WIP adds leader-for-life election

cmd/ansible-operator/main.go

@@ -11,6 +11,7 @@ import (
 	k8sutil "github.com/operator-framework/operator-sdk/pkg/util/k8sutil"
 	sdkVersion "github.com/operator-framework/operator-sdk/version"
 	handler "github.com/water-hole/ansible-operator/pkg/handler"
+	"github.com/water-hole/ansible-operator/pkg/leader"
 	proxy "github.com/water-hole/ansible-operator/pkg/proxy"
 	"github.com/water-hole/ansible-operator/pkg/runner"
 	"k8s.io/apimachinery/pkg/apis/meta/v1/unstructured"
@@ -29,6 +30,11 @@ func printVersion() {
 
 func main() {
 	printVersion()
+	err := leader.Become("ansible-operator-lock")
+	if err != nil {
+		logrus.Fatal(err.Error())
+	}
+
 	done := make(chan error)
 
 	// start the proxy
@@ -41,7 +47,7 @@ func main() {
 	go runSDK(done)
 
 	// wait for either to finish
-	err := <-done
+	err = <-done
 	if err == nil {
 		logrus.Info("Exiting")
 	} else {

pkg/leader/leader.go

@@ -0,0 +1,124 @@
+package leader
+
+import (
+	"io/ioutil"
+	"os"
+	"strings"
+	"time"
+
+	"github.com/operator-framework/operator-sdk/pkg/k8sclient"
+	"github.com/operator-framework/operator-sdk/pkg/sdk"
+	corev1 "k8s.io/api/core/v1"
+	apierrors "k8s.io/apimachinery/pkg/api/errors"
+	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
+
+	"github.com/sirupsen/logrus"
+)
+
+// Become ensures that the current pod is the leader within its namespace. It
+// continuously tries to create a ConfigMap with an agreed-upon name and the
+// current pod set as the owner reference. Only one can exist at a time with
+// the same name, so the pod that successfully creates the ConfigMap is the
+// leader. Upon termination of that pod, the garbage collector will delete the
+// ConfigMap, enabling a different pod to become the leader.
+func Become(name string) error {
+	ns, err := myNS()
+	if err != nil {
+		return err
+	}
+	owner, err := myOwnerRef(ns)
+	if err != nil {
+		return err
+	}
+
+	cm := &corev1.ConfigMap{
+		TypeMeta: metav1.TypeMeta{
+			APIVersion: "v1",
+			Kind:       "ConfigMap",
+		},
+		ObjectMeta: metav1.ObjectMeta{
+			Name:            name,
+			Namespace:       ns,
+			OwnerReferences: []metav1.OwnerReference{owner},
+		},
+	}
+
+	// check for existing lock from this pod, in case we got restarted
+	cmClient, _, err := k8sclient.GetResourceClient("v1", "ConfigMap", ns)
+	if err != nil {
+		logrus.Error("failed to get configmap client")
+		return err
+	}
+	existing, err := cmClient.Get(name, metav1.GetOptions{})
+	switch {
+	case err == nil:
+		for _, existingOwner := range existing.GetOwnerReferences() {
+			if existingOwner.Name == owner.Name {
+				logrus.Info("Found existing lock with my name. I was likely restarted.")
+				logrus.Info("Continuing as the leader.")
+				return nil
+			} else {
+				logrus.Infof("Found existing lock from %s", existingOwner.Name)
+			}
+		}
+	case apierrors.IsNotFound(err):
+		logrus.Info("No pre-existing lock was found.")
+	default:
+		logrus.Error("unknown error trying to get ConfigMap")
+		return err
+	}
+
+	// try to create a lock
+	for {
+		err := sdk.Create(cm)
+		switch {
+		case err == nil:
+			logrus.Info("Became the leader.")
+			return nil
+		case apierrors.IsAlreadyExists(err):
+			logrus.Info("Not the leader. Waiting.")
+			time.Sleep(time.Second * 1)
+		default:
+			logrus.Error("unknown error creating configmap")
+			return err
+		}
+	}
+}
+
+func myNS() (string, error) {
+	nsBytes, err := ioutil.ReadFile("/var/run/secrets/kubernetes.io/serviceaccount/namespace")
+	if err != nil {
+		return "", err
+	}
+	ns := strings.TrimSpace(string(nsBytes))
+	logrus.Infof("found namespace: %s", ns)
+	return ns, nil
+}
+
+func myOwnerRef(ns string) (metav1.OwnerReference, error) {
+	hostname, err := os.Hostname()
+	if err != nil {
+		return metav1.OwnerReference{}, err
+	}
+	logrus.Infof("found hostname: %s", hostname)
+
+	pClient, _, err := k8sclient.GetResourceClient("v1", "Pod", ns)
+	if err != nil {
+		logrus.Error("failed to get pod client")
+		return metav1.OwnerReference{}, err
+	}
+
+	myPod, err := pClient.Get(hostname, metav1.GetOptions{})
+	if err != nil {
+		logrus.Error("failed to get pod")
+		return metav1.OwnerReference{}, err
+	}
+
+	owner := metav1.OwnerReference{
+		APIVersion: myPod.GetAPIVersion(),
+		Kind:       myPod.GetKind(),
+		Name:       myPod.GetName(),
+		UID:        myPod.GetUID(),
+	}
+	return owner, nil
+}