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一文读懂 SuperEdge 拓扑算法
前言
SuperEdge 介绍
SuperEdge 是基于原生 Kubernetes 的边缘容器管理系统。该系统把云原生能力扩展到边缘侧，很好的实现了云端对边缘端的管理和控制。同时 superedge 自研了 service group 实现了基于边缘计算的服务访问控制，极大简化了应用从云端部署到边缘端的过程。SuperEdge service group拓扑感知特性
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[1]
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/hostnamelabel 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/zonelabel 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/regionlabel 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。
# 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 VERSIO
Nnode0 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
}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}
}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
}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
}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
}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
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
}
}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
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,
}
}
}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。
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-apiserverapplication-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。
【参考资料】
[1] 拓扑感知特性:【 https://kubernetes.io/docs/concepts/services-networking/service-topology/】
[2] duyanghao kubernetes-reading-notes: 【https://github.com/duyanghao/kubernetes-reading-notes/blob/master/superedge/service-group/README.md】往期精选推荐