Kubebuilder认证配置文件的加载

在kubernetes二次开发-Kubebuilder最佳实践中，我们简单使用了Kubebuilder来资源创建、验证等操作，那么你一定很好奇，程序是如何连接到api server做认证和鉴权的，下面我们来简单看下。

	mgr, err := ctrl.NewManager(ctrl.GetConfigOrDie(), ctrl.Options{
		Scheme:                 scheme,
		MetricsBindAddress:     metricsAddr,
		Port:                   9443,
		HealthProbeBindAddress: probeAddr,
		LeaderElection:         enableLeaderElection,
		LeaderElectionID:       "1de8eaa9.demo.kubebuilder.io",
	})

重点就在“ctrl.GetConfigOrDie()”中，追踪后，最终会来到这个地方：

sigs.k8s.io/controller-runtime/pkg/client/config/config.go


// loadConfig loads a REST Config as per the rules specified in GetConfig.
func loadConfig(context string) (*rest.Config, error) {
	// If a flag is specified with the config location, use that
	if len(kubeconfig) > 0 {
		return loadConfigWithContext("", &clientcmd.ClientConfigLoadingRules{ExplicitPath: kubeconfig}, context)
	}

	// If the recommended kubeconfig env variable is not specified,
	// try the in-cluster config.
	kubeconfigPath := os.Getenv(clientcmd.RecommendedConfigPathEnvVar)
	if len(kubeconfigPath) == 0 {
		if c, err := loadInClusterConfig(); err == nil {
			return c, nil
		}
	}

	// If the recommended kubeconfig env variable is set, or there
	// is no in-cluster config, try the default recommended locations.
	//
	// NOTE: For default config file locations, upstream only checks
	// $HOME for the user's home directory, but we can also try
	// os/user.HomeDir when $HOME is unset.
	//
	// TODO(jlanford): could this be done upstream?
	loadingRules := clientcmd.NewDefaultClientConfigLoadingRules()
	if _, ok := os.LookupEnv("HOME"); !ok {
		u, err := user.Current()
		if err != nil {
			return nil, fmt.Errorf("could not get current user: %v", err)
		}
		loadingRules.Precedence = append(loadingRules.Precedence, filepath.Join(u.HomeDir, clientcmd.RecommendedHomeDir, clientcmd.RecommendedFileName))
	}

	return loadConfigWithContext("", loadingRules, context)
}

该方法完成的功能如下：

（1）如果初始化了kubeconfig，则从kubeconfig中读取集群配置

（2）否则从环境变量KUBECONFIG读取，若没有则从集群内部读取，这种场景适用于部署到kubernetes中的场景，它是这样读取的：


// InClusterConfig returns a config object which uses the service account
// kubernetes gives to pods. It's intended for clients that expect to be
// running inside a pod running on kubernetes. It will return ErrNotInCluster
// if called from a process not running in a kubernetes environment.
func InClusterConfig() (*Config, error) {
    const (
        tokenFile  = "/var/run/secrets/kubernetes.io/serviceaccount/token"
        rootCAFile = "/var/run/secrets/kubernetes.io/serviceaccount/ca.crt"
    )
    host, port := os.Getenv("KUBERNETES_SERVICE_HOST"), os.Getenv("KUBERNETES_SERVICE_PORT")
    if len(host) == 0 || len(port) == 0 {
        return nil, ErrNotInCluster
    }

    token, err := ioutil.ReadFile(tokenFile)
    if err != nil {
        return nil, err
    }

    tlsClientConfig := TLSClientConfig{}

    if _, err := certutil.NewPool(rootCAFile); err != nil {
        klog.Errorf("Expected to load root CA config from %s, but got err: %v", rootCAFile, err)
    } else {
        tlsClientConfig.CAFile = rootCAFile
    }

    return &Config{
        // TODO: switch to using cluster DNS.
        Host:            "https://" + net.JoinHostPort(host, port),
        TLSClientConfig: tlsClientConfig,
        BearerToken:     string(token),
        BearerTokenFile: tokenFile,
    }, nil
}

读取POD上内“/var/run/secrets/kubernetes.io/serviceaccount/”下的“token”和“ca.crt”文件，如：

[root@master kubebuilder-demo]# kubectl get pods
NAME             READY   STATUS    RESTARTS   AGE
redis-sample-0   1/1     Running   0          25m
redis-sample-1   1/1     Running   0          25m
#
[root@master kubebuilder-demo]# kubectl exec -it redis-sample-0 -- sh
/data # ls -l /var/run/secrets/kubernetes.io/serviceaccount
total 0
lrwxrwxrwx    1 root     root            13 Feb 17 10:16 ca.crt -> ..data/ca.crt
lrwxrwxrwx    1 root     root            16 Feb 17 10:16 namespace -> ..data/namespace
lrwxrwxrwx    1 root     root            12 Feb 17 10:16 token -> ..data/token
/data # 
/data # cat /var/run/secrets/kubernetes.io/serviceaccount/token
eyJhbGciOiJSUzI1NiIsImtpZCI6IkxONVBTQm90R3JaT21ET3pkdmZhaWN1ak9lcGZ0WjRNemRudUhndjNmRGcifQ.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.xUf0OZxfTPitPgFF9AUKX439G_BJv5MDY25uTvpa8zj5QkZzaaV-238cZEpMU_cG3i2gtA_xfsw2nXKvfedmv1ZPbtcnovEVP-rCunO5DD8tSm478lsx0RxgzhJpvaVLxwyxwPeQyM8wcVPsXUvYt1ZvlemWWYqX739bRApHFsXIKtUhMAcvhz7byCfATBYLO0TFbrEUWNkT8y8ZDgqoogzRYs6cKi1thGuEaqF406Kt0GYUl06KjEAOdbzHyVpu-bsTz_OOZXWQVxSCquMrTZdffOK11DJrtADORPdavEQOde1Kf-LXaRdxh_-NbUVo9alFyfwiv9gegcUjXNHc6w/data # 
/data # cat /var/run/secrets/kubernetes.io/serviceaccount/ca.crt
-----BEGIN CERTIFICATE-----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-----END CERTIFICATE-----
/data #

（3）如果上面两个地方都没有找到，则会读取默认配置。即：$HOME下

//拼凑路径：
filepath.Join(u.HomeDir, clientcmd.RecommendedHomeDir, clientcmd.RecommendedFileName)//

const (
	RecommendedConfigPathFlag   = "kubeconfig"
	RecommendedConfigPathEnvVar = "KUBECONFIG"
	RecommendedHomeDir          = ".kube"
	RecommendedFileName         = "config"
	RecommendedSchemaName       = "schema"
)

下面是摘录自kubernetes文档中，关于在POD内访问api-server的一段描述，包含了如何访问API-Server，如何通过认证

While running in a Pod, the Kubernetes apiserver is accessible via a Service named kubernetes in the default namespace. Therefore, Pods can use the kubernetes.default.svc hostname to query the API server. Official client libraries do this automatically.
当应用运行在POD内部时，它会使用default命名空间下的名为“kubernetes”的service来访问API-Server，即使用kubernetes.default.svc来查询api-server

The recommended way to authenticate to the API server is with a service account credential. By default, a Pod is associated with a service account, and a credential (token) for that service account is placed into the filesystem tree of each container in that Pod, at /var/run/secrets/kubernetes.io/serviceaccount/token.

If available, a certificate bundle is placed into the filesystem tree of each container at /var/run/secrets/kubernetes.io/serviceaccount/ca.crt, and should be used to verify the serving certificate of the API server.

Finally, the default namespace to be used for namespaced API operations is placed in a file at /var/run/secrets/kubernetes.io/serviceaccount/namespace in each container

token、namespace和ca.crt，这三个文件是怎么被放入到POD中的？
这些token、namespace和ca.crt是通过投射的方式，放入到POD中的，有关于该过程的详细解释见：https://kubernetes.io/docs/reference/access-authn-authz/service-accounts-admin/#bound-service-account-token-volume

token、namespace和ca.crt，这三个文件的作用？
这三个文件由于参与到Pod进程与API Server认证的过程中，起到了类似secret（私密凭据）的作用，所以它们被称为Kubernetes Secret对象。Secret从属于Service Account资源对象，属于Service Account的一部分，在一个Service Account对象里面可以包括多个不同的Secret对象，分别用于不同目的的认证活动。
更多细节，可以查看《kubernetes权威指南第5版- 6.4节　Service Account》

有关token，如何在认证过程中发挥作用？
Pod中的客户端调用Kubernetes API时，在HTTP Header中传递了一个Token字符串，这类似于之前提到的HTTP Token认证方式，但有以下几个不同之处。
◎　这个Token的内容来自Pod里指定路径下的一个文件（/run/secrets/kubernetes.io/serviceaccount/token），这种Token是动态生成的，确切地说，是由Kubernetes Controller进程用API Server的私钥（--service-account-private-key-file指定的私钥）签名生成的一个JWT Secret。
◎　在官方提供的客户端REST框架代码里，通过HTTPS方式与APIServer建立连接后，会用Pod里指定路径下的一个CA证书（/run/secrets/kubernetes.io/serviceaccount/ca.crt）验证API Server发来的证书，验证是否为CA证书签名的合法证书。
◎　API Server在收到这个Token以后，采用自己的私钥（实际上是使用service-accountkey-file参数指定的私钥，如果没有设置此参数，则默认采用tls-private-key-file指定的参数，即自己的私钥）对Token进行合法性验证。

posted @ 2022-02-17 20:50 cosmoswong 阅读(774) 评论(0) 编辑收藏举报

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