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

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：

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
 }

创建kubeconfig文件

 if err := kubeconfigphase.CreateInitKubeConfigFiles(kubeConfigDir, i.cfg); err != nil {
 return err
 }

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)
 }
}

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")
}

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)
}

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)
}

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

本文转自SegmentFault-kubeadm源码分析（kubernetes离线安装包，三步安装）

kubeadm源码分析（kubernetes离线安装包，三步安装）

kubeadm源码分析

kubeadm init

证书生成

创建k8s配置文件

创建static pod yaml文件

等待kubelet启动成功

创建DNS和kubeproxy

kubeadm join

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