main.go

/*
Copyright 2019 The Caicloud Authors.

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/

package main

import (
	"context"
	"flag"
	"fmt"
	"net/http"
	"os"
	"os/signal"
	"syscall"
	"time"

	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
	"k8s.io/apiserver/pkg/server/healthz"
	clientset "k8s.io/client-go/kubernetes"
	"k8s.io/client-go/rest"
	"k8s.io/client-go/tools/clientcmd"
	"k8s.io/client-go/tools/leaderelection"
	"k8s.io/client-go/tools/leaderelection/resourcelock"
	"k8s.io/klog"
)

func buildConfig(kubeconfig string) (*rest.Config, error) {
	if kubeconfig != "" {
		cfg, err := clientcmd.BuildConfigFromFlags("", kubeconfig)
		if err != nil {
			return nil, err
		}
		return cfg, nil
	}

	cfg, err := rest.InClusterConfig()
	if err != nil {
		return nil, err
	}
	return cfg, nil
}

func main() {
	klog.InitFlags(nil)

	var port int
	var kubeconfig string
	var leaseLockName string
	var leaseLockNamespace string
	var id string

	flag.IntVar(&port, "port", 8080, "port to listen")
	flag.StringVar(&kubeconfig, "kubeconfig", "", "absolute path to the kubeconfig file")
	flag.StringVar(&id, "id", "", "the holder identity name")
	flag.StringVar(&leaseLockName, "lease-lock-name", "", "the lease lock resource name")
	flag.StringVar(&leaseLockNamespace, "lease-lock-namespace", "", "the lease lock resource namespace")
	flag.Parse()

	if id == "" {
		klog.Fatal("unable to get id (missing id flag).")
	}
	if leaseLockName == "" {
		klog.Fatal("unable to get lease lock resource name (missing lease-lock-name flag).")
	}
	if leaseLockNamespace == "" {
		klog.Fatal("unable to get lease lock resource namespace (missing lease-lock-namespace flag).")
	}

	// leader election uses the Kubernetes API by writing to a
	// lock object, which can be a LeaseLock object (preferred),
	// a ConfigMap, or an Endpoints (deprecated) object.
	// Conflicting writes are detected and each client handles those actions
	// independently.
	config, err := buildConfig(kubeconfig)
	if err != nil {
		klog.Fatal(err)
	}
	client := clientset.NewForConfigOrDie(config)

	// use a Go context so we can tell the leaderelection code when we
	// want to step down
	ctx, cancel := context.WithCancel(context.Background())
	defer cancel()

	// listen for interrupts or the Linux SIGTERM signal and cancel
	// our context, which the leader election code will observe and
	// step down
	stoppedCh := make(chan os.Signal, 1)
	defer close(stoppedCh)
	signal.Notify(stoppedCh, os.Interrupt, syscall.SIGTERM)
	go func() {
		<-stoppedCh
		klog.Info("Received termination, signaling shutdown")
		cancel()
	}()

	// Setup any healthz checks we will want to use.
	var checks []healthz.HealthChecker
	var electionChecker *leaderelection.HealthzAdaptor
	electionChecker = leaderelection.NewLeaderHealthzAdaptor(time.Second * 20)
	checks = append(checks, electionChecker)

	mux := http.NewServeMux()
	healthz.InstallPathHandler(mux, "/healthz", checks...)

	server := &http.Server{
		Addr:    fmt.Sprintf(":%d", port),
		Handler: mux,
	}

	go func() {
		klog.Infof("Start listening to %d", port)

		if err := server.ListenAndServe(); err != nil {
			klog.Fatalf("Error starting server: %v", err)
		}
	}()

	// complete your controller loop here
	run := func(ctx context.Context) {
		klog.Info("Controller loop...")

		select {}
	}

	klog.Infof("Run with leader election")

	// we use the Lease lock type since edits to Leases are less common
	// and fewer objects in the cluster watch "all Leases".
	lock := &resourcelock.LeaseLock{
		LeaseMeta: metav1.ObjectMeta{
			Name:      leaseLockName,
			Namespace: leaseLockNamespace,
		},
		Client: client.CoordinationV1(),
		LockConfig: resourcelock.ResourceLockConfig{
			Identity: id,
		},
	}

	// start the leader election code loop
	leaderelection.RunOrDie(ctx, leaderelection.LeaderElectionConfig{
		Lock: lock,
		// IMPORTANT: you MUST ensure that any code you have that
		// is protected by the lease must terminate **before**
		// you call cancel. Otherwise, you could have a background
		// loop still running and another process could
		// get elected before your background loop finished, violating
		// the stated goal of the lease.
		ReleaseOnCancel: true,
		LeaseDuration:   60 * time.Second,
		RenewDeadline:   15 * time.Second,
		RetryPeriod:     5 * time.Second,
		Callbacks: leaderelection.LeaderCallbacks{
			OnStartedLeading: func(ctx context.Context) {
				// we're notified when we start - this is where you would
				// usually put your code
				run(ctx)
			},
			OnStoppedLeading: func() {
				// we can do cleanup here
				klog.Infof("lost: %s", id)
				os.Exit(0)
			},
			OnNewLeader: func(identity string) {
				// we're notified when new leader elected
				if identity == id {
					// I just got the lock
					return
				}
				klog.Infof("new leader elected: %s", identity)
			},
		},
		WatchDog: electionChecker,
	})
}