我们已经知道，Service对集群之外暴露服务的主要方式有两种：NodePort和LoadBalancer，但是这两种方式，都有一定的缺点：
基于这种现状，Kubernetes提供了Ingress资源对象，Ingress只需要一个NodePort或者一个LB就可以满足暴露多个Service的需求。
客户端首先对 域名 执行 DNS 解析，得到 Ingress Controller 所在节点的 IP，然后客户端向 Ingress Controller 发送 HTTP 请求，然后根据 Ingress 对象里面的描述匹配域名，找到对应的 Service 对象，并获取关联的 Endpoints 列表，将客户端的请求转发给其中一个 Pod。
本文我们来使用client-go实现一个自定义控制器，通过判断service的Annotations属性是否包含ingress/http字段，如果包含则创建ingress，如果不包含则不创建。而且如果存在ingress则进行删除。
首先我们创建项目。
$ mkdir ingress-manager && cd ingress-manager$ go mod init ingress-manager# 由于控制器部分的内容比较多，将它们单独放到pkg目录下$ mkdir pkg# 最终项目目录结构如下.├── go.mod├── go.sum├── main.go└── pkg └── controller.go接着我们来实现controller部分：
package pkgimport ( "context" apiCoreV1 "k8s.io/api/core/v1" netV1 "k8s.io/api/networking/v1" "k8s.io/apimachinery/pkg/api/errors" metaV1 "k8s.io/apimachinery/pkg/apis/meta/v1" "k8s.io/apimachinery/pkg/util/runtime" "k8s.io/apimachinery/pkg/util/wait" informersCoreV1 "k8s.io/client-go/informers/core/v1" informersNetV1 "k8s.io/client-go/informers/networking/v1" "k8s.io/client-go/kubernetes" coreV1 "k8s.io/client-go/listers/core/v1" v1 "k8s.io/client-go/listers/networking/v1" "k8s.io/client-go/tools/cache" "k8s.io/client-go/util/workqueue" "reflect" "time")const ( workNum = 5 // 工作的节点数 maxRetry = 10 // 最大重试次数 )// 定义控制器type Controller struct { client kubernetes.Interface ingressLister v1.IngressLister serviceLister coreV1.ServiceLister queue workqueue.RateLimitingInterface}// 初始化控制器func NewController(client kubernetes.Interface, serviceInformer informersCoreV1.ServiceInformer, ingressInformer informersNetV1.IngressInformer) Controller { c := Controller{ client: client, ingressLister: ingressInformer.Lister(), serviceLister: serviceInformer.Lister(), queue: workqueue.NewNamedRateLimitingQueue(workqueue.DefaultControllerRateLimiter(), "ingressManager"), } // 添加事件处理函数 serviceInformer.Informer().AddEventHandler(cache.ResourceEventHandlerFuncs{ AddFunc: c.addService, UpdateFunc: c.updateService, }) ingressInformer.Informer().AddEventHandler(cache.ResourceEventHandlerFuncs{ DeleteFunc: c.deleteIngress, }) return c}// 入队func (c *Controller) enqueue(obj interface{}) { key, err := cache.MetaNamespaceKeyFunc(obj) if err != nil { runtime.HandleError(err) } c.queue.Add(key)}func (c *Controller) addService(obj interface{}) { c.enqueue(obj)}func (c *Controller) updateService(oldObj, newObj interface{}) { // todo 比较annotation // 这里只是比较了对象是否相同，如果相同，直接返回 if reflect.DeepEqual(oldObj, newObj) { return } c.enqueue(newObj)}func (c *Controller) deleteIngress(obj interface{}) { ingress := obj.(*netV1.Ingress) ownerReference := metaV1.GetControllerOf(ingress) if ownerReference == nil { return } // 判断是否为真的service if ownerReference.Kind != "Service" { return } c.queue.Add(ingress.Namespace + "/" + ingress.Name)}// 启动控制器，可以看到开了五个协程，真正干活的是workerfunc (c *Controller) Run(stopCh chan struct{}) { for i := 0; i < workNum; i++ { go wait.Until(c.worker, time.Minute, stopCh) } <-stopCh}func (c *Controller) worker() { for c.processNextItem() { }}// 业务真正处理的地方func (c *Controller) processNextItem() bool { // 获取key item, shutdown := c.queue.Get() if shutdown { return false } defer c.queue.Done(item) // 调用业务逻辑 err := c.syncService(item.(string)) if err != nil { // 对错误进行处理 c.handlerError(item.(string), err) return false } return true}func (c *Controller) syncService(item string) error { namespace, name, err := cache.SplitMetaNamespaceKey(item) if err != nil { return err } // 获取service service, err := c.serviceLister.Services(namespace).Get(name) if err != nil { if errors.IsNotFound(err) { return nil } return err } // 新增和删除 _, ok := service.GetAnnotations()["ingress/http"] ingress, err := c.ingressLister.Ingresses(namespace).Get(name) if err != nil && !errors.IsNotFound(err) { return err } if ok && errors.IsNotFound(err) { // 创建ingress ig := c.constructIngress(service) _, err := c.client.NetworkingV1().Ingresses(namespace).Create(context.TODO(), ig, metaV1.CreateOptions{}) if err != nil { return err } } else if !ok && ingress != nil { // 删除ingress err := c.client.NetworkingV1().Ingresses(namespace).Delete(context.TODO(), name, metaV1.DeleteOptions{}) if err != nil { return err } } return nil}func (c *Controller) handlerError(key string, err error) { // 如果出现错误，重新加入队列,最大处理10次 if c.queue.NumRequeues(key) <= maxRetry { c.queue.AddRateLimited(key) return } runtime.HandleError(err) c.queue.Forget(key)}func (c *Controller) constructIngress(service *apiCoreV1.Service) *netV1.Ingress { // 构造ingress pathType := netV1.PathTypePrefix ingress := netV1.Ingress{} ingress.ObjectMeta.OwnerReferences = []metaV1.OwnerReference{ *metaV1.NewControllerRef(service, apiCoreV1.SchemeGroupVersion.WithKind("Service")), } ingress.Namespace = service.Namespace ingress.Name = service.Name ingress.Spec = netV1.IngressSpec{ Rules: []netV1.IngressRule{ { Host: "example.com", IngressRuleValue: netV1.IngressRuleValue{ HTTP: &netV1.HTTPIngressRuleValue{ Paths: []netV1.HTTPIngressPath{ { Path: "/", PathType: &pathType, Backend: netV1.IngressBackend{ Service: &netV1.IngressServiceBackend{ Name: service.Name, Port: netV1.ServiceBackendPort{ Number: 80, }, }, }, }, }, }, }, }, }, } return &ingress}接下来我们来实现main:
package mainimport ( "ingress-manager/pkg" "k8s.io/client-go/informers" "k8s.io/client-go/kubernetes" "k8s.io/client-go/rest" "k8s.io/client-go/tools/clientcmd")func main() { // 获取config // 先尝试从集群外部获取，获取不到则从集群内部获取 var config, err = clientcmd.BuildConfigFromFlags("", clientcmd.RecommendedHomeFile) if err != nil { clusterConfig, err := rest.InClusterConfig() if err != nil { panic(err) } config = clusterConfig } // 通过config创建 clientSet clientSet, err := kubernetes.NewForConfig(config) if err != nil { panic(err) } // 通过 client 创建 informer,添加事件处理函数 factory := informers.NewSharedInformerFactory(clientSet, 0) serviceInformer := factory.Core().V1().Services() ingressInformer := factory.Networking().V1().Ingresses() newController := pkg.NewController(clientSet, serviceInformer, ingressInformer) // 启动 informer stopCh := make(chan struct{}) factory.Start(stopCh) factory.WaitForCacheSync(stopCh) newController.Run(stopCh)}首先创建deploy和service：
apiVersion: apps/v1kind: Deploymentmetadata: name: my-nginxspec: selector: matchLabels: app: my-nginx template: metadata: labels: app: my-nginx spec: containers: - name: my-nginx image: nginx:1.17.1 ports: - containerPort: 80---apiVersion: v1kind: Servicemetadata: name: my-nginx labels: app: my-nginxspec: ports: - port: 80 protocol: TCP name: http selector: app: my-nginx创建完成后进行查看：
$ kubectl get deploy,service,ingressNAME READY UP-TO-DATE AVAILABLE AGEdeployment.apps/my-nginx 1/1 1 1 7mNAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGEservice/kubernetes ClusterIP 10.96.0.1 <none> 443/TCP 78dservice/my-nginx ClusterIP 10.105.32.46 <none> 80/TCP 7m上面的命令我分别获取deploy,service,ingress,但是只获取到了deploy和service，这符合我们的预期。接着我们给service/m-nginx中的annotations添加ingress/http: nginx：
$ kubectl edit service/my-nginxapiVersion: v1kind: Servicemetadata: annotations: ingress/http: nginx kubectl.kubernetes.io/last-applied-configuration: | {"apiVersion":"v1","kind":"Service","metadata":{"annotations":{},"labels":{"app":"my-nginx"},"name":"my-nginx","namespace":"default"},"spec":{"ports":[{"name":"http","port":80,"protocol":"TCP"}],"selector":{"app":"my-nginx"}}} ...... service/my-nginx edited重新进行查看：
$ kubectl get deploy,service,ingressNAME READY UP-TO-DATE AVAILABLE AGEdeployment.apps/demo-deployment 1/1 1 1 41ddeployment.apps/my-nginx 1/1 1 1 11mNAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGEservice/kubernetes ClusterIP 10.96.0.1 <none> 443/TCP 78dservice/my-nginx ClusterIP 10.105.32.46 <none> 80/TCP 11mNAME CLASS HOSTS ADDRESS PORTS AGEingress.networking.k8s.io/my-nginx <none> example.com 80 19s接着我们再来测试下，将ingress/http: nginx注释掉，看看ingress是否会自动删除：
$ kubectl get deploy,service,ingressNAME READY UP-TO-DATE AVAILABLE AGEdeployment.apps/demo-deployment 1/1 1 1 41ddeployment.apps/my-nginx 1/1 1 1 19mNAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGEservice/kubernetes ClusterIP 10.96.0.1 <none> 443/TCP 78dservice/my-nginx ClusterIP 10.105.32.46 <none> 80/TCP 19m我们发现和我们预期的效果一样。
如果service被删除了，ingress肯定也是不会存在的。这个这里就不多演示了。有兴趣可以自行测试下。