聊聊scalecubecluster的FailureDetector

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本文主要研究一下 scalecube-cluster 的 FailureDetector

FailureDetector

scalecube-cluster-2.2.5/cluster/src/main/java/io/scalecube/cluster/fdetector/FailureDetector.java

/**
 * Failure Detector component responsible for monitoring availability of other members in the
 * cluster. This interface is supposed to be used internally as part cluster membership protocol. It
 * doesn't specify that particular node is failed, but just provide information that either it is
 * suspected or trusted at current moment of time. So it is up to cluster membership or other top
 * level component to define when suspected member is actually failed.
 */
public interface FailureDetector {

  /**
   * Starts running failure detection algorithm. After started it begins to receive and send ping
   * messages.
   */
  void start();

  /** Stops running failure detection algorithm and releases occupied resources. */
  void stop();

  /** Listens for results of ping checks (ALIVE/SUSPECT) done periodically by failure detector. */
  Flux<FailureDetectorEvent> listen();}
  • FailureDetector 定义了 start、stop、listen 方法

FailureDetectorImpl

scalecube-cluster-2.2.5/cluster/src/main/java/io/scalecube/cluster/fdetector/FailureDetectorImpl.java

public final class FailureDetectorImpl implements FailureDetector {private static final Logger LOGGER = LoggerFactory.getLogger(FailureDetectorImpl.class);

  // Qualifiers

  public static final String PING = "sc/fdetector/ping";
  public static final String PING_REQ = "sc/fdetector/pingReq";
  public static final String PING_ACK = "sc/fdetector/pingAck";

  // Injected

  private final Member localMember;
  private final Transport transport;
  private final FailureDetectorConfig config;
  private final CorrelationIdGenerator cidGenerator;

  // State

  private long currentPeriod = 0;
  private List<Member> pingMembers = new ArrayList<>();
  private int pingMemberIndex = 0; // index for sequential ping member selection

  // Disposables

  private final Disposable.Composite actionsDisposables = Disposables.composite();

  // Subject
  private final FluxProcessor<FailureDetectorEvent, FailureDetectorEvent> subject =
      DirectProcessor.<FailureDetectorEvent>create().serialize();

  private final FluxSink<FailureDetectorEvent> sink = subject.sink();

  // Scheduled
  private final Scheduler scheduler;

  /**
   * Creates new instance of failure detector with given transport and settings.
   *
   * @param localMember local cluster member
   * @param transport cluster transport
   * @param membershipProcessor membership event processor
   * @param config failure detector settings
   * @param scheduler scheduler
   * @param cidGenerator correlationId generator
   */
  public FailureDetectorImpl(
      Member localMember,
      Transport transport,
      Flux<MembershipEvent> membershipProcessor,
      FailureDetectorConfig config,
      Scheduler scheduler,
      CorrelationIdGenerator cidGenerator) {this.localMember = Objects.requireNonNull(localMember);
    this.transport = Objects.requireNonNull(transport);
    this.config = Objects.requireNonNull(config);
    this.scheduler = Objects.requireNonNull(scheduler);
    this.cidGenerator = Objects.requireNonNull(cidGenerator);

    // Subscribe
    actionsDisposables.addAll(
        Arrays.asList(
            membershipProcessor //
                .publishOn(scheduler)
                .subscribe(this::onMemberEvent, this::onError),
            transport
                .listen() //
                .publishOn(scheduler)
                .subscribe(this::onMessage, this::onError)));
  }

  @Override
  public void start() {
    actionsDisposables.add(
        scheduler.schedulePeriodically(
            this::doPing,
            config.getPingInterval(),
            config.getPingInterval(),
            TimeUnit.MILLISECONDS));
  }

  @Override
  public void stop() {
    // Stop accepting requests and sending pings
    actionsDisposables.dispose();

    // Stop publishing events
    sink.complete();}

  @Override
  public Flux<FailureDetectorEvent> listen() {return subject.onBackpressureBuffer();
  }

  //......

}
  • FailureDetectorImpl 实现了 FailureDetector 接口；它定义了 3 个 message 的 qualifier 分别是 PING、PING_REQ、PING_ACK；同时也定义了 pingMembers 列表
  • FailureDetectorImpl 的构造器订阅了 membershipProcessor 触发 onMemberEvent 方法，订阅了 transport.listen() 触发 onMessage 方法
  • start 方法通过 scheduler.schedulePeriodically 注册了 doPing 任务，每隔 pingInterval 执行，默认是 5000ms；stop 方法会执行 actionsDisposables.dispose() 及 sink.complete()；listen() 则返回 subject.onBackpressureBuffer()

onMemberEvent

scalecube-cluster-2.2.5/cluster/src/main/java/io/scalecube/cluster/fdetector/FailureDetectorImpl.java

public final class FailureDetectorImpl implements FailureDetector {
  //......

  private void onMemberEvent(MembershipEvent event) {Member member = event.member();
    if (event.isRemoved()) {pingMembers.remove(member);
    }
    if (event.isAdded()) {
      // insert member into random positions
      int size = pingMembers.size();
      int index = size > 0 ? ThreadLocalRandom.current().nextInt(size) : 0;
      pingMembers.add(index, member);
    }
  }

  //......
}
  • onMemberEvent 会根据 MembershipEvent 来移除或使用随机的 index 添加 member 到 pingMembers 中

onMessage

scalecube-cluster-2.2.5/cluster/src/main/java/io/scalecube/cluster/fdetector/FailureDetectorImpl.java

public final class FailureDetectorImpl implements FailureDetector {
  //......

  private void onMessage(Message message) {if (isPing(message)) {onPing(message);
    } else if (isPingReq(message)) {onPingReq(message);
    } else if (isTransitPingAck(message)) {onTransitPingAck(message);
    }
  }

  private boolean isPing(Message message) {return PING.equals(message.qualifier());
  }

  private boolean isPingReq(Message message) {return PING_REQ.equals(message.qualifier());
  }

  private boolean isTransitPingAck(Message message) {return PING_ACK.equals(message.qualifier())
        && message.<PingData>data().getOriginalIssuer() != null;
  }

  /** Listens to PING message and answers with ACK. */
  private void onPing(Message message) {
    long period = this.currentPeriod;
    LOGGER.trace("Received Ping[{}]", period);
    PingData data = message.data();
    if (!data.getTo().id().equals(localMember.id())) {
      LOGGER.warn("Received Ping[{}] to {}, but local member is {}", period, data.getTo(), localMember);
      return;
    }
    String correlationId = message.correlationId();
    Message ackMessage =
        Message.withData(data)
            .qualifier(PING_ACK)
            .correlationId(correlationId)
            .sender(localMember.address())
            .build();
    Address address = data.getFrom().address();
    LOGGER.trace("Send PingAck[{}] to {}", period, address);
    transport
        .send(address, ackMessage)
        .subscribe(
            null,
            ex ->
                LOGGER.debug("Failed to send PingAck[{}] to {}, cause: {}", period, address, ex.toString()));
  }

  /** Listens to PING_REQ message and sends PING to requested cluster member. */
  private void onPingReq(Message message) {
    long period = this.currentPeriod;
    LOGGER.trace("Received PingReq[{}]", period);
    PingData data = message.data();
    Member target = data.getTo();
    Member originalIssuer = data.getFrom();
    String correlationId = message.correlationId();
    PingData pingReqData = new PingData(localMember, target, originalIssuer);
    Message pingMessage =
        Message.withData(pingReqData)
            .qualifier(PING)
            .correlationId(correlationId)
            .sender(localMember.address())
            .build();
    Address address = target.address();
    LOGGER.trace("Send transit Ping[{}] to {}", period, address);
    transport
        .send(address, pingMessage)
        .subscribe(
            null,
            ex ->
                LOGGER.debug("Failed to send transit Ping[{}] to {}, cause: {}",
                    period,
                    address,
                    ex.toString()));
  }

  /**
   * Listens to ACK with message containing ORIGINAL_ISSUER then converts message to plain ACK and
   * sends it to ORIGINAL_ISSUER.
   */
  private void onTransitPingAck(Message message) {
    long period = this.currentPeriod;
    LOGGER.trace("Received transit PingAck[{}]", period);
    PingData data = message.data();
    Member target = data.getOriginalIssuer();
    String correlationId = message.correlationId();
    PingData originalAckData = new PingData(target, data.getTo());
    Message originalAckMessage =
        Message.withData(originalAckData)
            .qualifier(PING_ACK)
            .correlationId(correlationId)
            .sender(localMember.address())
            .build();
    Address address = target.address();
    LOGGER.trace("Resend transit PingAck[{}] to {}", period, address);
    transport
        .send(address, originalAckMessage)
        .subscribe(
            null,
            ex ->
                LOGGER.debug("Failed to resend transit PingAck[{}] to {}, cause: {}",
                    period,
                    address,
                    ex.toString()));
  }

  //......

}
  • onMessage 方法则根据消息的不同 qualifier 及 originalIssuer 信息来判断执行 onPing 或 onPingReq 或 onTransitPingAck 方法；onPing 方法会返回 PING_ACK 消息给 sender；onPingReq 方法则会发送 PING 给 pingReq 指定的 member；onTransitPingAck 方法则会将 pingReq 请求返回的 ack 再转发回给 originalIssuer

doPing

scalecube-cluster-2.2.5/cluster/src/main/java/io/scalecube/cluster/fdetector/FailureDetectorImpl.java

public final class FailureDetectorImpl implements FailureDetector {
  //......

  private void doPing() {
    // Increment period counter
    long period = currentPeriod++;

    // Select ping member
    Member pingMember = selectPingMember();
    if (pingMember == null) {return;}

    // Send ping
    String cid = cidGenerator.nextCid();
    PingData pingData = new PingData(localMember, pingMember);
    Message pingMsg =
        Message.withData(pingData)
            .qualifier(PING)
            .correlationId(cid)
            .sender(localMember.address())
            .build();

    LOGGER.trace("Send Ping[{}] to {}", period, pingMember);
    Address address = pingMember.address();
    transport
        .requestResponse(pingMsg, address)
        .timeout(Duration.ofMillis(config.getPingTimeout()), scheduler)
        .publishOn(scheduler)
        .subscribe(
            message -> {LOGGER.trace("Received PingAck[{}] from {}", period, pingMember);
              publishPingResult(period, pingMember, MemberStatus.ALIVE);
            },
            ex -> {
              LOGGER.debug("Failed to get PingAck[{}] from {} within {} ms",
                  period,
                  pingMember,
                  config.getPingTimeout());

              final int timeLeft = config.getPingInterval() - config.getPingTimeout();
              final List<Member> pingReqMembers = selectPingReqMembers(pingMember);

              if (timeLeft <= 0 || pingReqMembers.isEmpty()) {LOGGER.trace("No PingReq[{}] occurred", period);
                publishPingResult(period, pingMember, MemberStatus.SUSPECT);
              } else {doPingReq(currentPeriod, pingMember, pingReqMembers, cid);
              }
            });
  }

  private Member selectPingMember() {if (pingMembers.isEmpty()) {return null;}
    if (pingMemberIndex >= pingMembers.size()) {
      pingMemberIndex = 0;
      Collections.shuffle(pingMembers);
    }
    return pingMembers.get(pingMemberIndex++);
  }

  private List<Member> selectPingReqMembers(Member pingMember) {if (config.getPingReqMembers() <= 0) {return Collections.emptyList();
    }
    List<Member> candidates = new ArrayList<>(pingMembers);
    candidates.remove(pingMember);
    if (candidates.isEmpty()) {return Collections.emptyList();
    }
    Collections.shuffle(candidates);
    boolean selectAll = candidates.size() < config.getPingReqMembers();
    return selectAll ? candidates : candidates.subList(0, config.getPingReqMembers());
  }

  private void doPingReq(long period, final Member pingMember, final List<Member> pingReqMembers, String cid) {
    Message pingReqMsg =
        Message.withData(new PingData(localMember, pingMember))
            .qualifier(PING_REQ)
            .correlationId(cid)
            .sender(localMember.address())
            .build();
    LOGGER.trace("Send PingReq[{}] to {} for {}", period, pingReqMembers, pingMember);

    Duration timeout = Duration.ofMillis(config.getPingInterval() - config.getPingTimeout());
    pingReqMembers.forEach(
        member ->
            transport
                .requestResponse(pingReqMsg, member.address())
                .timeout(timeout, scheduler)
                .publishOn(scheduler)
                .subscribe(
                    message -> {
                      LOGGER.trace("Received transit PingAck[{}] from {} to {}",
                          period,
                          message.sender(),
                          pingMember);
                      publishPingResult(period, pingMember, MemberStatus.ALIVE);
                    },
                    throwable -> {
                      LOGGER.trace("Timeout getting transit PingAck[{}] from {} to {} within {} ms",
                          period,
                          pingReqMembers,
                          pingMember,
                          timeout);
                      publishPingResult(period, pingMember, MemberStatus.SUSPECT);
                    }));
  }

  private void publishPingResult(long period, Member member, MemberStatus status) {LOGGER.debug("Member {} detected as {} at [{}]", member, status, period);
    sink.next(new FailureDetectorEvent(member, status));
  }

  //......

}
  • doPing 方法首先递增 currentPeriod，然后通过 selectPingMember 随机选择 pingMember，之后构造 pingData，然后通过 transport.requestResponse 发送请求，请求成功时执行 publishPingResult，异常情况下则通过 selectPingReqMembers 随机选择 pingReqMembers，在 config.getPingInterval() – config.getPingTimeout() 小于等于 0 或者 pingReqMembers 为空时则执行 publishPingResult(period, pingMember, MemberStatus.SUSPECT)，否则进行 doPingReq
  • selectPingMember 方法在 pingMemberIndex 大于等于 pingMembers.size() 的时候会重置该 index 为 0，并执行 Collections.shuffle(pingMembers)，之后递增 pingMemberIndex；selectPingReqMembers 方法则基于 pingMembers 创建新的 list 然后移除 pingMember 得到 candidates，之后进行 Collections.shuffle(candidates)，然后根据 config.getPingReqMembers() 来 subList 该 candidates 列表得到 pingReqMembers
  • onPingReq 方法则遍历 pingReqMembers 对其发送 pingReqMsg，当接收到 transit PingAck 时则执行 publishPingResult(period, pingMember, MemberStatus.ALIVE)，出现异常时执行 publishPingResult(period, pingMember, MemberStatus.SUSPECT)；publishPingResult 方法往 sink 里头放入 FailureDetectorEvent 事件

小结

  • FailureDetector 定义了 start、stop、listen 方法；FailureDetectorImpl 实现了 FailureDetector 接口；它定义了 3 个 message 的 qualifier 分别是 PING、PING_REQ、PING_ACK；同时也定义了 pingMembers 列表；FailureDetectorImpl 的构造器订阅了 membershipProcessor 触发 onMemberEvent 方法，订阅了 transport.listen() 触发 onMessage 方法；start 方法通过 scheduler.schedulePeriodically 注册了 doPing 任务，每隔 pingInterval 执行，默认是 5000ms；stop 方法会执行 actionsDisposables.dispose() 及 sink.complete()；listen() 则返回 subject.onBackpressureBuffer()
  • onMemberEvent 会根据 MembershipEvent 来移除或使用随机的 index 添加 member 到 pingMembers 中；onMessage 方法则根据消息的不同 qualifier 及 originalIssuer 信息来判断执行 onPing 或 onPingReq 或 onTransitPingAck 方法；onPing 方法会返回 PING_ACK 消息给 sender；onPingReq 方法则会发送 PING 给 pingReq 指定的 member；onTransitPingAck 方法则会将 pingReq 请求返回的 ack 再转发回给 originalIssuer
  • doPing 方法首先递增 currentPeriod，然后通过 selectPingMember 随机选择 pingMember，之后构造 pingData，然后通过 transport.requestResponse 发送请求，请求成功时执行 publishPingResult，异常情况下则通过 selectPingReqMembers 随机选择 pingReqMembers，在 config.getPingInterval() – config.getPingTimeout() 小于等于 0 或者 pingReqMembers 为空时则执行 publishPingResult(period, pingMember, MemberStatus.SUSPECT)，否则进行 doPingReq

doc

  • FailureDetector
  • FailureDetectorImpl
  • FailureDetectorEvent

正文完
distributed-systems
发表至：无分类
2019-05-05
 0