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leader.go
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leader.go
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// Copyright 2018 The Operator-SDK 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 leader
import (
"context"
"time"
"github.com/operator-framework/operator-sdk/pkg/k8sutil"
corev1 "k8s.io/api/core/v1"
apierrors "k8s.io/apimachinery/pkg/api/errors"
metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
"k8s.io/apimachinery/pkg/util/wait"
crclient "sigs.k8s.io/controller-runtime/pkg/client"
"sigs.k8s.io/controller-runtime/pkg/client/config"
logf "sigs.k8s.io/controller-runtime/pkg/runtime/log"
)
var log = logf.Log.WithName("leader")
// maxBackoffInterval defines the maximum amount of time to wait between
// attempts to become the leader.
const maxBackoffInterval = time.Second * 16
// Become ensures that the current pod is the leader within its namespace. If
// run outside a cluster, it will skip leader election and return nil. It
// continuously tries to create a ConfigMap with the provided 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(ctx context.Context, lockName string) error {
log.Info("Trying to become the leader.")
ns, err := k8sutil.GetOperatorNamespace()
if err != nil {
if err == k8sutil.ErrNoNamespace {
log.Info("Skipping leader election; not running in a cluster.")
return nil
}
return err
}
config, err := config.GetConfig()
if err != nil {
return err
}
client, err := crclient.New(config, crclient.Options{})
if err != nil {
return err
}
owner, err := myOwnerRef(ctx, client, ns)
if err != nil {
return err
}
// check for existing lock from this pod, in case we got restarted
existing := &corev1.ConfigMap{
TypeMeta: metav1.TypeMeta{
APIVersion: "v1",
Kind: "ConfigMap",
},
}
key := crclient.ObjectKey{Namespace: ns, Name: lockName}
err = client.Get(ctx, key, existing)
switch {
case err == nil:
for _, existingOwner := range existing.GetOwnerReferences() {
if existingOwner.Name == owner.Name {
log.Info("Found existing lock with my name. I was likely restarted.")
log.Info("Continuing as the leader.")
return nil
} else {
log.Info("Found existing lock", "LockOwner", existingOwner.Name)
}
}
case apierrors.IsNotFound(err):
log.Info("No pre-existing lock was found.")
default:
log.Error(err, "Unknown error trying to get ConfigMap")
return err
}
cm := &corev1.ConfigMap{
TypeMeta: metav1.TypeMeta{
APIVersion: "v1",
Kind: "ConfigMap",
},
ObjectMeta: metav1.ObjectMeta{
Name: lockName,
Namespace: ns,
OwnerReferences: []metav1.OwnerReference{*owner},
},
}
// try to create a lock
backoff := time.Second
for {
err := client.Create(ctx, cm)
switch {
case err == nil:
log.Info("Became the leader.")
return nil
case apierrors.IsAlreadyExists(err):
log.Info("Not the leader. Waiting.")
select {
case <-time.After(wait.Jitter(backoff, .2)):
if backoff < maxBackoffInterval {
backoff *= 2
}
continue
case <-ctx.Done():
return ctx.Err()
}
default:
log.Error(err, "Unknown error creating ConfigMap")
return err
}
}
}
// myOwnerRef returns an OwnerReference that corresponds to the pod in which
// this code is currently running.
// It expects the environment variable POD_NAME to be set by the downwards API
func myOwnerRef(ctx context.Context, client crclient.Client, ns string) (*metav1.OwnerReference, error) {
myPod, err := k8sutil.GetPod(ctx, client, ns)
if err != nil {
return nil, err
}
owner := &metav1.OwnerReference{
APIVersion: "v1",
Kind: "Pod",
Name: myPod.ObjectMeta.Name,
UID: myPod.ObjectMeta.UID,
}
return owner, nil
}