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Kubernetes 能够应用一个 lock 对象,进行多实例的选举:
- 抢到 lock 对象更新权的实例即为 leader;
lock 对象能够是:
- Lease
- ConfigMap
- Endpoints
controller-runtime 罕用于 operator 的开发,其封装了 client-go 中 leader 选举的细节,leader 选举的场景为:
- 某一时刻只有一个实例能够 reconcile,其它实例处于 standby 状态;
- 一旦 leader 实例挂掉,standby 实例能够顶上,继续执行 reconcile;
一.operator
Operator 开发中,应用 controller-runtime 实现 leader 选举非常简单,调用时传入 election 参数即可:
func main() {flag.BoolVar(&enableLeaderElection, "enableLeaderElection", false, "default false, if enabled the cronHPA would be in primary and standby mode.")
flag.Parse()
mgr, err := ctrl.NewManager(ctrl.GetConfigOrDie(), ctrl.Options{
LeaderElection: enableLeaderElection,
LeaderElectionID: "kubernetes-cronhpa-controller",
MetricsBindAddress: metricsAddr,
})
...
}
多实例抢锁时,应用的资源对象为 configmap:
# kubectl get cm -n kube-system kubernetes-cronhpa-controller -oyaml
apiVersion: v1
kind: ConfigMap
metadata:
annotations:
control-plane.alpha.kubernetes.io/leader: '{"holderIdentity":"kubernetes-cronhpa-controller-6bcbdf9844-d2z4q_c36ac963-3e9c-4e32-ac14-ab48b6f2633b","leaseDurationSeconds":15,"acquireTime":"2023-04-08T16:14:30Z","renewTime":"2023-04-10T07:55:15Z","leaderTransitions":126}'
creationTimestamp: "2022-10-13T06:20:42Z"
managedFields:
- apiVersion: v1
fieldsType: FieldsV1
...
manager: kubernetes-cronhpa-controller
operation: Update
time: "2022-10-13T06:20:42Z"
name: kubernetes-cronhpa-controller
namespace: kube-system
resourceVersion: "76431408"
uid: 5099216c-2fd6-452a-afeb-bd39047c2cbb
二.controller-runtime
若应用底层的 client-go 进行实例选举,通常有以下步骤:
- 首先,创立 resourcelock,指定锁的资源类型;
- 而后,创立 leaderElector 对象,调用 leaderElector.Run();
controller-runtime 也是这么做的。
1. 创立 resourcelock
创立 ControllerManager 的时候,创立 resourcelock:
// controller-runtime/pkg/manager/manager.go
func New(config *rest.Config, options Options) (Manager, error) {
...
resourceLock, err := options.newResourceLock(leaderConfig, recorderProvider, leaderelection.Options{
LeaderElection: options.LeaderElection,
LeaderElectionID: options.LeaderElectionID,
LeaderElectionNamespace: options.LeaderElectionNamespace,
})
if err != nil {return nil, err}
return &controllerManager{
config: config,
...
resourceLock: resourceLock,
}
}
创立 resourcelock 的细节:
- 能够看出,这里创立的是 ConfigMap 类型的 resourcelock;
// controller-runtime/pkg/leaderelection/leader_election.go
func NewResourceLock(config *rest.Config, recorderProvider recorder.Provider, options Options) (resourcelock.Interface, error) {
...
return resourcelock.New(resourcelock.ConfigMapsResourceLock,
options.LeaderElectionNamespace,
options.LeaderElectionID,
client.CoreV1(),
client.CoordinationV1(),
resourcelock.ResourceLockConfig{
Identity: id,
EventRecorder: recorderProvider.GetEventRecorderFor(id),
})
}
2. 创立 LeaderElector 对象,调用 LeaderElector.Run():
首先,是 ControllerManager.Start():
// controller-manager/pkg/manager/internal.go
func (cm *controllerManager) Start(stop <-chan struct{}) (err error) {
...
go func() {
if cm.resourceLock != nil { // 须要选举
err := cm.startLeaderElection()
if err != nil {cm.errChan <- err}
} else { // 不须要选举
// Treat not having leader election enabled the same as being elected.
close(cm.elected)
go cm.startLeaderElectionRunnables()}
}()
select {
case <-stop:
// We are done
return nil
case err := <-cm.errChan:
// Error starting or running a runnable
return err
}
}
若须要选举:
- 创立 LeaderElector 对象;
- 调用 LeaderElector.Run();
- 选举胜利后,执行 startLeaderElectionRunnables(),这里的 runables 即是 Reconcile();
// controller-runtime/pkg/manager/internal.go
func (cm *controllerManager) startLeaderElection() (err error) {
...
l, err := leaderelection.NewLeaderElector(leaderelection.LeaderElectionConfig{
Lock: cm.resourceLock,
LeaseDuration: cm.leaseDuration,
RenewDeadline: cm.renewDeadline,
RetryPeriod: cm.retryPeriod,
Callbacks: leaderelection.LeaderCallbacks{OnStartedLeading: func(_ context.Context) {close(cm.elected)
cm.startLeaderElectionRunnables() // 选举胜利后,执行 Reconcile()
},
OnStoppedLeading: cm.onStoppedLeading,
},
})
...
// Start the leader elector process
go l.Run(ctx)
return nil
}
若不要选举,则间接执行 startLeaderElectionRunnables(),即执行 Reconcile()。
参考:
1.https://itnext.io/leader-election-in-kubernetes-using-client-…
正文完
发表至: kubernetes
2023-04-22