一文读懂SuperEdge拓扑算法

前言

SuperEdge service group 利用 application-grid-wrapper 实现拓扑感知，完成了同一个 nodeunit 内服务的闭环访问

在深入分析 application-grid-wrapper 之前，这里先简单介绍一下社区 Kubernetes 原生支持的拓扑感知特性

Kubernetes service topology awareness 特性于v1.17发布alpha版本，用于实现路由拓扑以及就近访问特性。用户需要在 service 中添加 topologyKeys 字段标示拓扑key类型，只有具有相同拓扑域的endpoint会被访问到，目前有三种 topologyKeys可供选择：

• "kubernetes.io/hostname"：访问本节点内(kubernetes.io/hostname label value相同)的 endpoint，如果没有则 service 访问失败
• "topology.kubernetes.io/zone"：访问相同zone域内(topology.kubernetes.io/zone label value 相同)的 endpoint，如果没有则 service 访问失败
• "topology.kubernetes.io/region"：访问相同region域内(topology.kubernetes.io/region label value相同)的 endpoint，如果没有则 service 访问失败

除了单独填写如上某一个拓扑key之外，还可以将这些key构造成列表进行填写，例如：["kubernetes.io/hostname", "topology.kubernetes.io/zone", "topology.kubernetes.io/region"]，这表示：优先访问本节点内的 endpoint；如果不存在，则访问同一个 zone 内的 endpoint；如果再不存在，则访问同一个 region 内的 endpoint，如果都不存在则访问失败

另外，还可以在列表最后(只能最后一项)添加"*"表示：如果前面拓扑域都失败，则访问任何有效的 endpoint，也即没有限制拓扑了，示例如下：

# A Service that prefers node local, zonal, then regional endpoints but falls back to cluster wide endpoints.
apiVersion: v1
kind: Service
metadata:
  name: my-service
spec:
  selector:
    app: my-app
  ports:
    - protocol: TCP
      port: 80
      targetPort: 9376
  topologyKeys:
    - "kubernetes.io/hostname"
    - "topology.kubernetes.io/zone"
    - "topology.kubernetes.io/region"
    - "*"

而service group实现的拓扑感知和社区对比，有如下区别：

• service group 拓扑key可以自定义，也即为 gridUniqKey，使用起来更加灵活；而社区实现目前只有三种选择："kubernetes.io/hostname"，"topology.kubernetes.io/zone" 以及 "topology.kubernetes.io/region"
• service group 只能填写一个拓扑 key，也即只能访问本拓扑域内有效的 endpoint，无法访问其它拓扑域的 endpoint；而社区可以通过 topologyKey 列表以及"*"实现其它备选拓扑域 endpoint 的访问

service group 实现的拓扑感知，service 配置如下：

# A Service that only prefers node zone1al endpoints.
apiVersion: v1
kind: Service
metadata:
  annotations:
    topologyKeys: '["zone1"]'
  labels:
    superedge.io/grid-selector: servicegrid-demo
  name: servicegrid-demo-svc
spec:
  ports:
  - port: 80
    protocol: TCP
    targetPort: 8080
  selector:
    appGrid: echo

在介绍完 service group 实现的拓扑感知后，我们深入到源码分析实现细节。同样的，这里以一个使用示例开始分析：

# step1: labels edge nodes
$ kubectl  get nodes
NAME    STATUS   ROLES    AGE   VERSION
node0   Ready    <none>   16d   v1.16.7
node1   Ready    <none>   16d   v1.16.7
node2   Ready    <none>   16d   v1.16.7
# nodeunit1(nodegroup and servicegroup zone1)
$ kubectl --kubeconfig config label nodes node0 zone1=nodeunit1  
# nodeunit2(nodegroup and servicegroup zone1)
$ kubectl --kubeconfig config label nodes node1 zone1=nodeunit2
$ kubectl --kubeconfig config label nodes node2 zone1=nodeunit2
...
# step3: deploy echo ServiceGrid
$ cat <<EOF | kubectl --kubeconfig config apply -f -
apiVersion: superedge.io/v1
kind: ServiceGrid
metadata:
  name: servicegrid-demo
  namespace: default
spec:
  gridUniqKey: zone1
  template:
    selector:
      appGrid: echo
    ports:
    - protocol: TCP
      port: 80
      targetPort: 8080
EOF
servicegrid.superedge.io/servicegrid-demo created
# note that there is only one relevant service generated
$ kubectl  get svc
NAME                   TYPE        CLUSTER-IP        EXTERNAL-IP   PORT(S)   AGE
kubernetes             ClusterIP   192.168.0.1       <none>        443/TCP   16d
servicegrid-demo-svc   ClusterIP   192.168.6.139     <none>        80/TCP    10m
# step4: access servicegrid-demo-svc(service topology and closed-looped)
# execute on node0
$ curl 192.168.6.139|grep "node name"
        node name:      node0
# execute on node1 and node2
$ curl 192.168.6.139|grep "node name"
        node name:      node2
$ curl 192.168.6.139|grep "node name"
        node name:      node1

在创建完 ServiceGrid CR 后，ServiceGrid Controller 负责根据 ServiceGrid 产生对应的 service (包含由serviceGrid.Spec.GridUniqKey 构成的 topologyKeys annotations)；而 application-grid-wrapper 根据 service 实现拓扑感知，下面依次分析。

ServiceGrid Controller 分析

ServiceGrid Controller 逻辑和 DeploymentGrid Controller 整体一致，如下：

• 1、创建并维护 service group 需要的若干CRDs(包括：ServiceGrid)
• 2、监听 ServiceGrid event，并填充 ServiceGrid 到工作队列中；循环从队列中取出 ServiceGrid 进行解析，创建并且维护对应的 service
• 3、监听 service event，并将相关的 ServiceGrid 塞到工作队列中进行上述处理，协助上述逻辑达到整体 reconcile 逻辑

注意这里区别于 DeploymentGrid Controller：

• 一个 ServiceGrid 对象只产生一个 service
• 只需额外监听 service event，无需监听 node 事件。因为 node的CRUD 与 ServiceGrid 无关
• ServiceGrid 对应产生的 service，命名为：{ServiceGrid}-svc

func (sgc *ServiceGridController) syncServiceGrid(key string) error {
    startTime := time.Now()
    klog.V(4).Infof("Started syncing service grid %q (%v)", key, startTime)
    defer func() {
        klog.V(4).Infof("Finished syncing service grid %q (%v)", key, time.Since(startTime))
    }()
    namespace, name, err := cache.SplitMetaNamespaceKey(key)
    if err != nil {
        return err
    }
    sg, err := sgc.svcGridLister.ServiceGrids(namespace).Get(name)
    if errors.IsNotFound(err) {
        klog.V(2).Infof("service grid %v has been deleted", key)
        return nil
    }
    if err != nil {
        return err
    }
    if sg.Spec.GridUniqKey == "" {
        sgc.eventRecorder.Eventf(sg, corev1.EventTypeWarning, "Empty", "This service grid has an empty grid key")
        return nil
    }
    // get service workload list of this grid
    svcList, err := sgc.getServiceForGrid(sg)
    if err != nil {
        return err
    }
    if sg.DeletionTimestamp != nil {
        return nil
    }
    // sync service grid relevant services workload
    return sgc.reconcile(sg, svcList)
}
func (sgc *ServiceGridController) getServiceForGrid(sg *crdv1.ServiceGrid) ([]*corev1.Service, error) {
    svcList, err := sgc.svcLister.Services(sg.Namespace).List(labels.Everything())
    if err != nil {
        return nil, err
    }
    labelSelector, err := common.GetDefaultSelector(sg.Name)
    if err != nil {
        return nil, err
    }
    canAdoptFunc := controller.RecheckDeletionTimestamp(func() (metav1.Object, error) {
        fresh, err := sgc.crdClient.SuperedgeV1().ServiceGrids(sg.Namespace).Get(context.TODO(), sg.Name, metav1.GetOptions{})
        if err != nil {
            return nil, err
        }
        if fresh.UID != sg.UID {
            return nil, fmt.Errorf("orignal service grid %v/%v is gone: got uid %v, wanted %v", sg.Namespace,
                sg.Name, fresh.UID, sg.UID)
        }
        return fresh, nil
    })
    cm := controller.NewServiceControllerRefManager(sgc.svcClient, sg, labelSelector, util.ControllerKind, canAdoptFunc)
    return cm.ClaimService(svcList)
}
func (sgc *ServiceGridController) reconcile(g *crdv1.ServiceGrid, svcList []*corev1.Service) error {
    var (
        adds    []*corev1.Service
        updates []*corev1.Service
        deletes []*corev1.Service
    )
    sgTargetSvcName := util.GetServiceName(g)
    isExistingSvc := false
    for _, svc := range svcList {
        if svc.Name == sgTargetSvcName {
            isExistingSvc = true
            template := util.KeepConsistence(g, svc)
            if !apiequality.Semantic.DeepEqual(template, svc) {
                updates = append(updates, template)
            }
        } else {
            deletes = append(deletes, svc)
        }
    }
    if !isExistingSvc {
        adds = append(adds, util.CreateService(g))
    }
    return sgc.syncService(adds, updates, deletes)
}
func CreateService(sg *crdv1.ServiceGrid) *corev1.Service {
    svc := &corev1.Service{
        ObjectMeta: metav1.ObjectMeta{
            Name:      GetServiceName(sg),
            Namespace: sg.Namespace,
            // Append existed ServiceGrid labels to service to be created
            Labels: func() map[string]string {
                if sg.Labels != nil {
                    newLabels := sg.Labels
                    newLabels[common.GridSelectorName] = sg.Name
                    newLabels[common.GridSelectorUniqKeyName] = sg.Spec.GridUniqKey
                    return newLabels
                } else {
                    return map[string]string{
                        common.GridSelectorName:        sg.Name,
                        common.GridSelectorUniqKeyName: sg.Spec.GridUniqKey,
                    }
                }
            }(),
            Annotations: make(map[string]string),
        },
        Spec: sg.Spec.Template,
    }
    keys := make([]string, 1)
    keys[0] = sg.Spec.GridUniqKey
    keyData, _ := json.Marshal(keys)
    svc.Annotations[common.TopologyAnnotationsKey] = string(keyData)
    return svc
}

由于逻辑与DeploymentGrid类似，这里不展开细节，重点关注 application-grid-wrapper 部分

application-grid-wrapper 分析

在 ServiceGrid Controller 创建完 service 之后，application-grid-wrapper 的作用就开始启动了：

apiVersion: v1
kind: Service
metadata:
  annotations:
    topologyKeys: '["zone1"]'
  creationTimestamp: "2021-03-03T07:33:30Z"
  labels:
    superedge.io/grid-selector: servicegrid-demo
  name: servicegrid-demo-svc
  namespace: default
  ownerReferences:
  - apiVersion: superedge.io/v1
    blockOwnerDeletion: true
    controller: true
    kind: ServiceGrid
    name: servicegrid-demo
    uid: 78c74d3c-72ac-4e68-8c79-f1396af5a581
  resourceVersion: "127987090"
  selfLink: /api/v1/namespaces/default/services/servicegrid-demo-svc
  uid: 8130ba7b-c27e-4c3a-8ceb-4f6dd0178dfc
spec:
  clusterIP: 192.168.161.1
  ports:
  - port: 80
    protocol: TCP
    targetPort: 8080
  selector:
    appGrid: echo
  sessionAffinity: None
  type: ClusterIP
status:
  loadBalancer: {}

为了实现 Kubernetes 零侵入，需要在 kube-proxy与apiserver 通信之间添加一层 wrapper，架构如下：

调用链路如下：

kube-proxy -> application-grid-wrapper -> lite-apiserver -> kube-apiserver

因此application-grid-wrapper会起服务，接受来自kube-proxy的请求，如下：

func (s *interceptorServer) Run(debug bool, bindAddress string, insecure bool, caFile, certFile, keyFile string) error {
    ...
    klog.Infof("Start to run interceptor server")
    /* filter
     */
    server := &http.Server{Addr: bindAddress, Handler: s.buildFilterChains(debug)}
    if insecure {
        return server.ListenAndServe()
    }
    ...
    server.TLSConfig = tlsConfig
    return server.ListenAndServeTLS("", "")
}
func (s *interceptorServer) buildFilterChains(debug bool) http.Handler {
    handler := http.Handler(http.NewServeMux())
    handler = s.interceptEndpointsRequest(handler)
    handler = s.interceptServiceRequest(handler)
    handler = s.interceptEventRequest(handler)
    handler = s.interceptNodeRequest(handler)
    handler = s.logger(handler)
    if debug {
        handler = s.debugger(handler)
    }
    return handler
}

这里会首先创建 interceptorServer，然后注册处理函数，由外到内依次如下：

• debug：接受 debug 请求，返回 wrapper pprof 运行信息

• logger：打印请求日志

• node：接受 kube-proxy node GET(/api/v1/nodes/{node}) 请求，并返回node信息

• event：接受 kube-proxy events POST (/events)请求，并将请求转发给 lite-apiserver

  func (s *interceptorServer) interceptEventRequest(handler http.Handler) http.Handler {
    return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
        if r.Method != http.MethodPost || !strings.HasSuffix(r.URL.Path, "/events") {
            handler.ServeHTTP(w, r)
            return
        }
        targetURL, _ := url.Parse(s.restConfig.Host)
        reverseProxy := httputil.NewSingleHostReverseProxy(targetURL)
        reverseProxy.Transport, _ = rest.TransportFor(s.restConfig)
        reverseProxy.ServeHTTP(w, r)
    })
  }
  

• service：接受 kube-proxy service List&Watch(/api/v1/services) 请求，并根据 storageCache 内容返回(GetServices)

• endpoint：接受 kube-proxy endpoint List&Watch(/api/v1/endpoints) 请求，并根据 storageCache内容返回 (GetEndpoints)

下面先重点分析 cache 部分的逻辑，然后再回过头来分析具体的 http handler List&Watch 处理逻辑

wrapper 为了实现拓扑感知，自己维护了一个 cache，包括：node，service，endpoint。可以看到在 setupInformers 中注册了这三类资源的处理函数：

type storageCache struct {
    // hostName is the nodeName of node which application-grid-wrapper deploys on
    hostName         string
    wrapperInCluster bool
    // mu lock protect the following map structure
    mu           sync.RWMutex
    servicesMap  map[types.NamespacedName]*serviceContainer
    endpointsMap map[types.NamespacedName]*endpointsContainer
    nodesMap     map[types.NamespacedName]*nodeContainer
    // service watch channel
    serviceChan chan<- watch.Event
    // endpoints watch channel
    endpointsChan chan<- watch.Event
}
...
func NewStorageCache(hostName string, wrapperInCluster bool, serviceNotifier, endpointsNotifier chan watch.Event) *storageCache {
    msc := &storageCache{
        hostName:         hostName,
        wrapperInCluster: wrapperInCluster,
        servicesMap:      make(map[types.NamespacedName]*serviceContainer),
        endpointsMap:     make(map[types.NamespacedName]*endpointsContainer),
        nodesMap:         make(map[types.NamespacedName]*nodeContainer),
        serviceChan:      serviceNotifier,
        endpointsChan:    endpointsNotifier,
    }
    return msc
}
...
func (s *interceptorServer) Run(debug bool, bindAddress string, insecure bool, caFile, certFile, keyFile string) error {
    ...
    if err := s.setupInformers(ctx.Done()); err != nil {
        return err
    }
    klog.Infof("Start to run interceptor server")
    /* filter
     */
    server := &http.Server{Addr: bindAddress, Handler: s.buildFilterChains(debug)}
    ...
    return server.ListenAndServeTLS("", "")
}
func (s *interceptorServer) setupInformers(stop <-chan struct{}) error {
    klog.Infof("Start to run service and endpoints informers")
    noProxyName, err := labels.NewRequirement(apis.LabelServiceProxyName, selection.DoesNotExist, nil)
    if err != nil {
        klog.Errorf("can't parse proxy label, %v", err)
        return err
    }
    noHeadlessEndpoints, err := labels.NewRequirement(v1.IsHeadlessService, selection.DoesNotExist, nil)
    if err != nil {
        klog.Errorf("can't parse headless label, %v", err)
        return err
    }
    labelSelector := labels.NewSelector()
    labelSelector = labelSelector.Add(*noProxyName, *noHeadlessEndpoints)
    resyncPeriod := time.Minute * 5
    client := kubernetes.NewForConfigOrDie(s.restConfig)
    nodeInformerFactory := informers.NewSharedInformerFactory(client, resyncPeriod)
    informerFactory := informers.NewSharedInformerFactoryWithOptions(client, resyncPeriod,
        informers.WithTweakListOptions(func(options *metav1.ListOptions) {
            options.LabelSelector = labelSelector.String()
        }))
    nodeInformer := nodeInformerFactory.Core().V1().Nodes().Informer()
    serviceInformer := informerFactory.Core().V1().Services().Informer()
    endpointsInformer := informerFactory.Core().V1().Endpoints().Informer()
    /*
     */
    nodeInformer.AddEventHandlerWithResyncPeriod(s.cache.NodeEventHandler(), resyncPeriod)
    serviceInformer.AddEventHandlerWithResyncPeriod(s.cache.ServiceEventHandler(), resyncPeriod)
    endpointsInformer.AddEventHandlerWithResyncPeriod(s.cache.EndpointsEventHandler(), resyncPeriod)
    go nodeInformer.Run(stop)
    go serviceInformer.Run(stop)
    go endpointsInformer.Run(stop)
    if !cache.WaitForNamedCacheSync("node", stop,
        nodeInformer.HasSynced,
        serviceInformer.HasSynced,
        endpointsInformer.HasSynced) {
        return fmt.Errorf("can't sync informers")
    }
    return nil
}
func (sc *storageCache) NodeEventHandler() cache.ResourceEventHandler {
    return &nodeHandler{cache: sc}
}
func (sc *storageCache) ServiceEventHandler() cache.ResourceEventHandler {
    return &serviceHandler{cache: sc}
}
func (sc *storageCache) EndpointsEventHandler() cache.ResourceEventHandler {
    return &endpointsHandler{cache: sc}
}

这里依次分析 NodeEventHandler，ServiceEventHandler 以及 EndpointsEventHandler，如下：

1、NodeEventHandler

NodeEventHandler 负责监听 node 资源相关 event，并将 node 以及 node Labels 添加到storageCache.nodesMap 中 (key 为 nodeName，value 为 node 以及 node labels)

func (nh *nodeHandler) add(node *v1.Node) {
    sc := nh.cache
    sc.mu.Lock()
    nodeKey := types.NamespacedName{Namespace: node.Namespace, Name: node.Name}
    klog.Infof("Adding node %v", nodeKey)
    sc.nodesMap[nodeKey] = &nodeContainer{
        node:   node,
        labels: node.Labels,
    }
    // update endpoints
    changedEps := sc.rebuildEndpointsMap()
    sc.mu.Unlock()
    for _, eps := range changedEps {
        sc.endpointsChan <- eps
    }
}
func (nh *nodeHandler) update(node *v1.Node) {
    sc := nh.cache
    sc.mu.Lock()
    nodeKey := types.NamespacedName{Namespace: node.Namespace, Name: node.Name}
    klog.Infof("Updating node %v", nodeKey)
    nodeContainer, found := sc.nodesMap[nodeKey]
    if !found {
        sc.mu.Unlock()
        klog.Errorf("Updating non-existed node %v", nodeKey)
        return
    }
    nodeContainer.node = node
    // return directly when labels of node stay unchanged
    if reflect.DeepEqual(node.Labels, nodeContainer.labels) {
        sc.mu.Unlock()
        return
    }
    nodeContainer.labels = node.Labels
    // update endpoints
    changedEps := sc.rebuildEndpointsMap()
    sc.mu.Unlock()
    for _, eps := range changedEps {
        sc.endpointsChan <- eps
    }
}
...

同时由于 node 的改变会影响 endpoint，因此会调用 rebuildEndpointsMap 刷新 storageCache.endpointsMap

// rebuildEndpointsMap updates all endpoints stored in storageCache.endpointsMap dynamically and constructs relevant modified events
func (sc *storageCache) rebuildEndpointsMap() []watch.Event {
    evts := make([]watch.Event, 0)
    for name, endpointsContainer := range sc.endpointsMap {
        newEps := pruneEndpoints(sc.hostName, sc.nodesMap, sc.servicesMap, endpointsContainer.endpoints, sc.wrapperInCluster)
        if apiequality.Semantic.DeepEqual(newEps, endpointsContainer.modified) {
            continue
        }
        sc.endpointsMap[name].modified = newEps
        evts = append(evts, watch.Event{
            Type:   watch.Modified,
            Object: newEps,
        })
    }
    return evts
}

rebuildEndpointsMap 是 cache 的核心函数，同时也是拓扑感知的算法实现：

// pruneEndpoints filters endpoints using serviceTopology rules combined by services topologyKeys and node labels
func pruneEndpoints(hostName string,
    nodes map[types.NamespacedName]*nodeContainer,
    services map[types.NamespacedName]*serviceContainer,
    eps *v1.Endpoints, wrapperInCluster bool) *v1.Endpoints {
    epsKey := types.NamespacedName{Namespace: eps.Namespace, Name: eps.Name}
    if wrapperInCluster {
        eps = genLocalEndpoints(eps)
    }
    // dangling endpoints
    svc, ok := services[epsKey]
    if !ok {
        klog.V(4).Infof("Dangling endpoints %s, %+#v", eps.Name, eps.Subsets)
        return eps
    }
    // normal service
    if len(svc.keys) == 0 {
        klog.V(4).Infof("Normal endpoints %s, %+#v", eps.Name, eps.Subsets)
        return eps
    }
    // topology endpoints
    newEps := eps.DeepCopy()
    for si := range newEps.Subsets {
        subnet := &newEps.Subsets[si]
        subnet.Addresses = filterConcernedAddresses(svc.keys, hostName, nodes, subnet.Addresses)
        subnet.NotReadyAddresses = filterConcernedAddresses(svc.keys, hostName, nodes, subnet.NotReadyAddresses)
    }
    klog.V(4).Infof("Topology endpoints %s: subnets from %+#v to %+#v", eps.Name, eps.Subsets, newEps.Subsets)
    return newEps
}
// filterConcernedAddresses aims to filter out endpoints addresses within the same node unit
func filterConcernedAddresses(topologyKeys []string, hostName string, nodes map[types.NamespacedName]*nodeContainer,
    addresses []v1.EndpointAddress) []v1.EndpointAddress {
    hostNode, found := nodes[types.NamespacedName{Name: hostName}]
    if !found {
        return nil
    }
    filteredEndpointAddresses := make([]v1.EndpointAddress, 0)
    for i := range addresses {
        addr := addresses[i]
        if nodeName := addr.NodeName; nodeName != nil {
            epsNode, found := nodes[types.NamespacedName{Name: *nodeName}]
            if !found {
                continue
            }
            if hasIntersectionLabel(topologyKeys, hostNode.labels, epsNode.labels) {
                filteredEndpointAddresses = append(filteredEndpointAddresses, addr)
            }
        }
    }
    return filteredEndpointAddresses
}
func hasIntersectionLabel(keys []string, n1, n2 map[string]string) bool {
    if n1 == nil || n2 == nil {
        return false
    }
    for _, key := range keys {
        val1, v1found := n1[key]
        val2, v2found := n2[key]
        if v1found && v2found && val1 == val2 {
            return true
        }
    }
    return false
}

算法逻辑如下：

• 判断 endpoint 是否为 default kubernetes service，如果是，则将该 endpoint 转化为 wrapper 所在边缘节点的 lite-apiserver 地址(127.0.0.1)和端口(51003)

apiVersion: v1
kind: Endpoints
metadata:
  annotations:
    superedge.io/local-endpoint: 127.0.0.1
    superedge.io/local-port: "51003"
  name: kubernetes
  namespace: default
subsets:
- addresses:
  - ip: 172.31.0.60
  ports:
  - name: https
    port: xxx
    protocol: TCP

func genLocalEndpoints(eps *v1.Endpoints) *v1.Endpoints {
    if eps.Namespace != metav1.NamespaceDefault || eps.Name != MasterEndpointName {
        return eps
    }
    klog.V(4).Infof("begin to gen local ep %v", eps)
    ipAddress, e := eps.Annotations[EdgeLocalEndpoint]
    if !e {
        return eps
    }
    portStr, e := eps.Annotations[EdgeLocalPort]
    if !e {
        return eps
    }
    klog.V(4).Infof("get local endpoint %s:%s", ipAddress, portStr)
    port, err := strconv.ParseInt(portStr, 10, 32)
    if err != nil {
        klog.Errorf("parse int %s err %v", portStr, err)
        return eps
    }
    ip := net.ParseIP(ipAddress)
    if ip == nil {
        klog.Warningf("parse ip %s nil", ipAddress)
        return eps
    }
    nep := eps.DeepCopy()
    nep.Subsets = []v1.EndpointSubset{
        {
            Addresses: []v1.EndpointAddress{
                {
                    IP: ipAddress,
                },
            },
            Ports: []v1.EndpointPort{
                {
                    Protocol: v1.ProtocolTCP,
                    Port:     int32(port),
                    Name:     "https",
                },
            },
        },
    }
    klog.V(4).Infof("gen new endpoint complete %v", nep)
    return nep
}

这样做的目的是使边缘节点上的服务采用集群内 (InCluster) 方式访问的 apiserver 为本地的 lite-apiserver，而不是云端的 apiserver

• 从 storageCache.servicesMap cache 中根据 endpoint 名称 (namespace/name) 取出对应 service，如果该 service 没有 topologyKeys 则无需做拓扑转化 (非service group)

func getTopologyKeys(objectMeta *metav1.ObjectMeta) []string {
    if !hasTopologyKey(objectMeta) {
        return nil
    }
    var keys []string
    keyData := objectMeta.Annotations[TopologyAnnotationsKey]
    if err := json.Unmarshal([]byte(keyData), &keys); err != nil {
        klog.Errorf("can't parse topology keys %s, %v", keyData, err)
        return nil
    }
    return keys
}

• 调用 filterConcernedAddresses 过滤 endpoint.Subsets Addresses 以及 NotReadyAddresses，只保留同一个 service topologyKeys 中的 endpoint

// filterConcernedAddresses aims to filter out endpoints addresses within the same node unit
func filterConcernedAddresses(topologyKeys []string, hostName string, nodes map[types.NamespacedName]*nodeContainer,
    addresses []v1.EndpointAddress) []v1.EndpointAddress {
    hostNode, found := nodes[types.NamespacedName{Name: hostName}]
    if !found {
        return nil
    }
    filteredEndpointAddresses := make([]v1.EndpointAddress, 0)
    for i := range addresses {
        addr := addresses[i]
        if nodeName := addr.NodeName; nodeName != nil {
            epsNode, found := nodes[types.NamespacedName{Name: *nodeName}]
            if !found {
                continue
            }
            if hasIntersectionLabel(topologyKeys, hostNode.labels, epsNode.labels) {
                filteredEndpointAddresses = append(filteredEndpointAddresses, addr)
            }
        }
    }
    return filteredEndpointAddresses
}
func hasIntersectionLabel(keys []string, n1, n2 map[string]string) bool {
    if n1 == nil || n2 == nil {
        return false
    }
    for _, key := range keys {
        val1, v1found := n1[key]
        val2, v2found := n2[key]
        if v1found && v2found && val1 == val2 {
            return true
        }
    }
    return false
}

注意：如果 wrapper 所在边缘节点没有 service topologyKeys 标签，则也无法访问该 service

回到 rebuildEndpointsMap，在调用 pruneEndpoints 刷新了同一个拓扑域内的 endpoint 后，会将修改后的 endpoints 赋值给 storageCache.endpointsMap [endpoint]. modified (该字段记录了拓扑感知后修改的endpoints)。

func (nh *nodeHandler) add(node *v1.Node) {
    sc := nh.cache
    sc.mu.Lock()
    nodeKey := types.NamespacedName{Namespace: node.Namespace, Name: node.Name}
    klog.Infof("Adding node %v", nodeKey)
    sc.nodesMap[nodeKey] = &nodeContainer{
        node:   node,
        labels: node.Labels,
    }
    // update endpoints
    changedEps := sc.rebuildEndpointsMap()
    sc.mu.Unlock()
    for _, eps := range changedEps {
        sc.endpointsChan <- eps
    }
}
// rebuildEndpointsMap updates all endpoints stored in storageCache.endpointsMap dynamically and constructs relevant modified events
func (sc *storageCache) rebuildEndpointsMap() []watch.Event {
    evts := make([]watch.Event, 0)
    for name, endpointsContainer := range sc.endpointsMap {
        newEps := pruneEndpoints(sc.hostName, sc.nodesMap, sc.servicesMap, endpointsContainer.endpoints, sc.wrapperInCluster)
        if apiequality.Semantic.DeepEqual(newEps, endpointsContainer.modified) {
            continue
        }
        sc.endpointsMap[name].modified = newEps
        evts = append(evts, watch.Event{
            Type:   watch.Modified,
            Object: newEps,
        })
    }
    return evts
}

另外，如果 endpoints (拓扑感知后修改的 endpoints) 发生改变，会构建 watch event，传递给 endpoints handler (interceptEndpointsRequest) 处理

2、ServiceEventHandler

storageCache.servicesMap 结构体 key 为 service 名称 (namespace/name)，value 为 serviceContainer，包含如下数据：

• svc：service对象
• keys：service topologyKeys

对于 service 资源的改动，这里用 Update event 说明：

func (sh *serviceHandler) update(service *v1.Service) {
    sc := sh.cache
    sc.mu.Lock()
    serviceKey := types.NamespacedName{Namespace: service.Namespace, Name: service.Name}
    klog.Infof("Updating service %v", serviceKey)
    newTopologyKeys := getTopologyKeys(&service.ObjectMeta)
    serviceContainer, found := sc.servicesMap[serviceKey]
    if !found {
        sc.mu.Unlock()
        klog.Errorf("update non-existed service, %v", serviceKey)
        return
    }
    sc.serviceChan <- watch.Event{
        Type:   watch.Modified,
        Object: service,
    }
    serviceContainer.svc = service
    // return directly when topologyKeys of service stay unchanged
    if reflect.DeepEqual(serviceContainer.keys, newTopologyKeys) {
        sc.mu.Unlock()
        return
    }
    serviceContainer.keys = newTopologyKeys
    // update endpoints
    changedEps := sc.rebuildEndpointsMap()
    sc.mu.Unlock()
    for _, eps := range changedEps {
        sc.endpointsChan <- eps
    }
}

逻辑如下：

• 获取 service topologyKeys
• 构建 service event.Modified event
• 比较 service topologyKeys 与已经存在的是否有差异
• 如果有差异则更新 topologyKeys，且调用 rebuildEndpointsMap刷新该 service 对应的 endpoints，如果 endpoints 发生变化，则构建 endpoints watch event，传递给 endpoints handler (interceptEndpointsRequest) 处理

3、EndpointsEventHandler

storageCache.endpointsMap 结构体 key 为 endpoints 名称(namespace/name)，value 为 endpointsContainer，包含如下数据：

• endpoints：拓扑修改前的 endpoints
• modified：拓扑修改后的 endpoints

对于 endpoints 资源的改动，这里用 Update event 说明：

func (eh *endpointsHandler) update(endpoints *v1.Endpoints) {
    sc := eh.cache
    sc.mu.Lock()
    endpointsKey := types.NamespacedName{Namespace: endpoints.Namespace, Name: endpoints.Name}
    klog.Infof("Updating endpoints %v", endpointsKey)
    endpointsContainer, found := sc.endpointsMap[endpointsKey]
    if !found {
        sc.mu.Unlock()
        klog.Errorf("Updating non-existed endpoints %v", endpointsKey)
        return
    }
    endpointsContainer.endpoints = endpoints
    newEps := pruneEndpoints(sc.hostName, sc.nodesMap, sc.servicesMap, endpoints, sc.wrapperInCluster)
    changed := !apiequality.Semantic.DeepEqual(endpointsContainer.modified, newEps)
    if changed {
        endpointsContainer.modified = newEps
    }
    sc.mu.Unlock()
    if changed {
        sc.endpointsChan <- watch.Event{
            Type:   watch.Modified,
            Object: newEps,
        }
    }
}

逻辑如下：

• 更新 endpointsContainer.endpoint 为新的 endpoints 对象
• 调用 pruneEndpoints 获取拓扑刷新后的 endpoints
• 比较 endpointsContainer.modified 与新刷新后的 endpoints
• 如果有差异则更新 endpointsContainer.modified，则构建 endpoints watch event，传递给 endpoints handler (interceptEndpointsRequest) 处理

在分析完NodeEventHandler，ServiceEventHandler以及EndpointsEventHandler之后，我们回到具体的http handler List&Watch处理逻辑上，这里以endpoints为例：

func (s *interceptorServer) interceptEndpointsRequest(handler http.Handler) http.Handler {
    return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
        if r.Method != http.MethodGet || !strings.HasPrefix(r.URL.Path, "/api/v1/endpoints") {
            handler.ServeHTTP(w, r)
            return
        }
        queries := r.URL.Query()
        acceptType := r.Header.Get("Accept")
        info, found := s.parseAccept(acceptType, s.mediaSerializer)
        if !found {
            klog.Errorf("can't find %s serializer", acceptType)
            w.WriteHeader(http.StatusBadRequest)
            return
        }
        encoder := scheme.Codecs.EncoderForVersion(info.Serializer, v1.SchemeGroupVersion)
        // list request
        if queries.Get("watch") == "" {
            w.Header().Set("Content-Type", info.MediaType)
            allEndpoints := s.cache.GetEndpoints()
            epsItems := make([]v1.Endpoints, 0, len(allEndpoints))
            for _, eps := range allEndpoints {
                epsItems = append(epsItems, *eps)
            }
            epsList := &v1.EndpointsList{
                Items: epsItems,
            }
            err := encoder.Encode(epsList, w)
            if err != nil {
                klog.Errorf("can't marshal endpoints list, %v", err)
                w.WriteHeader(http.StatusInternalServerError)
                return
            }
            return
        }
        // watch request
        timeoutSecondsStr := r.URL.Query().Get("timeoutSeconds")
        timeout := time.Minute
        if timeoutSecondsStr != "" {
            timeout, _ = time.ParseDuration(fmt.Sprintf("%ss", timeoutSecondsStr))
        }
        timer := time.NewTimer(timeout)
        defer timer.Stop()
        flusher, ok := w.(http.Flusher)
        if !ok {
            klog.Errorf("unable to start watch - can't get http.Flusher: %#v", w)
            w.WriteHeader(http.StatusMethodNotAllowed)
            return
        }
        e := restclientwatch.NewEncoder(
            streaming.NewEncoder(info.StreamSerializer.Framer.NewFrameWriter(w),
                scheme.Codecs.EncoderForVersion(info.StreamSerializer, v1.SchemeGroupVersion)),
            encoder)
        if info.MediaType == runtime.ContentTypeProtobuf {
            w.Header().Set("Content-Type", runtime.ContentTypeProtobuf+";stream=watch")
        } else {
            w.Header().Set("Content-Type", runtime.ContentTypeJSON)
        }
        w.Header().Set("Transfer-Encoding", "chunked")
        w.WriteHeader(http.StatusOK)
        flusher.Flush()
        for {
            select {
            case <-r.Context().Done():
                return
            case <-timer.C:
                return
            case evt := <-s.endpointsWatchCh:
                klog.V(4).Infof("Send endpoint watch event: %+#v", evt)
                err := e.Encode(&evt)
                if err != nil {
                    klog.Errorf("can't encode watch event, %v", err)
                    return
                }
                if len(s.endpointsWatchCh) == 0 {
                    flusher.Flush()
                }
            }
        }
    })
}

逻辑如下：

• 如果为List请求，则调用 GetEndpoints 获取拓扑修改后的 endpoints 列表，并返回

func (sc *storageCache) GetEndpoints() []*v1.Endpoints {
    sc.mu.RLock()
    defer sc.mu.RUnlock()
    epList := make([]*v1.Endpoints, 0, len(sc.endpointsMap))
    for _, v := range sc.endpointsMap {
        epList = append(epList, v.modified)
    }
    return epList
}

• 如果为 Watch 请求，则不断从 storageCache.endpointsWatchCh 管道中接受 watch event，并返回

interceptServiceRequest 逻辑与 interceptEndpointsRequest 一致，这里不再赘述。

总结

• SuperEdge service group 利用 application-grid-wrapper 实现拓扑感知，完成了同一个 nodeunit 内服务的闭环访问
• service group 实现的拓扑感知和 Kubernetes 社区原生实现对比，有如下区别：
  • service group 拓扑 key 可以自定义，也即为 gridUniqKey，使用起来更加灵活；而社区实现目前只有三种选择："kubernetes.io/hostname"，"topology.kubernetes.io/zone"以及"topology.kubernetes.io/region"
  • service group 只能填写一个拓扑 key，也即只能访问本拓扑域内有效的 endpoint，无法访问其它拓扑域的 endpoint；而社区可以通过 topologyKey 列表以及"*"实现其它备选拓扑域 endpoint 的访问
• ServiceGrid Controller 负责根据 ServiceGrid 产生对应的 service(包含由serviceGrid.Spec.GridUniqKey构成的 topologyKeys annotations)，逻辑和 DeploymentGrid Controller 整体一致，如下：
  • 创建并维护 service group 需要的若干 CRDs (包括：ServiceGrid)
  • 监听 ServiceGrid event，并填充 ServiceGrid 到工作队列中；循环从队列中取出ServiceGrid进行解析，创建并且维护对应的 service
  • 监听 service event，并将相关的 ServiceGrid 塞到工作队列中进行上述处理，协助上述逻辑达到整体 reconcile 逻辑
• 为了实现Kubernetes零侵入，需要在 kube-proxy 与 apiserver 通信之间添加一层 wrapper，调用链路如下：kube-proxy -> application-grid-wrapper -> lite-apiserver -> kube-apiserver
• application-grid-wrapper 是一个 http server，接受来自 kube-proxy 的请求，同时维护一个资源缓存，处理函数由外到内依次如下：
  • debug：接受 debug 请求，返回 wrapper pprof 运行信息
  • logger：打印请求日志
  • node：接受kube-proxy node GET (/api/v1/nodes/{node}) 请求，并返回 node 信息
  • event：接受 kube-proxy events POST (/events) 请求，并将请求转发给 lite-apiserver
  • service：接受 kube-proxy service List&Watch (/api/v1/services) 请求，并根据 storageCache 内容返回 (GetServices)。
  • endpoint：接受 kube-proxy endpoint List&Watch(/api/v1/endpoints) 请求，并根据storageCache 内容返回 (GetEndpoints)。
• wrapper 为了实现拓扑感知，维护了一个资源cache，包括：node，service，endpoint，同时注册了相关 event 处理函数。核心拓扑算法逻辑为：调用 filterConcernedAddresses 过滤 endpoint.Subsets Addresses 以及 NotReadyAddresses，只保留同一个 service topologyKeys 中的 endpoint。另外，如果 wrapper 所在边缘节点没有 service topologyKeys 标签，则也无法访问该 service。
• wrapper 接受来自 kube-proxy 对 endpoints 以及 service 的 List&Watch 请求，以 endpoints 为例：如果为List请求，则调用 GetEndpoints 获取拓扑修改后的 endpoints 列表，并返回；如果为 Watch 请求，则不断从 storageCache.endpointsWatchCh 管道中接受 watch event，并返回。service逻辑与 endpoints 一致。

展望

目前 SuperEdge service group 实现的拓扑算法功能更加灵活方便，如何处理与 Kubernetes 社区 service topology awareness 之间的关系值得探索，建议将 SuperEdge 拓扑算法推到社区

Refs

• duyanghao kubernetes-reading-notes