深入Istio系列-Sidecar自动注入

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func NewWebhook(p WebhookParameters) (*Webhook, error) {
	if p.Mux == nil {
		return nil, errors.New("expected mux to be passed, but was not passed")
	}

	wh := &Webhook{
		watcher:    p.Watcher,
		meshConfig: p.Env.Mesh(),
		env:        p.Env,
		revision:   p.Revision,
	}

	p.Watcher.SetHandler(wh.updateConfig)
	sidecarConfig, valuesConfig, err := p.Watcher.Get()
	if err != nil {
		return nil, err
	}
	wh.updateConfig(sidecarConfig, valuesConfig)
    //初始化Webhook实例的时候注册/inject对应的处理器
	p.Mux.HandleFunc("/inject", wh.serveInject)
	p.Mux.HandleFunc("/inject/", wh.serveInject)

	p.Env.Watcher.AddMeshHandler(func() {
		wh.mu.Lock()
		wh.meshConfig = p.Env.Mesh()
		wh.mu.Unlock()
	})

	return wh, nil
}

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func (wh *Webhook) serveInject(w http.ResponseWriter, r *http.Request) {
	totalInjections.Increment()
	var body []byte
    // 获取请求体
	if r.Body != nil {
		if data, err := kube.HTTPConfigReader(r); err == nil {
			body = data
		} else {
			http.Error(w, err.Error(), http.StatusBadRequest)
			return
		}
	}
	if len(body) == 0 {
		handleError("no body found")
		http.Error(w, "no body found", http.StatusBadRequest)
		return
	}

	// verify the content type is accurate
	contentType := r.Header.Get("Content-Type")
	if contentType != "application/json" {
		handleError(fmt.Sprintf("contentType=%s, expect application/json", contentType))
		http.Error(w, "invalid Content-Type, want `application/json`", http.StatusUnsupportedMediaType)
		return
	}

	path := ""
	if r.URL != nil {
		path = r.URL.Path
	}

	var reviewResponse *kube.AdmissionResponse
	var obj runtime.Object
	var ar *kube.AdmissionReview
    // 解码请求体
	if out, _, err := deserializer.Decode(body, nil, obj); err != nil {
		handleError(fmt.Sprintf("Could not decode body: %v", err))
		reviewResponse = toAdmissionResponse(err)
	} else {
		log.Debugf("AdmissionRequest for path=%s\n", path)
		ar, err = kube.AdmissionReviewKubeToAdapter(out)
		if err != nil {
			handleError(fmt.Sprintf("Could not decode object: %v", err))
		}
        // 进入inject方法逻辑判断
		reviewResponse = wh.inject(ar, path)
	}

	response := kube.AdmissionReview{}
	response.Response = reviewResponse
	var responseKube runtime.Object
	var apiVersion string
	if ar != nil {
		apiVersion = ar.APIVersion
		response.TypeMeta = ar.TypeMeta
		if response.Response != nil {
			if ar.Request != nil {
				response.Response.UID = ar.Request.UID
			}
		}
	}
	responseKube = kube.AdmissionReviewAdapterToKube(&response, apiVersion)
	resp, err := json.Marshal(responseKube)
	if err != nil {
		log.Errorf("Could not encode response: %v", err)
		http.Error(w, fmt.Sprintf("could not encode response: %v", err), http.StatusInternalServerError)
	}
	if _, err := w.Write(resp); err != nil {
		log.Errorf("Could not write response: %v", err)
		http.Error(w, fmt.Sprintf("could not write response: %v", err), http.StatusInternalServerError)
	}
}

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func (wh *Webhook) inject(ar *kube.AdmissionReview, path string) *kube.AdmissionResponse {
	req := ar.Request
	var pod corev1.Pod
	if err := json.Unmarshal(req.Object.Raw, &pod); err != nil {
		handleError(fmt.Sprintf("Could not unmarshal raw object: %v %s", err,
			string(req.Object.Raw)))
		return toAdmissionResponse(err)
	}
	// Managed fields is sometimes extremely large, leading to excessive CPU time on patch generation
	// It does not impact the injection output at all, so we can just remove it.
	pod.ManagedFields = nil

	// Deal with potential empty fields, e.g., when the pod is created by a deployment
	podName := potentialPodName(pod.ObjectMeta)
	if pod.ObjectMeta.Namespace == "" {
		pod.ObjectMeta.Namespace = req.Namespace
	}
	log.Infof("Sidecar injection request for %v/%v", req.Namespace, podName)
	log.Debugf("Object: %v", string(req.Object.Raw))
	log.Debugf("OldObject: %v", string(req.OldObject.Raw))

	wh.mu.RLock()
	// Sicader注入判断逻辑
	if !injectRequired(IgnoredNamespaces.UnsortedList(), wh.Config, &pod.Spec, pod.ObjectMeta) {
		log.Infof("Skipping %s/%s due to policy check", pod.ObjectMeta.Namespace, podName)
		totalSkippedInjections.Increment()
		wh.mu.RUnlock()
		return &kube.AdmissionResponse{
			Allowed: true,
		}
	}

	proxyConfig := mesh.DefaultProxyConfig()
	if wh.env.PushContext != nil && wh.env.PushContext.ProxyConfigs != nil {
		if generatedProxyConfig := wh.env.PushContext.ProxyConfigs.EffectiveProxyConfig(
			&model.NodeMetadata{
				Namespace:   pod.Namespace,
				Labels:      pod.Labels,
				Annotations: pod.Annotations,
			}, wh.meshConfig); generatedProxyConfig != nil {
			proxyConfig = *generatedProxyConfig
		}
	}
	deploy, typeMeta := kube.GetDeployMetaFromPod(&pod)
	params := InjectionParameters{
		pod:                 &pod,
		deployMeta:          deploy,
		typeMeta:            typeMeta,
		templates:           wh.Config.Templates,
		defaultTemplate:     wh.Config.DefaultTemplates,
		aliases:             wh.Config.Aliases,
		meshConfig:          wh.meshConfig,
		proxyConfig:         &proxyConfig,
		valuesConfig:        wh.valuesConfig,
		revision:            wh.revision,
		injectedAnnotations: wh.Config.InjectedAnnotations,
		proxyEnvs:           parseInjectEnvs(path),
	}
	wh.mu.RUnlock()

	patchBytes, err := injectPod(params)
	if err != nil {
		handleError(fmt.Sprintf("Pod injection failed: %v", err))
		return toAdmissionResponse(err)
	}

	reviewResponse := kube.AdmissionResponse{
		Allowed: true,
		Patch:   patchBytes,
		PatchType: func() *string {
			pt := "JSONPatch"
			return &pt
		}(),
	}
	totalSuccessfulInjections.Increment()
	return &reviewResponse
}

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func injectRequired(ignored []string, config *Config, podSpec *corev1.PodSpec, metadata metav1.ObjectMeta) bool { // nolint: lll
	// Skip injection when host networking is enabled. The problem is
	// that the iptables changes are assumed to be within the pod when,
	// in fact, they are changing the routing at the host level. This
	// often results in routing failures within a node which can
	// affect the network provider within the cluster causing
	// additional pod failures.

    // 主机网络模式不注入sicader
	if podSpec.HostNetwork {
		return false
	}

	// skip special kubernetes system namespaces
    // kube-system、kube-public、kube-node-lease、local-path-storage四个名称空间不被注入sicader
	for _, namespace := range ignored {
		if metadata.Namespace == namespace {
			return false
		}
	}

	annos := metadata.GetAnnotations()

	var useDefault bool
	var inject bool
    // annotation 是否开启注入 `sidecar.istio.io/inject: "true"`
	objectSelector := annos[annotation.SidecarInject.Name]
	if lbl, labelPresent := metadata.GetLabels()[annotation.SidecarInject.Name]; labelPresent {
		// The label is the new API; if both are present we prefer the label
		objectSelector = lbl
	}
	switch strings.ToLower(objectSelector) {
	// http://yaml.org/type/bool.html
	case "y", "yes", "true", "on":
		inject = true
	case "":
		useDefault = true
	}

	// If an annotation is not explicitly given, check the LabelSelectors, starting with NeverInject
    // 判断 configmap `istio-sidecar-injector` NeverInject 匹配标签选择器
	if useDefault {
		for _, neverSelector := range config.NeverInjectSelector {
			selector, err := metav1.LabelSelectorAsSelector(&neverSelector)
			if err != nil {
				log.Warnf("Invalid selector for NeverInjectSelector: %v (%v)", neverSelector, err)
			} else if !selector.Empty() && selector.Matches(labels.Set(metadata.Labels)) {
				log.Debugf("Explicitly disabling injection for pod %s/%s due to pod labels matching NeverInjectSelector config map entry.",
					metadata.Namespace, potentialPodName(metadata))
				inject = false
				useDefault = false
				break
			}
		}
	}

	// If there's no annotation nor a NeverInjectSelector, check the AlwaysInject one
    //  判断 configmap `istio-sidecar-injector` AlwaysInject 匹配标签选择器
	if useDefault {
		for _, alwaysSelector := range config.AlwaysInjectSelector {
			selector, err := metav1.LabelSelectorAsSelector(&alwaysSelector)
			if err != nil {
				log.Warnf("Invalid selector for AlwaysInjectSelector: %v (%v)", alwaysSelector, err)
			} else if !selector.Empty() && selector.Matches(labels.Set(metadata.Labels)) {
				log.Debugf("Explicitly enabling injection for pod %s/%s due to pod labels matching AlwaysInjectSelector config map entry.",
					metadata.Namespace, potentialPodName(metadata))
				inject = true
				useDefault = false
				break
			}
		}
	}

	var required bool
    //   判断 configmap `istio-sidecar-injector`  默认策略policy
	switch config.Policy {
	default: // InjectionPolicyOff
		log.Errorf("Illegal value for autoInject:%s, must be one of [%s,%s]. Auto injection disabled!",
			config.Policy, InjectionPolicyDisabled, InjectionPolicyEnabled)
		required = false
	case InjectionPolicyDisabled:
		if useDefault {
			required = false
		} else {
			required = inject
		}
	case InjectionPolicyEnabled:
		if useDefault {
			required = true
		} else {
			required = inject
		}
	}

	if log.DebugEnabled() {
		// Build a log message for the annotations.
		annotationStr := ""
		for name := range AnnotationValidation {
			value, ok := annos[name]
			if !ok {
				value = "(unset)"
			}
			annotationStr += fmt.Sprintf("%s:%s ", name, value)
		}

		log.Debugf("Sidecar injection policy for %v/%v: namespacePolicy:%v useDefault:%v inject:%v required:%v %s",
			metadata.Namespace,
			potentialPodName(metadata),
			config.Policy,
			useDefault,
			inject,
			required,
			annotationStr)
	}

	return required
}