kubeadm源码分析

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sealyun
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    k8s离线安装包 三步安装，简单到难以置信

    kubeadm源码分析

    说句实在话，kubeadm的代码写的真心一般，质量不是很高。

    几个关键点来先说一下kubeadm干的几个核心的事：

    • kubeadm 生成证书在/etc/kubernetes/pki目录下
    • kubeadm 生成static pod yaml配置，全部在/etc/kubernetes/manifasts下
    • kubeadm 生成kubelet配置，kubectl配置等 在/etc/kubernetes下
    • kubeadm 通过client go去启动dns

    <!--more-->

    kubeadm init

    代码入口 cmd/kubeadm/app/cmd/init.go 建议大家去看看cobra

    找到Run函数来分析下主要流程：

    1. 如果证书不存在，就创建证书，所以如果我们有自己的证书可以把它放在/etc/kubernetes/pki下即可, 下文细看如果生成证书
        if res, _ := certsphase.UsingExternalCA(i.cfg); !res {
        if err := certsphase.CreatePKIAssets(i.cfg); err != nil {
            return err
        }
    1. 创建kubeconfig文件
            if err := kubeconfigphase.CreateInitKubeConfigFiles(kubeConfigDir, i.cfg); err != nil {
            return err
        }
    1. 创建manifest文件，etcd apiserver manager scheduler都在这里创建, 可以看到如果你的配置文件里已经写了etcd的地址了，就不创建了，这我们就可以自己装etcd集群，而不用默认单点的etcd，很有用
    controlplanephase.CreateInitStaticPodManifestFiles(manifestDir, i.cfg); 
if len(i.cfg.Etcd.Endpoints) == 0 {
    if err := etcdphase.CreateLocalEtcdStaticPodManifestFile(manifestDir, i.cfg); err != nil {
        return fmt.Errorf("error creating local etcd static pod manifest file: %v", err)
    }
}
    1. 等待APIserver和kubelet启动成功，这里就会遇到我们经常遇到的镜像拉不下来的错误，其实有时kubelet因为别的原因也会报这个错，让人误以为是镜像弄不下来
    if err := waitForAPIAndKubelet(waiter); err != nil {
    ctx := map[string]string{
        "Error":                  fmt.Sprintf("%v", err),
        "APIServerImage":         images.GetCoreImage(kubeadmconstants.KubeAPIServer, i.cfg.GetControlPlaneImageRepository(), i.cfg.KubernetesVersion, i.cfg.UnifiedControlPlaneImage),
        "ControllerManagerImage": images.GetCoreImage(kubeadmconstants.KubeControllerManager, i.cfg.GetControlPlaneImageRepository(), i.cfg.KubernetesVersion, i.cfg.UnifiedControlPlaneImage),
        "SchedulerImage":         images.GetCoreImage(kubeadmconstants.KubeScheduler, i.cfg.GetControlPlaneImageRepository(), i.cfg.KubernetesVersion, i.cfg.UnifiedControlPlaneImage),
    }

    kubeletFailTempl.Execute(out, ctx)

    return fmt.Errorf("couldn't initialize a Kubernetes cluster")
}
    1. 给master加标签，加污点, 所以想要pod调度到master上可以把污点清除了
    if err := markmasterphase.MarkMaster(client, i.cfg.NodeName); err != nil {
    return fmt.Errorf("error marking master: %v", err)
}
    1. 生成tocken
    if err := nodebootstraptokenphase.UpdateOrCreateToken(client, i.cfg.Token, false, i.cfg.TokenTTL.Duration, kubeadmconstants.DefaultTokenUsages, []string{kubeadmconstants.NodeBootstrapTokenAuthGroup}, tokenDescription); err != nil {
    return fmt.Errorf("error updating or creating token: %v", err)
}
    1. 调用clientgo创建dns和kube-proxy
    if err := dnsaddonphase.EnsureDNSAddon(i.cfg, client); err != nil {
    return fmt.Errorf("error ensuring dns addon: %v", err)
}

if err := proxyaddonphase.EnsureProxyAddon(i.cfg, client); err != nil {
    return fmt.Errorf("error ensuring proxy addon: %v", err)
}

    笔者批判代码无脑式的一个流程到底，要是笔者操刀定抽象成接口 RenderConf Save Run Clean等，DNS kube-porxy以及其它组件去实现，然后问题就是没把dns和kubeproxy的配置渲染出来，可能是它们不是static pod的原因, 然后就是join时的bug下文提到

    证书生成

    循环的调用了这一坨函数，我们只需要看其中一两个即可，其它的都差不多

    certActions := []func(cfg *kubeadmapi.MasterConfiguration) error{
    CreateCACertAndKeyfiles,
    CreateAPIServerCertAndKeyFiles,
    CreateAPIServerKubeletClientCertAndKeyFiles,
    CreateServiceAccountKeyAndPublicKeyFiles,
    CreateFrontProxyCACertAndKeyFiles,
    CreateFrontProxyClientCertAndKeyFiles,
}

    根证书生成：

    
//返回了根证书的公钥和私钥
func NewCACertAndKey() (*x509.Certificate, *rsa.PrivateKey, error) {

    caCert, caKey, err := pkiutil.NewCertificateAuthority()
    if err != nil {
        return nil, nil, fmt.Errorf("failure while generating CA certificate and key: %v", err)
    }

    return caCert, caKey, nil
}

    k8s.io/client-go/util/cert 这个库里面有两个函数，一个生成key的一个生成cert的：

    key, err := certutil.NewPrivateKey()
config := certutil.Config{
    CommonName: "kubernetes",
}
cert, err := certutil.NewSelfSignedCACert(config, key)

    config里面我们也可以填充一些别的证书信息：

    type Config struct {
    CommonName   string
    Organization []string
    AltNames     AltNames
    Usages       []x509.ExtKeyUsage
}

    私钥就是封装了rsa库里面的函数：

        "crypto/rsa"
    "crypto/x509"
func NewPrivateKey() (*rsa.PrivateKey, error) {
    return rsa.GenerateKey(cryptorand.Reader, rsaKeySize)
}

    自签证书,所以根证书里只有CommonName信息，Organization相当于没设置：

    func NewSelfSignedCACert(cfg Config, key *rsa.PrivateKey) (*x509.Certificate, error) {
    now := time.Now()
    tmpl := x509.Certificate{
        SerialNumber: new(big.Int).SetInt64(0),
        Subject: pkix.Name{
            CommonName:   cfg.CommonName,
            Organization: cfg.Organization,
        },
        NotBefore:             now.UTC(),
        NotAfter:              now.Add(duration365d * 10).UTC(),
        KeyUsage:              x509.KeyUsageKeyEncipherment | x509.KeyUsageDigitalSignature | x509.KeyUsageCertSign,
        BasicConstraintsValid: true,
        IsCA: true,
    }

    certDERBytes, err := x509.CreateCertificate(cryptorand.Reader, &tmpl, &tmpl, key.Public(), key)
    if err != nil {
        return nil, err
    }
    return x509.ParseCertificate(certDERBytes)
}

    生成好之后把之写入文件：

     pkiutil.WriteCertAndKey(pkiDir, baseName, cert, key);
certutil.WriteCert(certificatePath, certutil.EncodeCertPEM(cert))

    这里调用了pem库进行了编码

    encoding/pem

func EncodeCertPEM(cert *x509.Certificate) []byte {
    block := pem.Block{
        Type:  CertificateBlockType,
        Bytes: cert.Raw,
    }
    return pem.EncodeToMemory(&block)
}

    然后我们看apiserver的证书生成：

    caCert, caKey, err := loadCertificateAuthorithy(cfg.CertificatesDir, kubeadmconstants.CACertAndKeyBaseName)
//从根证书生成apiserver证书
apiCert, apiKey, err := NewAPIServerCertAndKey(cfg, caCert, caKey)

    这时需要关注AltNames了比较重要，所有需要访问master的地址域名都得加进去，对应配置文件中apiServerCertSANs字段,其它东西与根证书无差别

    config := certutil.Config{
    CommonName: kubeadmconstants.APIServerCertCommonName,
    AltNames:   *altNames,
    Usages:     []x509.ExtKeyUsage{x509.ExtKeyUsageServerAuth},
}

    创建k8s配置文件

    可以看到创建了这些文件

    return createKubeConfigFiles(
    outDir,
    cfg,
    kubeadmconstants.AdminKubeConfigFileName,
    kubeadmconstants.KubeletKubeConfigFileName,
    kubeadmconstants.ControllerManagerKubeConfigFileName,
    kubeadmconstants.SchedulerKubeConfigFileName,
)

    k8s封装了两个渲染配置的函数：
    区别是你的kubeconfig文件里会不会产生token，比如你进入dashboard需要一个token，或者你调用api需要一个token那么请生成带token的配置
    生成的conf文件基本一直只是比如ClientName这些东西不同，所以加密后的证书也不同，ClientName会被加密到证书里，然后k8s取出来当用户使用

    所以重点来了，我们做多租户时也要这样去生成。然后给该租户绑定角色。

    return kubeconfigutil.CreateWithToken(
    spec.APIServer,
    "kubernetes",
    spec.ClientName,
    certutil.EncodeCertPEM(spec.CACert),
    spec.TokenAuth.Token,
), nil

return kubeconfigutil.CreateWithCerts(
    spec.APIServer,
    "kubernetes",
    spec.ClientName,
    certutil.EncodeCertPEM(spec.CACert),
    certutil.EncodePrivateKeyPEM(clientKey),
    certutil.EncodeCertPEM(clientCert),
), nil

    然后就是填充Config结构体喽, 最后写到文件里，略

    "k8s.io/client-go/tools/clientcmd/api
return &clientcmdapi.Config{
    Clusters: map[string]*clientcmdapi.Cluster{
        clusterName: {
            Server: serverURL,
            CertificateAuthorityData: caCert,
        },
    },
    Contexts: map[string]*clientcmdapi.Context{
        contextName: {
            Cluster:  clusterName,
            AuthInfo: userName,
        },
    },
    AuthInfos:      map[string]*clientcmdapi.AuthInfo{},
    CurrentContext: contextName,
}

    创建static pod yaml文件

    这里返回了apiserver manager scheduler的pod结构体,

    specs := GetStaticPodSpecs(cfg, k8sVersion)
staticPodSpecs := map[string]v1.Pod{
    kubeadmconstants.KubeAPIServer: staticpodutil.ComponentPod(v1.Container{
        Name:          kubeadmconstants.KubeAPIServer,
        Image:         images.GetCoreImage(kubeadmconstants.KubeAPIServer, cfg.GetControlPlaneImageRepository(), cfg.KubernetesVersion, cfg.UnifiedControlPlaneImage),
        Command:       getAPIServerCommand(cfg, k8sVersion),
        VolumeMounts:  staticpodutil.VolumeMountMapToSlice(mounts.GetVolumeMounts(kubeadmconstants.KubeAPIServer)),
        LivenessProbe: staticpodutil.ComponentProbe(cfg, kubeadmconstants.KubeAPIServer, int(cfg.API.BindPort), "/healthz", v1.URISchemeHTTPS),
        Resources:     staticpodutil.ComponentResources("250m"),
        Env:           getProxyEnvVars(),
    }, mounts.GetVolumes(kubeadmconstants.KubeAPIServer)),
    kubeadmconstants.KubeControllerManager: staticpodutil.ComponentPod(v1.Container{
        Name:          kubeadmconstants.KubeControllerManager,
        Image:         images.GetCoreImage(kubeadmconstants.KubeControllerManager, cfg.GetControlPlaneImageRepository(), cfg.KubernetesVersion, cfg.UnifiedControlPlaneImage),
        Command:       getControllerManagerCommand(cfg, k8sVersion),
        VolumeMounts:  staticpodutil.VolumeMountMapToSlice(mounts.GetVolumeMounts(kubeadmconstants.KubeControllerManager)),
        LivenessProbe: staticpodutil.ComponentProbe(cfg, kubeadmconstants.KubeControllerManager, 10252, "/healthz", v1.URISchemeHTTP),
        Resources:     staticpodutil.ComponentResources("200m"),
        Env:           getProxyEnvVars(),
    }, mounts.GetVolumes(kubeadmconstants.KubeControllerManager)),
    kubeadmconstants.KubeScheduler: staticpodutil.ComponentPod(v1.Container{
        Name:          kubeadmconstants.KubeScheduler,
        Image:         images.GetCoreImage(kubeadmconstants.KubeScheduler, cfg.GetControlPlaneImageRepository(), cfg.KubernetesVersion, cfg.UnifiedControlPlaneImage),
        Command:       getSchedulerCommand(cfg),
        VolumeMounts:  staticpodutil.VolumeMountMapToSlice(mounts.GetVolumeMounts(kubeadmconstants.KubeScheduler)),
        LivenessProbe: staticpodutil.ComponentProbe(cfg, kubeadmconstants.KubeScheduler, 10251, "/healthz", v1.URISchemeHTTP),
        Resources:     staticpodutil.ComponentResources("100m"),
        Env:           getProxyEnvVars(),
    }, mounts.GetVolumes(kubeadmconstants.KubeScheduler)),
}

//获取特定版本的镜像
func GetCoreImage(image, repoPrefix, k8sVersion, overrideImage string) string {
    if overrideImage != "" {
        return overrideImage
    }
    kubernetesImageTag := kubeadmutil.KubernetesVersionToImageTag(k8sVersion)
    etcdImageTag := constants.DefaultEtcdVersion
    etcdImageVersion, err := constants.EtcdSupportedVersion(k8sVersion)
    if err == nil {
        etcdImageTag = etcdImageVersion.String()
    }
    return map[string]string{
        constants.Etcd:                  fmt.Sprintf("%s/%s-%s:%s", repoPrefix, "etcd", runtime.GOARCH, etcdImageTag),
        constants.KubeAPIServer:         fmt.Sprintf("%s/%s-%s:%s", repoPrefix, "kube-apiserver", runtime.GOARCH, kubernetesImageTag),
        constants.KubeControllerManager: fmt.Sprintf("%s/%s-%s:%s", repoPrefix, "kube-controller-manager", runtime.GOARCH, kubernetesImageTag),
        constants.KubeScheduler:         fmt.Sprintf("%s/%s-%s:%s", repoPrefix, "kube-scheduler", runtime.GOARCH, kubernetesImageTag),
    }[image]
}
//然后就把这个pod写到文件里了，比较简单
 staticpodutil.WriteStaticPodToDisk(componentName, manifestDir, spec);

    创建etcd的一样，不多废话

    等待kubelet启动成功

    这个错误非常容易遇到，看到这个基本就是kubelet没起来，我们需要检查：selinux swap 和Cgroup driver是不是一致
    setenforce 0 && swapoff -a && systemctl restart kubelet如果不行请保证 kubelet的Cgroup driver与docker一致，docker info|grep Cg

    go func(errC chan error, waiter apiclient.Waiter) {
    // This goroutine can only make kubeadm init fail. If this check succeeds, it won't do anything special
    if err := waiter.WaitForHealthyKubelet(40*time.Second, "http://localhost:10255/healthz"); err != nil {
        errC <- err
    }
}(errorChan, waiter)

go func(errC chan error, waiter apiclient.Waiter) {
    // This goroutine can only make kubeadm init fail. If this check succeeds, it won't do anything special
    if err := waiter.WaitForHealthyKubelet(60*time.Second, "http://localhost:10255/healthz/syncloop"); err != nil {
        errC <- err
    }
}(errorChan, waiter)

    创建DNS和kubeproxy

    我就是在此发现coreDNS的

    if features.Enabled(cfg.FeatureGates, features.CoreDNS) {
    return coreDNSAddon(cfg, client, k8sVersion)
}
return kubeDNSAddon(cfg, client, k8sVersion)

    然后coreDNS的yaml配置模板直接是写在代码里的：
    /app/phases/addons/dns/manifests.go

        CoreDNSDeployment = `
apiVersion: apps/v1beta2
kind: Deployment
metadata:
  name: coredns
  namespace: kube-system
  labels:
    k8s-app: kube-dns
spec:
  replicas: 1
  selector:
    matchLabels:
      k8s-app: kube-dns
  template:
    metadata:
      labels:
        k8s-app: kube-dns
    spec:
      serviceAccountName: coredns
      tolerations:
      - key: CriticalAddonsOnly
        operator: Exists
      - key: {{ .MasterTaintKey }}
...

    然后渲染模板，最后调用k8sapi创建,这种创建方式可以学习一下，虽然有点拙劣，这地方写的远不如kubectl好

    coreDNSConfigMap := &v1.ConfigMap{}
if err := kuberuntime.DecodeInto(legacyscheme.Codecs.UniversalDecoder(), configBytes, coreDNSConfigMap); err != nil {
    return fmt.Errorf("unable to decode CoreDNS configmap %v", err)
}

// Create the ConfigMap for CoreDNS or update it in case it already exists
if err := apiclient.CreateOrUpdateConfigMap(client, coreDNSConfigMap); err != nil {
    return err
}

coreDNSClusterRoles := &rbac.ClusterRole{}
if err := kuberuntime.DecodeInto(legacyscheme.Codecs.UniversalDecoder(), []byte(CoreDNSClusterRole), coreDNSClusterRoles); err != nil {
    return fmt.Errorf("unable to decode CoreDNS clusterroles %v", err)
}
...

    这里值得一提的是kubeproxy的configmap真应该把apiserver地址传入进来，允许自定义，因为做高可用时需要指定虚拟ip，得修改，很麻烦
    kubeproxy大差不差，不说了,想改的话改： app/phases/addons/proxy/manifests.go

    kubeadm join

    kubeadm join比较简单，一句话就可以说清楚，获取cluster info, 创建kubeconfig，怎么创建的kubeinit里面已经说了。带上token让kubeadm有权限
    可以拉取

    return https.RetrieveValidatedClusterInfo(cfg.DiscoveryFile)

cluster info内容
type Cluster struct {
    // LocationOfOrigin indicates where this object came from.  It is used for round tripping config post-merge, but never serialized.
    LocationOfOrigin string
    // Server is the address of the kubernetes cluster (https://hostname:port).
    Server string `json:"server"`
    // InsecureSkipTLSVerify skips the validity check for the server's certificate. This will make your HTTPS connections insecure.
    // +optional
    InsecureSkipTLSVerify bool `json:"insecure-skip-tls-verify,omitempty"`
    // CertificateAuthority is the path to a cert file for the certificate authority.
    // +optional
    CertificateAuthority string `json:"certificate-authority,omitempty"`
    // CertificateAuthorityData contains PEM-encoded certificate authority certificates. Overrides CertificateAuthority
    // +optional
    CertificateAuthorityData []byte `json:"certificate-authority-data,omitempty"`
    // Extensions holds additional information. This is useful for extenders so that reads and writes don't clobber unknown fields
    // +optional
    Extensions map[string]runtime.Object `json:"extensions,omitempty"`
}

return kubeconfigutil.CreateWithToken(
    clusterinfo.Server,
    "kubernetes",
    TokenUser,
    clusterinfo.CertificateAuthorityData,
    cfg.TLSBootstrapToken,
), nil

    CreateWithToken上文提到了不再赘述，这样就能去生成kubelet配置文件了，然后把kubelet启动起来即可

    kubeadm join的问题就是渲染配置时没有使用命令行传入的apiserver地址，而用clusterinfo里的地址，这不利于我们做高可用，可能我们传入一个虚拟ip，但是配置里还是apiser的地址

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