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LeaderElector.java
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LeaderElector.java
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/**
* Copyright (C) 2015 Red Hat, Inc.
*
* 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 io.fabric8.kubernetes.client.extended.leaderelection;
import io.fabric8.kubernetes.client.KubernetesClient;
import io.fabric8.kubernetes.client.KubernetesClientException;
import io.fabric8.kubernetes.client.extended.leaderelection.resourcelock.LeaderElectionRecord;
import io.fabric8.kubernetes.client.extended.leaderelection.resourcelock.Lock;
import io.fabric8.kubernetes.client.extended.leaderelection.resourcelock.LockException;
import io.fabric8.kubernetes.client.utils.Utils;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import java.time.Duration;
import java.time.LocalDateTime;
import java.time.ZoneOffset;
import java.time.ZonedDateTime;
import java.time.temporal.ChronoUnit;
import java.util.Objects;
import java.util.concurrent.CompletableFuture;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.Executor;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicLong;
import java.util.concurrent.atomic.AtomicReference;
import java.util.function.Consumer;
import java.util.function.Supplier;
public class LeaderElector {
private static final Logger LOGGER = LoggerFactory.getLogger(LeaderElector.class);
protected static final Double JITTER_FACTOR = 1.2;
private KubernetesClient kubernetesClient;
private LeaderElectionConfig leaderElectionConfig;
private final AtomicReference<LeaderElectionRecord> observedRecord = new AtomicReference<>();
private final AtomicReference<LocalDateTime> observedTime = new AtomicReference<>();
private final Executor executor;
private boolean stopped;
public LeaderElector(KubernetesClient kubernetesClient, LeaderElectionConfig leaderElectionConfig, Executor executor) {
this.kubernetesClient = kubernetesClient;
this.leaderElectionConfig = leaderElectionConfig;
this.executor = executor;
}
/**
* Starts the leader election loop
* <p>
* {@link #start()} is preferred as it does not hold a thread.
*/
public void run() {
CompletableFuture<?> acquire = start();
try {
acquire.get();
} catch (InterruptedException e) {
acquire.cancel(true);
Thread.currentThread().interrupt();
} catch (ExecutionException e) {
LOGGER.error("Exception during leader election", e);
}
}
/**
* Start a leader elector. The future may be cancelled to stop
* the leader elector.
*
* @return the future
*/
public CompletableFuture<?> start() {
LOGGER.debug("Leader election started");
CompletableFuture<Void> result = new CompletableFuture<>();
CompletableFuture<?> acquireFuture = acquire();
acquireFuture.whenComplete((v, t) -> {
if (t == null) {
CompletableFuture<?> renewFuture = renewWithTimeout();
result.whenComplete((v1, t1) -> renewFuture.cancel(true));
renewFuture.whenComplete((v1, t1) -> {
stopLeading();
if (t1 != null) {
result.completeExceptionally(t1);
} else {
result.complete(null);
}
});
} else {
// there's a possibility that we'll obtain the lock, but get cancelled
// before completing the future
stopLeading();
}
});
result.whenComplete((v, t) -> {
acquireFuture.cancel(true);
});
return result;
}
synchronized private void stopLeading() {
stopped = true;
LeaderElectionRecord current = observedRecord.get();
if (current == null || !isLeader(current)) {
return; // not leading
}
try {
if (leaderElectionConfig.isReleaseOnCancel()) {
release(current);
}
} finally {
// called regardless of isReleaseOnCancel
leaderElectionConfig.getLeaderCallbacks().onStopLeading();
}
}
private void release(LeaderElectionRecord current) {
try {
ZonedDateTime now = now();
final LeaderElectionRecord newLeaderElectionRecord = new LeaderElectionRecord(
null,
Duration.ofSeconds(1),
now,
now,
current.getLeaderTransitions());
newLeaderElectionRecord.setVersion(current.getVersion());
leaderElectionConfig.getLock().update(kubernetesClient, newLeaderElectionRecord);
} catch (LockException | KubernetesClientException e) {
final String lockDescription = leaderElectionConfig.getLock().describe();
LOGGER.error("Exception occurred while releasing lock '{}'", lockDescription, e);
}
}
private CompletableFuture<Void> acquire() {
final String lockDescription = leaderElectionConfig.getLock().describe();
LOGGER.debug("Attempting to acquire leader lease '{}'...", lockDescription);
return loop(completion -> {
try {
if (tryAcquireOrRenew()) {
completion.complete(null);
}
LOGGER.debug("Failed to acquire lease '{}' retrying...", lockDescription);
} catch (LockException | KubernetesClientException exception) {
LOGGER.error("Exception occurred while acquiring lock '{}'", lockDescription, exception);
}
}, () -> jitter(leaderElectionConfig.getRetryPeriod(), JITTER_FACTOR).toMillis(), executor);
}
private CompletableFuture<Void> renewWithTimeout() {
final String lockDescription = leaderElectionConfig.getLock().describe();
LOGGER.debug("Attempting to renew leader lease '{}'...", lockDescription);
AtomicLong renewBy = new AtomicLong(System.currentTimeMillis() + leaderElectionConfig.getRenewDeadline().toMillis());
return loop(completion -> {
if (System.currentTimeMillis() > renewBy.get()) {
LOGGER.debug("Renew deadline reached after {} seconds while renewing lock {}",
leaderElectionConfig.getRenewDeadline().get(ChronoUnit.SECONDS), lockDescription);
completion.complete(null);
return;
}
try {
if (tryAcquireOrRenew()) {
renewBy.set(System.currentTimeMillis() + leaderElectionConfig.getRenewDeadline().toMillis());
} else {
// renewal failed, exit
completion.complete(null);
}
} catch (LockException | KubernetesClientException exception) {
LOGGER.debug("Exception occurred while renewing lock: {}", exception.getMessage(), exception);
}
}, () -> leaderElectionConfig.getRetryPeriod().toMillis(), executor);
}
synchronized boolean tryAcquireOrRenew() throws LockException {
if (stopped) {
return false;
}
final Lock lock = leaderElectionConfig.getLock();
final ZonedDateTime now = now();
final LeaderElectionRecord oldLeaderElectionRecord = lock.get(kubernetesClient);
if (oldLeaderElectionRecord == null) {
final LeaderElectionRecord newLeaderElectionRecord = new LeaderElectionRecord(
lock.identity(), leaderElectionConfig.getLeaseDuration(), now, now, 0);
lock.create(kubernetesClient, newLeaderElectionRecord);
updateObserved(newLeaderElectionRecord);
return true;
}
updateObserved(oldLeaderElectionRecord);
final boolean isLeader = isLeader(oldLeaderElectionRecord);
if (!isLeader && !canBecomeLeader(oldLeaderElectionRecord)) {
LOGGER.debug("Lock is held by {} and has not yet expired", oldLeaderElectionRecord.getHolderIdentity());
return false;
}
final LeaderElectionRecord newLeaderElectionRecord = new LeaderElectionRecord(
lock.identity(),
leaderElectionConfig.getLeaseDuration(),
isLeader ? oldLeaderElectionRecord.getAcquireTime() : now,
now,
oldLeaderElectionRecord.getLeaderTransitions() + (isLeader ? 0 : 1));
newLeaderElectionRecord.setVersion(oldLeaderElectionRecord.getVersion());
leaderElectionConfig.getLock().update(kubernetesClient, newLeaderElectionRecord);
updateObserved(newLeaderElectionRecord);
return true;
}
private void updateObserved(LeaderElectionRecord leaderElectionRecord) {
final LeaderElectionRecord current = observedRecord.getAndSet(leaderElectionRecord);
if (!Objects.equals(leaderElectionRecord, current)) {
observedTime.set(LocalDateTime.now());
final String currentLeader = current == null ? null : current.getHolderIdentity();
final String newLeader = leaderElectionRecord.getHolderIdentity();
if (!Objects.equals(newLeader, currentLeader)) {
LOGGER.debug("Leader changed from {} to {}", currentLeader, newLeader);
leaderElectionConfig.getLeaderCallbacks().onNewLeader(newLeader);
if (Objects.equals(currentLeader, leaderElectionConfig.getLock().identity())) {
leaderElectionConfig.getLeaderCallbacks().onStopLeading();
} else if (Objects.equals(newLeader, leaderElectionConfig.getLock().identity())) {
LOGGER.debug("Successfully Acquired leader lease '{}'", leaderElectionConfig.getLock().describe());
leaderElectionConfig.getLeaderCallbacks().onStartLeading();
}
}
}
}
protected final boolean isLeader(LeaderElectionRecord leaderElectionRecord) {
return Objects.equals(leaderElectionConfig.getLock().identity(), leaderElectionRecord.getHolderIdentity());
}
protected final boolean canBecomeLeader(LeaderElectionRecord leaderElectionRecord) {
return Utils.isNullOrEmpty(leaderElectionRecord.getHolderIdentity())
|| !leaderElectionRecord.getRenewTime().plus(leaderElectionConfig.getLeaseDuration()).isAfter(now());
}
/**
* Periodically (every provided period) runs the provided {@link Consumer} in a separate thread
* until the supplied {@link CompletableFuture} is completed.
*
* @param consumer function to run in a separate thread
* @param delaySupplier to schedule the run of the provided consumer
* @return the future to be completed
*/
protected static CompletableFuture<Void> loop(Consumer<CompletableFuture<?>> consumer, Supplier<Long> delaySupplier,
Executor executor) {
CompletableFuture<Void> completion = new CompletableFuture<>();
Utils.scheduleWithVariableRate(completion, executor, () -> consumer.accept(completion), 0,
delaySupplier,
TimeUnit.MILLISECONDS);
return completion;
}
protected static ZonedDateTime now() {
return ZonedDateTime.now(ZoneOffset.UTC);
}
/**
* Returns a {@link Duration} between the provided duration and (duration + maxFactor*duration)
*
* @param duration to apply jitter to
* @param maxFactor for jitter
* @return the jittered duration
*/
protected static Duration jitter(Duration duration, double maxFactor) {
maxFactor = maxFactor > 0 ? maxFactor : 1.0;
return duration.plusMillis(Double.valueOf(duration.toMillis() * Math.random() * maxFactor).longValue());
}
}