BACKGROUND
admission controllers的特点：
- 可定制性：准入功能可针对不同的场景进行调整。
- 可预防性：审计则是为了检测问题，而准入控制器可以预防问题发生
- 可扩展性：在kubernetes自有的验证机制外，增加了另外的防线，弥补了RBAC仅能对资源提供安全保证。
下图，显示了用户操作资源的流程，可以看出 admission controllers 作用是在通过身份验证资源持久化之前起到拦截作用。在准入控制器的加入会使kubernetes增加了更高级的安全功能。
这里找到一个大佬博客画的图，通过两张图可以很清晰的了解到admission webhook流程，与官方给出的不一样的地方在于，这里清楚地定位了kubernetes admission webhook 处于准入控制中，RBAC之后，push 之前。
两种控制器有什么区别？
根据官方提供的说法是
Mutating controllers may modify related objects to the requests they admit; validating controllers may not
从结构图中也可以看出，validating 是在持久化之前，而 Mutating 是在结构验证前，根据这些特性我们可以使用 Mutating 修改这个资源对象内容（如增加验证的信息），在 validating 中验证是否合法。
composition of admission controllers
kubernetes中的 admission controllers 由两部分组成：
- 内置在APIServer中的准入控制器 build-in list
- 特殊的控制器；也是内置在APIServer中，但提供一些自定义的功能
- MutatingAdmission
- ValidatingAdmission
Mutating 控制器可以修改他们处理的资源对象，Validating 控制器不会。当在任何一个阶段中的任何控制器拒绝这个了请求，则会立即拒绝整个请求，并将错误返回。
admission webhook
由于准入控制器是内置在 kube-apiserver 中的，这种情况下就限制了admission controller的可扩展性。在这种背景下，kubernetes提供了一种可扩展的准入控制器 extensible admission controllers，这种行为叫做动态准入控制 Dynamic Admission Control，而提供这个功能的就是 admission webhook 。
admission webhook 通俗来讲就是 HTTP 回调，通过定义一个http server，接收准入请求并处理。用户可以通过kubernetes提供的两种类型的 admission webhook，validating admission webhook 和 mutating admission webhook。来完成自定义的准入策略的处理。
webhook 就是
注：从上面的流程图也可以看出，admission webhook 也是有顺序的。首先调用mutating webhook，然后会调用validating webhook。
如何使用准入控制器
使用条件：kubernetes v1.16 使用 admissionregistration.k8s.io/v1 ；kubernetes v1.9 使用 admissionregistration.k8s.io/v1beta1。
如何在集群中开启准入控制器? ：查看kube-apiserver 的启动参数 --enable-admission-plugins ；通过该参数来配置要启动的准入控制器，如 --enable-admission-plugins=NodeRestriction 多个准入控制器以 , 分割，顺序无关紧要。 反之使用 --disable-admission-plugins 参数可以关闭相应的准入控制器（Refer to apiserver opts）。
通过 kubectl 命令可以看到，当前kubernetes集群所支持准入控制器的版本
$ kubectl api-versions | grep admissionregistration.k8s.io/v1 admissionregistration.k8s.io/v1 admissionregistration.k8s.io/v1beta1 webhook工作原理
通过上面的学习，已经了解到了两种webhook的工作原理如下所示：
mutating webhook，会在持久化前拦截在 MutatingWebhookConfiguration 中定义的规则匹配的请求。MutatingAdmissionWebhook 通过向 mutating webhook 服务器发送准入请求来执行验证。
validaing webhook，会在持久化前拦截在
ValidatingWebhookConfiguration中定义的规则匹配的请求。ValidatingAdmissionWebhook 通过将准入请求发送到 validating webhook server来执行验证。
那么接下来将从源码中看这个在这个工作流程中，究竟做了些什么？
资源类型
对于 1.9 版本之后，也就是 v1 版本 ，admission 被定义在 k8s.ioapiadmissionregistrationv1types.go ，大同小异，因为本地只有1.18集群，所以以这个讲解。
对于 Validating Webhook 来讲实现主要都在webhook中
type ValidatingWebhookConfiguration struct { // 每个api必须包含下列的metadata，这个是kubernetes规范，可以在注释中的url看到相关文档 metav1.TypeMeta `json:",inline"` metav1.ObjectMeta `json:"metadata,omitempty" protobuf:"bytes,1,opt,name=metadata"` // Webhooks在这里被表示为[]ValidatingWebhook，表示我们可以注册多个 // +optional // +patchMergeKey=name // +patchStrategy=merge Webhooks []ValidatingWebhook `json:"webhooks,omitempty" patchStrategy:"merge" patchMergeKey:"name" protobuf:"bytes,2,rep,name=Webhooks"` } webhook，则是对这种类型的webhook提供的操作、资源等。对于这部分不做过多的注释了，因为这里本身为kubernetes API资源，官网有很详细的例子与说明。这里更多字段的意思的可以参考官方 doc
type ValidatingWebhook struct { // admission webhook的名词，Required Name string `json:"name" protobuf:"bytes,1,opt,name=name"` // ClientConfig 定义了与webhook通讯的方式 Required ClientConfig WebhookClientConfig `json:"clientConfig" protobuf:"bytes,2,opt,name=clientConfig"` // rule表示了webhook对于哪些资源及子资源的操作进行关注 Rules []RuleWithOperations `json:"rules,omitempty" protobuf:"bytes,3,rep,name=rules"` // FailurePolicy 对于无法识别的value将如何处理，allowed/Ignore optional FailurePolicy *FailurePolicyType `json:"failurePolicy,omitempty" protobuf:"bytes,4,opt,name=failurePolicy,casttype=FailurePolicyType"` // matchPolicy 定义了如何使用“rules”列表来匹配传入的请求。 MatchPolicy *MatchPolicyType `json:"matchPolicy,omitempty" protobuf:"bytes,9,opt,name=matchPolicy,casttype=MatchPolicyType"` NamespaceSelector *metav1.LabelSelector `json:"namespaceSelector,omitempty" protobuf:"bytes,5,opt,name=namespaceSelector"` SideEffects *SideEffectClass `json:"sideEffects" protobuf:"bytes,6,opt,name=sideEffects,casttype=SideEffectClass"` AdmissionReviewVersions []string `json:"admissionReviewVersions" protobuf:"bytes,8,rep,name=admissionReviewVersions"` } 到这里了解了一个webhook资源的定义，那么这个如何使用呢？通过 Find Usages 找到一个 k8s.io/apiserver/pkg/admission/plugin/webhook/accessors.go 在使用它。这里没有注释，但在结构上可以看出，包含客户端与一系列选择器组成
type mutatingWebhookAccessor struct { *v1.MutatingWebhook uid string configurationName string initObjectSelector sync.Once objectSelector labels.Selector objectSelectorErr error initNamespaceSelector sync.Once namespaceSelector labels.Selector namespaceSelectorErr error initClient sync.Once client *rest.RESTClient clientErr error } accessor 因为包含了整个webhookconfig定义的一些动作（这里个人这么觉得）。
accessor.go 下面 有一个 GetRESTClient 方法 ，通过这里可以看出，这里做的就是使用根据 accessor 构造一个客户端。
func (m *mutatingWebhookAccessor) GetRESTClient(clientManager *webhookutil.ClientManager) (*rest.RESTClient, error) { m.initClient.Do(func() { m.client, m.clientErr = clientManager.HookClient(hookClientConfigForWebhook(m)) }) return m.client, m.clientErr } 到这步骤已经没必要往下看了，因已经知道这里是请求webhook前的步骤了，下面就是何时请求了。
k8s.ioapiserverpkgadmissionpluginwebhookvalidatingdispatcher.go 下面有两个方法，Dispatch去请求我们自己定义的webhook
func (d *validatingDispatcher) Dispatch(ctx context.Context, attr admission.Attributes, o admission.ObjectInterfaces, hooks []webhook.WebhookAccessor) error { var relevantHooks []*generic.WebhookInvocation // Construct all the versions we need to call our webhooks versionedAttrs := map[schema.GroupVersionKind]*generic.VersionedAttributes{} for _, hook := range hooks { invocation, statusError := d.plugin.ShouldCallHook(hook, attr, o) if statusError != nil { return statusError } if invocation == nil { continue } relevantHooks = append(relevantHooks, invocation) // If we already have this version, continue if _, ok := versionedAttrs[invocation.Kind]; ok { continue } versionedAttr, err := generic.NewVersionedAttributes(attr, invocation.Kind, o) if err != nil { return apierrors.NewInternalError(err) } versionedAttrs[invocation.Kind] = versionedAttr } if len(relevantHooks) == 0 { // no matching hooks return nil } // Check if the request has already timed out before spawning remote calls select { case <-ctx.Done(): // parent context is canceled or timed out, no point in continuing return apierrors.NewTimeoutError("request did not complete within requested timeout", 0) default: } wg := sync.WaitGroup{} errCh := make(chan error, len(relevantHooks)) wg.Add(len(relevantHooks)) // 循环所有相关的注册的hook for i := range relevantHooks { go func(invocation *generic.WebhookInvocation) { defer wg.Done() // invacation 中有一个 Accessor,Accessor注册了一个相关的webhookconfig // 也就是我们 kubectl -f 注册进来的那个webhook的相关配置 hook, ok := invocation.Webhook.GetValidatingWebhook() if !ok { utilruntime.HandleError(fmt.Errorf("validating webhook dispatch requires v1.ValidatingWebhook, but got %T", hook)) return } versionedAttr := versionedAttrs[invocation.Kind] t := time.Now() // 调用了callHook去请求我们自定义的webhook err := d.callHook(ctx, hook, invocation, versionedAttr) ignoreClientCallFailures := hook.FailurePolicy != nil && *hook.FailurePolicy == v1.Ignore rejected := false if err != nil { switch err := err.(type) { case *webhookutil.ErrCallingWebhook: if !ignoreClientCallFailures { rejected = true admissionmetrics.Metrics.ObserveWebhookRejection(hook.Name, "validating", string(versionedAttr.Attributes.GetOperation()), admissionmetrics.WebhookRejectionCallingWebhookError, 0) } case *webhookutil.ErrWebhookRejection: rejected = true admissionmetrics.Metrics.ObserveWebhookRejection(hook.Name, "validating", string(versionedAttr.Attributes.GetOperation()), admissionmetrics.WebhookRejectionNoError, int(err.Status.ErrStatus.Code)) default: rejected = true admissionmetrics.Metrics.ObserveWebhookRejection(hook.Name, "validating", string(versionedAttr.Attributes.GetOperation()), admissionmetrics.WebhookRejectionAPIServerInternalError, 0) } } admissionmetrics.Metrics.ObserveWebhook(time.Since(t), rejected, versionedAttr.Attributes, "validating", hook.Name) if err == nil { return } if callErr, ok := err.(*webhookutil.ErrCallingWebhook); ok { if ignoreClientCallFailures { klog.Warningf("Failed calling webhook, failing open %v: %v", hook.Name, callErr) utilruntime.HandleError(callErr) return } klog.Warningf("Failed calling webhook, failing closed %v: %v", hook.Name, err) errCh <- apierrors.NewInternalError(err) return } if rejectionErr, ok := err.(*webhookutil.ErrWebhookRejection); ok { err = rejectionErr.Status } klog.Warningf("rejected by webhook %q: %#v", hook.Name, err) errCh <- err }(relevantHooks[i]) } wg.Wait() close(errCh) var errs []error for e := range errCh { errs = append(errs, e) } if len(errs) == 0 { return nil } if len(errs) > 1 { for i := 1; i < len(errs); i++ { // TODO: merge status errors; until then, just return the first one. utilruntime.HandleError(errs[i]) } } return errs[0] } callHook 可以理解为真正去请求我们自定义的webhook服务的动作
func (d *validatingDispatcher) callHook(ctx context.Context, h *v1.ValidatingWebhook, invocation *generic.WebhookInvocation, attr *generic.VersionedAttributes) error { if attr.Attributes.IsDryRun() { if h.SideEffects == nil { return &webhookutil.ErrCallingWebhook{WebhookName: h.Name, Reason: fmt.Errorf("Webhook SideEffects is nil")} } if !(*h.SideEffects == v1.SideEffectClassNone || *h.SideEffects == v1.SideEffectClassNoneOnDryRun) { return webhookerrors.NewDryRunUnsupportedErr(h.Name) } } uid, request, response, err := webhookrequest.CreateAdmissionObjects(attr, invocation) if err != nil { return &webhookutil.ErrCallingWebhook{WebhookName: h.Name, Reason: err} } // 发生请求，可以看到，这里从上面的讲到的地方获取了一个客户端 client, err := invocation.Webhook.GetRESTClient(d.cm) if err != nil { return &webhookutil.ErrCallingWebhook{WebhookName: h.Name, Reason: err} } trace := utiltrace.New("Call validating webhook", utiltrace.Field{"configuration", invocation.Webhook.GetConfigurationName()}, utiltrace.Field{"webhook", h.Name}, utiltrace.Field{"resource", attr.GetResource()}, utiltrace.Field{"subresource", attr.GetSubresource()}, utiltrace.Field{"operation", attr.GetOperation()}, utiltrace.Field{"UID", uid}) defer trace.LogIfLong(500 * time.Millisecond) // 这里设置超时，超时时长就是在yaml资源清单中设置的那个值 if h.TimeoutSeconds != nil { var cancel context.CancelFunc ctx, cancel = context.WithTimeout(ctx, time.Duration(*h.TimeoutSeconds)*time.Second) defer cancel() } // 直接用post请求我们自己定义的webhook接口 r := client.Post().Body(request) // if the context has a deadline, set it as a parameter to inform the backend if deadline, hasDeadline := ctx.Deadline(); hasDeadline { // compute the timeout if timeout := time.Until(deadline); timeout > 0 { // if it's not an even number of seconds, round up to the nearest second if truncated := timeout.Truncate(time.Second); truncated != timeout { timeout = truncated + time.Second } // set the timeout r.Timeout(timeout) } } if err := r.Do(ctx).Into(response); err != nil { return &webhookutil.ErrCallingWebhook{WebhookName: h.Name, Reason: err} } trace.Step("Request completed") result, err := webhookrequest.VerifyAdmissionResponse(uid, false, response) if err != nil { return &webhookutil.ErrCallingWebhook{WebhookName: h.Name, Reason: err} } for k, v := range result.AuditAnnotations { key := h.Name + "/" + k if err := attr.Attributes.AddAnnotation(key, v); err != nil { klog.Warningf("Failed to set admission audit annotation %s to %s for validating webhook %s: %v", key, v, h.Name, err) } } if result.Allowed { return nil } return &webhookutil.ErrWebhookRejection{Status: webhookerrors.ToStatusErr(h.Name, result.Result)} } 走到这里基本上对 admission webhook 有了大致的了解，可以知道这个操作是由 apiserver 完成的。下面就实际操作下自定义一个webhook。
这里还有两个概念，就是请求参数 AdmissionRequest 和相应参数 AdmissionResponse，这些可以在 callHook 中看到，这两个参数被定义在 k8s.ioapiadmissionv1types.go ；这两个参数也就是我们在自定义 webhook 时需要处理接收到的body的结构，以及我们响应内容数据结构。
如何编写一个自定义的admission webhook
通过上面的学习了解到了，自定义的webhook就是做为kubernetes提供给用户两种admission controller来验证自定义业务的一个中间件 admission webhook。本质上他是一个HTTP Server，用户可以使用任何语言来完成这部分功能。当然，如果涉及到需要对kubernetes集群资源操作的话，还是建议使用kubernetes官方提供了SDK的编程语言来完成自定义的webhook。
那么完成一个自定义admission webhook需要两个步骤：
- 将相关的webhook config注册给kubernetes，也就是让kubernetes知道你的webhook
- 准备一个http server来处理 apiserver发过来验证的信息
注：这里使用go net/http包，本身不区分方法处理HTTP的何种请求，如果用其他框架实现的，如django，需要指定对应方法需要为POST
向kubernetes注册webhook对象
kubernetes提供的两种类型可自定义的准入控制器，和其他资源一样，可以利用资源清单，动态配置那些资源要被adminssion webhook处理。 kubernetes将这种形式抽象为两种资源：
-
ValidatingWebhookConfiguration
-
MutatingWebhookConfiguration
ValidatingAdmission
apiVersion: admissionregistration.k8s.io/v1 kind: ValidatingWebhookConfiguration metadata: name: "pod-policy.example.com" webhooks: - name: "pod-policy.example.com" rules: - apiGroups: [""] # 拦截资源的Group "" 表示 core。"*" 表示所有。 apiVersions: ["v1"] # 拦截资源的版本 operations: ["CREATE"] # 什么请求下拦截 resources: ["pods"] # 拦截什么资源 scope: "Namespaced" # 生效的范围，cluster还是namespace "*"表示没有范围限制。 clientConfig: # 我们部署的webhook服务， service: # service是在cluster-in模式下 namespace: "example-namespace" name: "example-service" port: 443 # 服务的端口 path: "/validate" # path是对应用于验证的接口 # caBundle是提供给 admission webhook CA证书 caBundle: "Ci0tLS0tQk...<base64-encoded PEM bundle containing the CA that signed the webhook's serving certificate>...tLS0K" admissionReviewVersions: ["v1", "v1beta1"] sideEffects: None timeoutSeconds: 5 # 1-30s直接，表示请求api的超时时间 MutatingAdmission
apiVersion: admissionregistration.k8s.io/v1 kind: ValidatingWebhookConfiguration metadata: name: "valipod-policy.example.com" webhooks: - name: "valipod-policy.example.com" rules: - apiGroups: ["apps"] # 拦截资源的Group "" 表示 core。"*" 表示所有。 apiVersions: ["v1"] # 拦截资源的版本 operations: ["CREATE"] # 什么请求下拦截 resources: ["deployments"] # 拦截什么资源 scope: "Namespaced" # 生效的范围，cluster还是namespace "*"表示没有范围限制。 clientConfig: # 我们部署的webhook服务， url: "https://10.0.0.1:81/validate" # 这里是外部模式 # service: # service是在cluster-in模式下 # namespace: "default" # name: "admission-webhook" # port: 81 # 服务的端口 # path: "/mutate" # path是对应用于验证的接口 # caBundle是提供给 admission webhook CA证书 caBundle: "Ci0tLS0tQk...<base64-encoded PEM bundle containing the CA that signed the webhook's serving certificate>...tLS0K" admissionReviewVersions: ["v1"] sideEffects: None timeoutSeconds: 5 # 1-30s直接，表示请求api的超时时间 注：对于webhook，也可以引入外部的服务，并非必须部署到集群内部
对于外部服务来讲，需要 clientConfig 中的 service , 更换为 url ; 通过 url 参数可以将一个外部的服务引入
apiVersion: admissionregistration.k8s.io/v1 kind: MutatingWebhookConfiguration ... webhooks: - name: my-webhook.example.com clientConfig: url: "https://my-webhook.example.com:9443/my-webhook-path" ... 注：这里的url规则必须准守下列形式：
scheme://host:port/path- 使用了url 时，这里不应填写集群内的服务
scheme必须是 https，不能为http，这就意味着，引入外部时也需要- 配置时使用了，
?xx=xx的参数也是不被允许的（官方说法是这样的，通过源码学习了解到因为会发送特定的请求体，所以无需管参数）
更多的配置可以参考kubernetes官方提供的 doc
准备一个webhook
让我们编写我们的 webhook server。将创建两个钩子，/mutate 与 /validate；
/mutate将在创建deployment资源时，基于版本，给资源加上注释webhook.example.com/allow: true/validate将对/mutate增加的allow:true那么则继续，否则拒绝。
这里为了方便，全部写在一起了，实际上不符合软件的设计。在kubernetes代码库中也提供了一个webhook server，可以参考他这个webhook server来学习具体要做什么
package main import ( "context" "crypto/tls" "encoding/json" "fmt" "io/ioutil" "net/http" "os" "os/signal" "strings" "syscall" v1admission "k8s.io/api/admission/v1" "k8s.io/apimachinery/pkg/runtime" "k8s.io/apimachinery/pkg/runtime/serializer" appv1 "k8s.io/api/apps/v1" metav1 "k8s.io/apimachinery/pkg/apis/meta/v1" "k8s.io/klog" ) type patch struct { Op string `json:"op"` Path string `json:"path"` Value map[string]string `json:"value"` } func serve(w http.ResponseWriter, r *http.Request) { var body []byte if data, err := ioutil.ReadAll(r.Body); err == nil { body = data } klog.Infof(fmt.Sprintf("receive request: %v....", string(body)[:130])) if len(body) == 0 { klog.Error(fmt.Sprintf("admission request body is empty")) http.Error(w, fmt.Errorf("admission request body is empty").Error(), http.StatusBadRequest) return } var admission v1admission.AdmissionReview codefc := serializer.NewCodecFactory(runtime.NewScheme()) decoder := codefc.UniversalDeserializer() _, _, err := decoder.Decode(body, nil, &admission) if err != nil { msg := fmt.Sprintf("Request could not be decoded: %v", err) klog.Error(msg) http.Error(w, msg, http.StatusBadRequest) return } if admission.Request == nil { klog.Error(fmt.Sprintf("admission review can't be used: Request field is nil")) http.Error(w, fmt.Errorf("admission review can't be used: Request field is nil").Error(), http.StatusBadRequest) return } switch strings.Split(r.RequestURI, "?")[0] { case "/mutate": req := admission.Request var admissionResp v1admission.AdmissionReview admissionResp.APIVersion = admission.APIVersion admissionResp.Kind = admission.Kind klog.Infof("AdmissionReview for Kind=%v, Namespace=%v Name=%v UID=%v Operation=%v", req.Kind.Kind, req.Namespace, req.Name, req.UID, req.Operation) switch req.Kind.Kind { case "Deployment": var ( respstr []byte err error deploy appv1.Deployment ) if err = json.Unmarshal(req.Object.Raw, &deploy); err != nil { respStructure := v1admission.AdmissionResponse{Result: &metav1.Status{ Message: fmt.Sprintf("could not unmarshal resouces review request: %v", err), Code: http.StatusInternalServerError, }} klog.Error(fmt.Sprintf("could not unmarshal resouces review request: %v", err)) if respstr, err = json.Marshal(respStructure); err != nil { klog.Error(fmt.Errorf("could not unmarshal resouces review response: %v", err)) http.Error(w, fmt.Errorf("could not unmarshal resouces review response: %v", err).Error(), http.StatusInternalServerError) return } http.Error(w, string(respstr), http.StatusBadRequest) return } current_annotations := deploy.GetAnnotations() pl := []patch{} for k, v := range current_annotations { pl = append(pl, patch{ Op: "add", Path: "/metadata/annotations", Value: map[string]string{ k: v, }, }) } pl = append(pl, patch{ Op: "add", Path: "/metadata/annotations", Value: map[string]string{ deploy.Name + "/Allow": "true", }, }) annotationbyte, err := json.Marshal(pl) if err != nil { http.Error(w, err.Error(), http.StatusInternalServerError) return } respStructure := &v1admission.AdmissionResponse{ UID: req.UID, Allowed: true, Patch: annotationbyte, PatchType: func() *v1admission.PatchType { t := v1admission.PatchTypeJSONPatch return &t }(), Result: &metav1.Status{ Message: fmt.Sprintf("could not unmarshal resouces review request: %v", err), Code: http.StatusOK, }, } admissionResp.Response = respStructure klog.Infof("sending response: %s....", admissionResp.Response.String()[:130]) respByte, err := json.Marshal(admissionResp) if err != nil { klog.Errorf("Can't encode response messages: %v", err) http.Error(w, err.Error(), http.StatusInternalServerError) } klog.Infof("prepare to write response...") w.Header().Set("Content-Type", "application/json") if _, err := w.Write(respByte); err != nil { klog.Errorf("Can't write response: %v", err) http.Error(w, fmt.Sprintf("could not write response: %v", err), http.StatusInternalServerError) } default: klog.Error(fmt.Sprintf("unsupport resouces review request type")) http.Error(w, "unsupport resouces review request type", http.StatusBadRequest) } case "/validate": req := admission.Request var admissionResp v1admission.AdmissionReview admissionResp.APIVersion = admission.APIVersion admissionResp.Kind = admission.Kind klog.Infof("AdmissionReview for Kind=%v, Namespace=%v Name=%v UID=%v Operation=%v", req.Kind.Kind, req.Namespace, req.Name, req.UID, req.Operation) var ( deploy appv1.Deployment respstr []byte ) switch req.Kind.Kind { case "Deployment": if err = json.Unmarshal(req.Object.Raw, &deploy); err != nil { respStructure := v1admission.AdmissionResponse{Result: &metav1.Status{ Message: fmt.Sprintf("could not unmarshal resouces review request: %v", err), Code: http.StatusInternalServerError, }} klog.Error(fmt.Sprintf("could not unmarshal resouces review request: %v", err)) if respstr, err = json.Marshal(respStructure); err != nil { klog.Error(fmt.Errorf("could not unmarshal resouces review response: %v", err)) http.Error(w, fmt.Errorf("could not unmarshal resouces review response: %v", err).Error(), http.StatusInternalServerError) return } http.Error(w, string(respstr), http.StatusBadRequest) return } } al := deploy.GetAnnotations() respStructure := v1admission.AdmissionResponse{ UID: req.UID, } if al[fmt.Sprintf("%s/Allow", deploy.Name)] == "true" { respStructure.Allowed = true respStructure.Result = &metav1.Status{ Code: http.StatusOK, } } else { respStructure.Allowed = false respStructure.Result = &metav1.Status{ Code: http.StatusForbidden, Reason: func() metav1.StatusReason { return metav1.StatusReasonForbidden }(), Message: fmt.Sprintf("the resource %s couldn't to allow entry.", deploy.Kind), } } admissionResp.Response = &respStructure klog.Infof("sending response: %s....", admissionResp.Response.String()[:130]) respByte, err := json.Marshal(admissionResp) if err != nil { klog.Errorf("Can't encode response messages: %v", err) http.Error(w, err.Error(), http.StatusInternalServerError) } klog.Infof("prepare to write response...") w.Header().Set("Content-Type", "application/json") if _, err := w.Write(respByte); err != nil { klog.Errorf("Can't write response: %v", err) http.Error(w, fmt.Sprintf("could not write response: %v", err), http.StatusInternalServerError) } } } func main() { var ( cert, key string ) if cert = os.Getenv("TLS_CERT"); len(cert) == 0 { cert = "./tls/tls.crt" } if key = os.Getenv("TLS_KEY"); len(key) == 0 { key = "./tls/tls.key" } ca, err := tls.LoadX509KeyPair(cert, key) if err != nil { klog.Error(err.Error()) return } server := &http.Server{ Addr: ":81", TLSConfig: &tls.Config{ Certificates: []tls.Certificate{ ca, }, }, } httpserver := http.NewServeMux() httpserver.HandleFunc("/validate", serve) httpserver.HandleFunc("/mutate", serve) httpserver.HandleFunc("/ping", func(w http.ResponseWriter, r *http.Request) { klog.Info(fmt.Sprintf("%s %s", r.RequestURI, "pong")) fmt.Fprint(w, "pong") }) server.Handler = httpserver go func() { if err := server.ListenAndServeTLS("", ""); err != nil { klog.Errorf("Failed to listen and serve webhook server: %v", err) } }() klog.Info("starting serve.") signalChan := make(chan os.Signal, 1) signal.Notify(signalChan, syscall.SIGINT, syscall.SIGTERM) <-signalChan klog.Infof("Got shut signal, shutting...") if err := server.Shutdown(context.Background()); err != nil { klog.Errorf("HTTP server Shutdown: %v", err) } } 对应的Dockerfile
FROM golang:alpine AS builder MAINTAINER cylon WORKDIR /admission COPY ./ /admission ENV GOPROXY https://goproxy.cn,direct RUN sed -i 's/dl-cdn.alpinelinux.org/mirrors.ustc.edu.cn/g' /etc/apk/repositories && apk add upx && GOOS=linux GOARCH=amd64 CGO_ENABLED=0 go build -ldflags "-s -w" -o webhook main.go && upx -1 webhook && chmod +x webhook FROM alpine AS runner WORKDIR /go/admission COPY --from=builder /admission/webhook . VOLUME ["/admission"] 集群内部部署所需的资源清单
apiVersion: v1 kind: Service metadata: name: admission-webhook labels: app: admission-webhook spec: ports: - port: 81 targetPort: 81 selector: app: simple-webhook --- apiVersion: apps/v1 kind: Deployment metadata: labels: app: simple-webhook name: simple-webhook spec: replicas: 1 selector: matchLabels: app: simple-webhook template: metadata: labels: app: simple-webhook spec: containers: - image: cylonchau/simple-webhook:v0.0.2 imagePullPolicy: IfNotPresent name: webhook command: ["./webhook"] env: - name: "TLS_CERT" value: "./tls/tls.crt" - name: "TLS_KEY" value: "./tls/tls.key" - name: NS_NAME valueFrom: fieldRef: apiVersion: v1 fieldPath: metadata.namespace ports: - containerPort: 81 volumeMounts: - name: tlsdir mountPath: /go/admission/tls readOnly: true volumes: - name: tlsdir secret: secretName: webhook --- apiVersion: admissionregistration.k8s.io/v1 kind: MutatingWebhookConfiguration metadata: name: "pod-policy.example.com" webhooks: - name: "pod-policy.example.com" rules: - apiGroups: ["apps"] # 拦截资源的Group "" 表示 core。"*" 表示所有。 apiVersions: ["v1"] # 拦截资源的版本 operations: ["CREATE"] # 什么请求下拦截 resources: ["deployments"] # 拦截什么资源 scope: "Namespaced" # 生效的范围，cluster还是namespace "*"表示没有范围限制。 clientConfig: # 我们部署的webhook服务， url: "https://10.0.0.1:81/mutate" # service: # service是在cluster-in模式下 # namespace: "default" # name: "admission-webhook" # port: 81 # 服务的端口 # path: "/mutate" # path是对应用于验证的接口 # caBundle是提供给 admission webhook CA证书 caBundle: Put you CA (base64 encode) in here admissionReviewVersions: ["v1"] sideEffects: None timeoutSeconds: 5 # 1-30s直接，表示请求api的超时时间 --- apiVersion: admissionregistration.k8s.io/v1 kind: ValidatingWebhookConfiguration metadata: name: "valipod-policy.example.com" webhooks: - name: "valipod-policy.example.com" rules: - apiGroups: ["apps"] # 拦截资源的Group "" 表示 core。"*" 表示所有。 apiVersions: ["v1"] # 拦截资源的版本 operations: ["CREATE"] # 什么请求下拦截 resources: ["deployments"] # 拦截什么资源 scope: "Namespaced" # 生效的范围，cluster还是namespace "*"表示没有范围限制。 clientConfig: # 我们部署的webhook服务， # service: # service是在cluster-in模式下 # namespace: "default" # name: "admission-webhook" # port: 81 # 服务的端口 # path: "/mutate" # path是对应用于验证的接口 # caBundle是提供给 admission webhook CA证书 caBundle: Put you CA (base64 encode) in here admissionReviewVersions: ["v1"] sideEffects: None timeoutSeconds: 5 # 1-30s直接，表示请求api的超时时间 这里需要主义的问题
证书问题
如果需要 cluster-in ，那么则需要对对应webhookconfig资源配置 service ；如果使用的是外部部署，则需要配置对应访问地址，如："https://xxxx:port/method"
这两种方式的证书均需要对应的 subjectAltName ，cluster-in 模式 需要对应service名称，如，至少包含serviceName.NS.svc 这一个域名。
下面就是证书类问题的错误
Failed calling webhook, failing closed pod-policy.example.com: failed calling webhook "pod-policy.example.com": Post https://admission-webhook.default.svc:81/mutate?timeout=5s: x509: certificate signed by unknown authority (possibly because of "crypto/rsa: verification error" while trying to verify candidate authority certificate "admission-webhook-ca") 相应信息问题
上面我们了解到的APIServer是去发出 v1admission.AdmissionReview 也就是 Request 和 Response类型的，所以，为了更清晰的表示出问题所在，需要对响应格式中的 Reason 与 Message 配置，这也就是我们在客户端看到的报错信息。
&metav1.Status{ Code: http.StatusForbidden, Reason: func() metav1.StatusReason { return metav1.StatusReasonForbidden }(), Message: fmt.Sprintf("the resource %s couldn't to allow entry.", deploy.Kind), } 通过上面的设置用户可以看到下列错误
$ kubectl apply -f nginx.yaml Error from server (Forbidden): error when creating "nginx.yaml": admission webhook "valipod-policy.example.com" denied the request: the resource Deployment couldn't to allow entry. 注：必须的参数还包含，UID，allowed，这两个是必须的，上面阐述的只是对用户友好的提示信息
下面的报错就是对相应格式设置错误
Error from server (InternalError): error when creating "nginx.yaml": Internal error occurred: failed calling webhook "pod-policy.example.com": the server rejected our request for an unknown reason 相应信息版本问题
相应信息也需要指定一个版本，这个与请求来的结构中拿即可
admissionResp.APIVersion = admission.APIVersion admissionResp.Kind = admission.Kind 下面是没有为对应相应信息配置对应KV的值出现的报错
Error from server (InternalError): error when creating "nginx.yaml": Internal error occurred: failed calling webhook "pod-policy.example.com": expected webhook response of admission.k8s.io/v1, Kind=AdmissionReview, got /, Kind= 关于patch
kubernetes中patch使用的是特定的规范，如 jsonpatch
kubernetes当前唯一支持的
patchType是JSONPatch。 有关更多详细信息，请参见 JSON patch对于
jsonpatch是一个固定的类型，在go中必须定义其结构体{ "op": "add", // 做什么操作 "path": "/spec/replicas", // 操作的路径 "value": 3 // 对应添加的key value }
下面就是字符串类型设置为布尔型产生的报错
Error from server (InternalError): error when creating "nginx.yaml": Internal error occurred: v1.Deployment.ObjectMeta: v1.ObjectMeta.Annotations: ReadString: expects " or n, but found t, error found in #10 byte of ...|t/Allow":true},"crea|..., bigger context ...|tadata":{"annotations":{"nginx-deployment/Allow":true},"creationTimestamp":null,"managedFields":[{"m|.. 准备证书
Ubuntu
touch ./demoCAindex.txt touch ./demoCA/serial touch ./demoCA/crlnumber echo 01 > ./demoCA/serial mkdir ./demoCA/newcerts openssl genrsa -out cakey.pem 2048 openssl req -new -x509 -key cakey.pem -out cacert.pem -days 3650 -subj "/CN=admission webhook ca" openssl genrsa -out tls.key 2048 openssl req -new -key tls.key -subj "/CN=admission webhook client" -reqexts webhook -config <(cat /etc/ssl/openssl.cnf <(printf "[webhook]nsubjectAltName=DNS: admission-webhook, DNS: admission-webhook.default.svc, DNS: admission-webhook.default.svc.cluster.local, IP:10.0.0.1, IP:10.0.0.4")) -out tls.csr sed -i 's/= match/= optional/g' /etc/ssl/openssl.cnf openssl ca -in tls.csr -cert cacert.pem -keyfile cakey.pem -out tls.crt -days 300 -extensions webhook -extfile <(cat /etc/ssl/openssl.cnf <(printf "[webhook]nsubjectAltName=DNS: admission-webhook, DNS: admission-webhook.default.svc, DNS: admission-webhook.default.svc.cluster.local, IP:10.0.0.1, IP:10.0.0.4")) CentOS
touch /etc/pki/CA/index.txt touch /etc/pki/CA/serial # 下一个要颁发的编号 16进制 touch /etc/pki/CA/crlnumber echo 01 > /etc/pki/CA/serial openssl req -new -x509 -key cakey.pem -out cacert.pem -days 3650 -subj "/CN=admission webhook ca" openssl genrsa -out tls.key 2048 openssl req -new -key tls.key -subj "/CN=admission webhook client" -reqexts webhook -config <(cat /etc/pki/tls/openssl.cnf <(printf "[webhook]nsubjectAltName=DNS: admission-webhook, DNS: admission-webhook.default.svc, DNS: admission-webhook.default.svc.cluster.local, IP:10.0.0.1, IP:10.0.0.4")) -out tls.csr sed -i 's/= match/= optional/g' /etc/ssl/openssl.cnf openssl ca -in tls.csr -cert cacert.pem -keyfile cakey.pem -out tls.crt -days 300 -extensions webhook -extfile <(cat /etc/pki/tls/openssl.cnf <(printf "[webhook]nsubjectAltName=DNS: admission-webhook, DNS: admission-webhook.default.svc, DNS: admission-webhook.default.svc.cluster.local, IP:10.0.0.1, IP:10.0.0.4")) 通过部署测试结果
可以看到我们自己注入的 annotation nginx-deployment/Allow: true，在该示例中，仅为演示过程，而不是真的策略，实际环境中可以根据情况进行定制自己的策略。
结果可以看出，当在 mutating 中不通过，即缺少对应的 annotation 标签 , 则 validating 会不允许准入
$ kubectl describe deploy nginx-deployment Name: nginx-deployment Namespace: default CreationTimestamp: Mon, 11 Jul 2022 20:25:16 +0800 Labels: <none> Annotations: deployment.kubernetes.io/revision: 1 nginx-deployment/Allow: true Selector: app=nginx Replicas: 1 desired | 1 updated | 1 total | 1 available | 0 unavailable StrategyType: RollingUpdate MinReadySeconds: 0 RollingUpdateStrategy: 25% max unavailable, 25% max surge Pod Template: Labels: app=nginx Containers: nginx: Image: nginx:1.14.2 Reference
extensible admission controllers
