官方给出的这几个资源的关系图还是比较清晰的： 1.Service: 自动管理工作负载整个生命周期。负责创建route,configuration以及每个service更新的revision。通过Service可以指定路由流量使用最新的revision，还是固定的revision。 2.Route：负责映射网络端点到一个或多个revision。可以通过多种方式管理流量。包括灰度流量和重命名路由。 3.Configuration:负责保持deployment的期望状态，提供了代码和配置之间清晰的分离，并遵循应用开发的12要素。修改一次Configuration产生一个revision。 4.Revision：Revision资源是对工作负载进行的每个修改的代码和配置的时间点快照。Revision是不可变对象，可以长期保留。
我们开始运行官方hello-world示例，看看会发生什么事情：
apiVersion: serving.knative.dev/v1alpha1 kind: Service metadata: name: helloworld-go namespace: default spec: runLatest: // RunLatest defines a simple Service. It will automatically configure a route that keeps the latest ready revision from the supplied configuration running. configuration: revisionTemplate: spec: container: image: registry.cn-shanghai.aliyuncs.com/larus/helloworld-go env: - name: TARGET value: "Go Sample v1"查看 knative-ingressgateway：
kubectl get svc knative-ingressgateway -n istio-system查看服务访问：DOMAIN
kubectl get ksvc helloworld-go --output=custom-columns=NAME:.metadata.name,DOMAIN:.status.domain这里直接使用cluster ip即可访问
curl -H "Host: helloworld-go.default.example.com" http://10.96.199.35目前看一下服务是部署ok的。那我们看一下k8s里面创建了哪些资源：
我们可以发现通过Serving,在k8s中创建了2个service和1个deployment： 那么究竟Serving中做了哪些处理，接下来我们分析一下Serving源代码
先看一下各个组件的控制器启动代码，这个比较好找，在/cmd/controller/main.go中。 依次启动configuration、revision、route、labeler、service和clusteringress控制器。
... controllers := []*controller.Impl{ configuration.NewController( opt, configurationInformer, revisionInformer, ), revision.NewController( opt, revisionInformer, kpaInformer, imageInformer, deploymentInformer, coreServiceInformer, endpointsInformer, configMapInformer, buildInformerFactory, ), route.NewController( opt, routeInformer, configurationInformer, revisionInformer, coreServiceInformer, clusterIngressInformer, ), labeler.NewRouteToConfigurationController( opt, routeInformer, configurationInformer, revisionInformer, ), service.NewController( opt, serviceInformer, configurationInformer, routeInformer, ), clusteringress.NewController( opt, clusterIngressInformer, virtualServiceInformer, ), } ...首先我们要从Service来看，因为我们一开始的输入就是Service资源。在/pkg/reconciler/v1alpha1/service/service.go。 比较简单，就是根据Service创建Configuration和Route资源
func (c *Reconciler) reconcile(ctx context.Context, service *v1alpha1.Service) error { ... configName := resourcenames.Configuration(service) config, err := c.configurationLister.Configurations(service.Namespace).Get(configName) if errors.IsNotFound(err) { config, err = c.createConfiguration(service) ... routeName := resourcenames.Route(service) route, err := c.routeLister.Routes(service.Namespace).Get(routeName) if errors.IsNotFound(err) { route, err = c.createRoute(service) ... }/pkg/reconciler/v1alpha1/route/route.go 看一下Route中reconcile做了哪些处理： 1.判断是否有Ready的Revision可进行traffic 2.设置目标流量的Revision（runLatest:使用最新的版本;pinned：固定版本，不过已弃用;release:通过允许在两个修订版之间拆分流量，逐步扩大到新修订版，用于替换pinned。manual：手动模式，目前来看并未实现） 3.创建ClusterIngress:Route不直接依赖于VirtualService[https://istio.io/docs/reference/config/istio.networking.v1alpha3/#VirtualService] ,而是依赖一个中间资源ClusterIngress，它可以针对不同的网络平台进行不同的协调。目前实现是基于istio网络平台。 4.创建k8s service:这个Service主要为Istio路由提供域名访问。
func (c *Reconciler) reconcile(ctx context.Context, r *v1alpha1.Route) error { .... // 基于是否有Ready的Revision traffic, err := c.configureTraffic(ctx, r) if traffic == nil || err != nil { // Traffic targets aren't ready, no need to configure child resources. return err } logger.Info("Updating targeted revisions.") // In all cases we will add annotations to the referred targets. This is so that when they become // routable we can know (through a listener) and attempt traffic configuration again. if err := c.reconcileTargetRevisions(ctx, traffic, r); err != nil { return err } // Update the information that makes us Addressable. r.Status.Domain = routeDomain(ctx, r) r.Status.DeprecatedDomainInternal = resourcenames.K8sServiceFullname(r) r.Status.Address = &duckv1alpha1.Addressable{ Hostname: resourcenames.K8sServiceFullname(r), } // Add the finalizer before creating the ClusterIngress so that we can be sure it gets cleaned up. if err := c.ensureFinalizer(r); err != nil { return err } logger.Info("Creating ClusterIngress.") desired := resources.MakeClusterIngress(r, traffic, ingressClassForRoute(ctx, r)) clusterIngress, err := c.reconcileClusterIngress(ctx, r, desired) if err != nil { return err } r.Status.PropagateClusterIngressStatus(clusterIngress.Status) logger.Info("Creating/Updating placeholder k8s services") if err := c.reconcilePlaceholderService(ctx, r, clusterIngress); err != nil { return err } r.Status.ObservedGeneration = r.Generation logger.Info("Route successfully synced") return nil }看一下helloworld-go生成的Route资源文件：
apiVersion: serving.knative.dev/v1alpha1 kind: Route metadata: name: helloworld-go namespace: default ... spec: generation: 1 traffic: - configurationName: helloworld-go percent: 100 status: ... domain: helloworld-go.default.example.com domainInternal: helloworld-go.default.svc.cluster.local traffic: - percent: 100 # 所有的流量通过这个revision revisionName: helloworld-go-00001 # 使用helloworld-go-00001 revision这里可以看到通过helloworld-go配置, 找到了已经ready的helloworld-go-00001(Revision)。
/pkg/reconciler/v1alpha1/configuration/configuration.go 1.获取当前Configuration对应的Revision, 若不存在则创建。 2.为Configuration设置最新的Revision 3.根据Revision是否readiness，设置Configuration的状态LatestReadyRevisionName
func (c *Reconciler) reconcile(ctx context.Context, config *v1alpha1.Configuration) error { ... // First, fetch the revision that should exist for the current generation. lcr, err := c.latestCreatedRevision(config) if errors.IsNotFound(err) { lcr, err = c.createRevision(ctx, config) ... revName := lcr.Name // Second, set this to be the latest revision that we have created. config.Status.SetLatestCreatedRevisionName(revName) config.Status.ObservedGeneration = config.Generation // Last, determine whether we should set LatestReadyRevisionName to our // LatestCreatedRevision based on its readiness. rc := lcr.Status.GetCondition(v1alpha1.RevisionConditionReady) switch { case rc == nil || rc.Status == corev1.ConditionUnknown: logger.Infof("Revision %q of configuration %q is not ready", revName, config.Name) case rc.Status == corev1.ConditionTrue: logger.Infof("Revision %q of configuration %q is ready", revName, config.Name) created, ready := config.Status.LatestCreatedRevisionName, config.Status.LatestReadyRevisionName if ready == "" { // Surface an event for the first revision becoming ready. c.Recorder.Event(config, corev1.EventTypeNormal, "ConfigurationReady", "Configuration becomes ready") } // Update the LatestReadyRevisionName and surface an event for the transition. config.Status.SetLatestReadyRevisionName(lcr.Name) if created != ready { c.Recorder.Eventf(config, corev1.EventTypeNormal, "LatestReadyUpdate", "LatestReadyRevisionName updated to %q", lcr.Name) } ... }看一下helloworld-go生成的Configuration资源文件：
apiVersion: serving.knative.dev/v1alpha1 kind: Configuration metadata: name: helloworld-go namespace: default ... spec: generation: 1 revisionTemplate: metadata: creationTimestamp: null spec: container: env: - name: TARGET value: Go Sample v1 image: registry.cn-shanghai.aliyuncs.com/larus/helloworld-go name: "" resources: {} timeoutSeconds: 300 status: ... latestCreatedRevisionName: helloworld-go-00001 latestReadyRevisionName: helloworld-go-00001 observedGeneration: 1我们可以发现LatestReadyRevisionName设置了helloworld-go-00001(Revision)。
/pkg/reconciler/v1alpha1/revision/revision.go 1.获取build进度 2.设置镜像摘要 3.创建deployment 4.创建k8s service：根据Revision构建服务访问Service 5.创建fluentd configmap 6.创建KPA 感觉这段代码写的很优雅，函数执行过程写的很清晰，值得借鉴。另外我们也可以发现，目前knative只支持deployment的工作负载
func (c *Reconciler) reconcile(ctx context.Context, rev *v1alpha1.Revision) error { ... if err := c.reconcileBuild(ctx, rev); err != nil { return err } bc := rev.Status.GetCondition(v1alpha1.RevisionConditionBuildSucceeded) if bc == nil || bc.Status == corev1.ConditionTrue { // There is no build, or the build completed successfully. phases := []struct { name string f func(context.Context, *v1alpha1.Revision) error }{{ name: "image digest", f: c.reconcileDigest, }, { name: "user deployment", f: c.reconcileDeployment, }, { name: "user k8s service", f: c.reconcileService, }, { // Ensures our namespace has the configuration for the fluentd sidecar. name: "fluentd configmap", f: c.reconcileFluentdConfigMap, }, { name: "KPA", f: c.reconcileKPA, }} for _, phase := range phases { if err := phase.f(ctx, rev); err != nil { logger.Errorf("Failed to reconcile %s: %v", phase.name, zap.Error(err)) return err } } } ... }最后我们看一下生成的Revision资源：
apiVersion: serving.knative.dev/v1alpha1 kind: Service metadata: name: helloworld-go namespace: default ... spec: generation: 1 runLatest: configuration: revisionTemplate: spec: container: env: - name: TARGET value: Go Sample v1 image: registry.cn-shanghai.aliyuncs.com/larus/helloworld-go timeoutSeconds: 300 status: address: hostname: helloworld-go.default.svc.cluster.local ... domain: helloworld-go.default.example.com domainInternal: helloworld-go.default.svc.cluster.local latestCreatedRevisionName: helloworld-go-00001 latestReadyRevisionName: helloworld-go-00001 observedGeneration: 1 traffic: - percent: 100 revisionName: helloworld-go-00001这里我们可以看到访问域名helloworld-go.default.svc.cluster.local，以及当前revision的流量配比(100%)这样我们分析完之后，现在打开Serving这个黑盒：
这里只是基于简单的例子，分析了主要的业务流程处理代码。对于activator(如何唤醒业务容器)，autoscaler（Pod如何自动缩为0）等代码实现有兴趣的同学可以一起交流。
原文链接 本文为云栖社区原创内容，未经允许不得转载。
