManager(cfg)}

连接上etcd。创建网sm以后，注册SIGINT and SIGTERM这个主要是优雅的停止服务使用。getConfig里面调用的是getNetworkConfig

func (esr *etcdSubnetRegistry) getNetworkConfig(ctx context.Context) (string, error) {    key := path.Join(esr.etcdCfg.Prefix, "config")    resp, err := esr.client().Get(ctx, key, &etcd.GetOptions{Quorum: true})    if err != nil {        return "", err    }    return resp.Node.Value, nil}

这个也是就是第一篇的实战的时候设置的config。从config里面获取backend是udp还是vxlan或者是别的。通过be, err := bm.GetBackend(config.BackendType)创建相应的backend。

    befunc, ok := constructors[betype]    if !ok {        return nil, fmt.Errorf("unknown backend type: %v", betype)    }    be, err := befunc(bm.sm, bm.extIface)

这样就获取到制定的backend，下面就是开始注册网络RegisterNetwork了，
每个backend都有自己的RegisterNetwork
这里写图片描述
下面以vxlan为例

func (be *VXLANBackend) RegisterNetwork(ctx context.Context, config *subnet.Config) (backend.Network, error) {    // Parse our configuration    cfg := struct {        VNI  int        Port int        GBP  bool    }{        VNI: defaultVNI,    }    if len(config.Backend) > 0 {        if err := json.Unmarshal(config.Backend, &cfg); err != nil {            return nil, fmt.Errorf("error decoding VXLAN backend config: %v", err)        }    }    devAttrs := vxlanDeviceAttrs{        vni:       uint32(cfg.VNI),        name:      fmt.Sprintf("flannel.%v", cfg.VNI),        vtepIndex: be.extIface.Iface.Index,        vtepAddr:  be.extIface.IfaceAddr,        vtepPort:  cfg.Port,        gbp:       cfg.GBP,    }    dev, err := newVXLANDevice(&devAttrs)    if err != nil {        return nil, err    }    subnetAttrs, err := newSubnetAttrs(be.extIface.ExtAddr, dev.MACAddr())    if err != nil {        return nil, err    }    lease, err := be.subnetMgr.AcquireLease(ctx, subnetAttrs)    switch err {    case nil:    case context.Canceled, context.DeadlineExceeded:        return nil, err    default:        return nil, fmt.Errorf("failed to acquire lease: %v", err)    }    // vxlan's subnet is that of the whole overlay network (e.g. /16)    // and not that of the individual host (e.g. /24)    vxlanNet := ip.IP4Net{        IP:        lease.Subnet.IP,        PrefixLen: config.Network.PrefixLen,    }    if err = dev.Configure(vxlanNet); err != nil {        return nil, err    }    return newNetwork(be.subnetMgr, be.extIface, dev, vxlanNet, lease)}

配置vxlan的vtep设备，AcquireLease分配人一个子网租约，就是分配一个网段。再回到main里面，如果设置ipmaq就是添加一个NAT的IPtable是规则，接着就是就是写docker的网络配置文件WriteSubnetFile，最后启动go bn.Run(ctx)，它会阻塞，在另一个协程中运行，MonitorLease就是默认每隔60分钟续约一下。main解析完成，服务启动。

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