Examples of org.apache.hadoop.ha.ActiveStandbyElector

org.apache.hadoop.ha.ActiveStandbyElector
This class implements a simple library to perform leader election on top of Apache Zookeeper. Using Zookeeper as a coordination service, leader election can be performed by atomically creating an ephemeral lock file (znode) on Zookeeper. The service instance that successfully creates the znode becomes active and the rest become standbys.
This election mechanism is only efficient for small number of election candidates (order of 10's) because contention on single znode by a large number of candidates can result in Zookeeper overload.
The elector does not guarantee fencing (protection of shared resources) among service instances. After it has notified an instance about becoming a leader, then that instance must ensure that it meets the service consistency requirements. If it cannot do so, then it is recommended to quit the election. The application implements the {@link ActiveStandbyElectorCallback}to interact with the elector

    List<ZKUtil.ZKAuthInfo> zkAuths = RMZKUtils.getZKAuths(conf);


    int maxRetryNum = conf.getInt(
        CommonConfigurationKeys.HA_FC_ELECTOR_ZK_OP_RETRIES_KEY,
        CommonConfigurationKeys.HA_FC_ELECTOR_ZK_OP_RETRIES_DEFAULT);
    elector = new ActiveStandbyElector(zkQuorum, (int) zkSessionTimeout,
        electionZNode, zkAcls, zkAuths, this, maxRetryNum);


    elector.ensureParentZNode();
    if (!isParentZnodeSafe(clusterId)) {
      notifyFatalError(electionZNode + " znode has invalid data! "+

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    }


    // TODO (YARN-1528): ZKAuthInfo to be set for rm-store and elector
    List<ZKUtil.ZKAuthInfo> zkAuths = Collections.emptyList();


    elector = new ActiveStandbyElector(zkQuorum, (int) zkSessionTimeout,
        electionZNode, zkAcls, zkAuths, this);


    elector.ensureParentZNode();
    if (!isParentZnodeSafe(clusterId)) {
      notifyFatalError(electionZNode + " znode has invalid data! "+

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        YarnConfiguration.DEFAULT_RM_ZK_TIMEOUT_MS);


    List<ACL> zkAcls = RMZKUtils.getZKAcls(conf);
    List<ZKUtil.ZKAuthInfo> zkAuths = RMZKUtils.getZKAuths(conf);


    elector = new ActiveStandbyElector(zkQuorum, (int) zkSessionTimeout,
        electionZNode, zkAcls, zkAuths, this);


    elector.ensureParentZNode();
    if (!isParentZnodeSafe(clusterId)) {
      notifyFatalError(electionZNode + " znode has invalid data! "+

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        YarnConfiguration.DEFAULT_RM_ZK_TIMEOUT_MS);


    List<ACL> zkAcls = RMZKUtils.getZKAcls(conf);
    List<ZKUtil.ZKAuthInfo> zkAuths = RMZKUtils.getZKAuths(conf);


    elector = new ActiveStandbyElector(zkQuorum, (int) zkSessionTimeout,
        electionZNode, zkAcls, zkAuths, this);


    elector.ensureParentZNode();
    if (!isParentZnodeSafe(clusterId)) {
      notifyFatalError(electionZNode + " znode has invalid data! "+

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org.apache.hadoop.yarn.server.resourcemanager.EmbeddedElectorService

org.apache.zookeeper.data.Stat

org.apache.zookeeper.KeeperException.Code

org.apache.zookeeper.ZooKeeper

org.apache.hadoop.HadoopIllegalArgumentException

java.io.IOException

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