HA（High Available），即高可用（7*24小时不中断服务）
单点故障即有一台机器挂了导致全部都挂了；HA就是解决单点故障，就是针对NameNode；
主Active：读写、从standby只读；所依赖的服务都必须是高可用的；
两种解决共享空间的方案：NFS、QJM（主流的）
奇数台机器；QJM跟zookeeper（数据全局一致；半数以上的机器存活就可以提供服务）高可用的方式一模一样，；
QJM也是基于Paxos算法，系统容错不能超过n-1/2， 5台容错2台；
这个架构只能手动决定哪个是active哪个是standby；必须只能有一个active！！如果出现两个NameNode，即两个都是active，它可能还不报错，那么可能会导致整个集群的数据都是错的，问题很严重！两个AA的情况叫脑裂（split brain缩写sb）。
standby要想变成active，要确保active那个，需要安全可靠的zookeeper（文件系统+通知机制）第三方来联系两方 ---> 实现故障的自动转移；
由Zkfc来联系zookeeper，并不是namenode直接联系，（zookeeper客户端）；HA是hadoop2.0才有的，namenode在1.0时就有了；没有把zkfc写进namenode是为了保持NameNode的健壮性，没有zkfc之前就已经运行的很好了（鲁棒性）；NameNode和Zkfc虽然是两个进程但它们是绑定到一起的。
两个zkfc怎么决定谁初始化就是active呢，谁快谁就是active； 是active状态它会在zookeeper中有一个临时节点，zkfc会尝试看看zookeeper中有没有这个临时节点，如果没有我就变成这个临时节点，成为active，慢的一看有了，就变成standby；
NameNode发生假死，zkfc就会把zookeeper中的临时节点删除，去通知另外一个namenode的zkfc，让它去成为active，这个namenode就会去强行杀死假死的namenode，防止脑裂！如果杀不死就自定义一个脚本强制它关机，成功之后才会变成active。
现在合并fsimage是由standby来完成的，没有secondaryNameNode；
在module目录下创建一个ha文件夹
mkdir ha
将/opt/module/下的 hadoop-2.7.2拷贝到/opt/module/ha目录下
cp -r hadoop-2.7.2/ /opt/module/ha/
删除data logs等文件
配置core-site.xml
<configuration>
<!-- 把两个NameNode）的地址组装成一个集群mycluster -->
<property>
<name>fs.defaultFS</name>
<value>hdfs://mycluster</value>
</property>
<!-- 指定hadoop运行时产生文件的存储目录 -->
<property>
<name>hadoop.tmp.dir</name>
<value>/opt/module/ha/hadoop-2.7.2/data/tmp</value>
</property>
<property>
<name>ha.zookeeper.quorum</name>
<value>hadoop101:2181,hadoop102:2181,hadoop103:2181</value>
</property>
</configuration>
配置hdfs-site.xml
<configuration>
<!-- 完全分布式集群名称 -->
<property>
<name>dfs.nameservices</name>
<value>mycluster</value>
</property>
<!-- 集群中NameNode节点都有哪些 -->
<property>
<name>dfs.ha.namenodes.mycluster</name>
<value>nn1,nn2</value>
</property>
<!-- nn1的RPC通信地址 -->
<property>
<name>dfs.namenode.rpc-address.mycluster.nn1</name>
<value>hadoop101:9000</value>
</property>
<!-- nn2的RPC通信地址 -->
<property>
<name>dfs.namenode.rpc-address.mycluster.nn2</name>
<value>hadoop102:9000</value>
</property>
<!-- nn1的http通信地址 -->
<property>
<name>dfs.namenode.http-address.mycluster.nn1</name>
<value>hadoop101:50070</value>
</property>
<!-- nn2的http通信地址 -->
<property>
<name>dfs.namenode.http-address.mycluster.nn2</name>
<value>hadoop102:50070</value>
</property>
<!-- 指定NameNode元数据在JournalNode上的存放位置 -->
<property>
<name>dfs.namenode.shared.edits.dir</name>
<value>qjournal://hadoop101:8485;hadoop102:8485;hadoop103:8485/mycluster</value>
</property>
<!-- 配置隔离机制，即同一时刻只能有一台服务器对外响应 -->
<property>
<name>dfs.ha.fencing.methods</name>
<value>sshfence</value>
</property>
<!-- 使用隔离机制时需要ssh无秘钥登录-->
<property>
<name>dfs.ha.fencing.ssh.private-key-files</name>
<value>/home/kris/.ssh/id_rsa</value>
</property>
<!-- 声明journalnode服务器存储目录-->
<property>
<name>dfs.journalnode.edits.dir</name>
<value>/opt/module/ha/hadoop-2.7.2/data/jn</value>
</property>
<!-- 关闭权限检查-->
<property>
<name>dfs.permissions.enable</name>
<value>false</value>
</property>
<!-- 访问代理类：client，mycluster，active配置失败自动切换实现方式-->
<property>
<name>dfs.client.failover.proxy.provider.mycluster</name>
<value>org.apache.hadoop.hdfs.server.namenode.ha.ConfiguredFailoverProxyProvider</value>
</property>
<property>
<name>dfs.ha.automatic-failover.enabled</name>
<value>true</value>
</property>
</configuration>
发送到其他机器
xsync ha
启动HDFS-HA集群
1. 在各个JournalNode节点上，输入以下命令启动journalnode服务
sbin/hadoop-daemons.sh start journalnode //加个s就可以3台一块启动；都启动之后才能格式化namenode；只能格式化一次！
2. 在[nn1]上，对其进行格式化，并启动
bin/hdfs namenode -format
19/02/13 02:15:00 INFO util.GSet: Computing capacity for map NameNodeRetryCache
19/02/13 02:15:00 INFO util.GSet: VM type = 64-bit
19/02/13 02:15:00 INFO util.GSet: 0.029999999329447746% max memory 889 MB = 273.1 KB
19/02/13 02:15:00 INFO util.GSet: capacity = 2^15 = 32768 entries
19/02/13 02:15:01 INFO namenode.FSImage: Allocated new BlockPoolId: BP-26035536-192.168.1.101-1549995301800
19/02/13 02:15:01 INFO common.Storage: Storage directory /opt/module/ha/hadoop-2.7.2/data/tmp/dfs/name has been successfully formatted.
19/02/13 02:15:02 INFO namenode.NNStorageRetentionManager: Going to retain 1 images with txid >= 0
19/02/13 02:15:02 INFO util.ExitUtil: Exiting with status 0
19/02/13 02:15:02 INFO namenode.NameNode: SHUTDOWN_MSG:
/************************************************************
SHUTDOWN_MSG: Shutting down NameNode at hadoop101/192.168.1.101
************************************************************/
sbin/hadoop-daemon.sh start namenode
3. 在[nn2]上，同步nn1的元数据信息
bin/hdfs namenode -bootstrapStandby
19/02/13 02:16:51 INFO common.Storage: Storage directory /opt/module/ha/hadoop-2.7.2/data/tmp/dfs/name has been successfully formatted.
19/02/13 02:16:51 INFO namenode.TransferFsImage: Opening connection to http://hadoop101:50070/imagetransfer?getimage=1&txid=0&storageInfo=-63:1640720426:0:CID-81cbaa0d-6a6f-4932-98ba-ff2a46d87514
19/02/13 02:16:51 INFO namenode.TransferFsImage: Image Transfer timeout configured to 60000 milliseconds
19/02/13 02:16:52 INFO namenode.TransferFsImage: Transfer took 0.02s at 0.00 KB/s
19/02/13 02:16:52 INFO namenode.TransferFsImage: Downloaded file fsimage.ckpt_0000000000000000000 size 351 bytes.
19/02/13 02:16:52 INFO util.ExitUtil: Exiting with status 0
19/02/13 02:16:52 INFO namenode.NameNode: SHUTDOWN_MSG:
/************************************************************
SHUTDOWN_MSG: Shutting down NameNode at hadoop102/192.168.1.102
************************************************************/
4. 启动[nn2]
sbin/hadoop-daemon.sh start namenode
6. 在[nn1]上，启动所有datanode； hadoop-daemons.sh是3台都启动datanode
sbin/hadoop-daemons.sh start datanode
7. 将[nn1]切换为Active
bin/hdfs haadmin -transitionToActive nn1
5. 查看是否Active
bin/hdfs haadmin -getServiceState nn1
http://hadoop101:50070/dfshealth.html#tab-overview
http://hadoop102:50070/dfshealth.html#tab-overview
配置HDFS-HA自动故障转移
配置HDFS-HA自动故障转移
1. 具体配置
（1）在hdfs-site.xml中增加
<property>
<name>dfs.ha.automatic-failover.enabled</name>
<value>true</value>
</property>
（2）在core-site.xml文件中增加
<property>
<name>ha.zookeeper.quorum</name>
<value>hadoop101:2181,hadoop102:2181,hadoop103:2181</value>
</property>
2. 启动
（1）关闭所有HDFS服务：
sbin/stop-dfs.sh
（2）启动Zookeeper集群：
bin/zkServer.sh start
（3）初始化HA在Zookeeper中状态：(只初始化一次)
bin/hdfs zkfc -formatZK
19/02/13 02:04:02 INFO zookeeper.ClientCnxn: Socket connection established to hadoop102/192.168.1.102:2181, initiating session
19/02/13 02:04:02 INFO zookeeper.ClientCnxn: Session establishment complete on server hadoop102/192.168.1.102:2181, sessionid = 0x268e2dee6e40000, negotiated timeout = 5000
19/02/13 02:04:02 INFO ha.ActiveStandbyElector: Session connected.
19/02/13 02:04:02 INFO ha.ActiveStandbyElector: Successfully created /hadoop-ha/mycluster in ZK.
19/02/13 02:04:02 INFO zookeeper.ZooKeeper: Session: 0x268e2dee6e40000 closed
19/02/13 02:04:02 INFO zookeeper.ClientCnxn: EventThread shut down
（4）启动HDFS服务：
sbin/start-dfs.sh
hadoop101: starting namenode, logging to /opt/module/ha/hadoop-2.7.2/logs/hadoop-kris-namenode-hadoop101.out
hadoop102: starting namenode, logging to /opt/module/ha/hadoop-2.7.2/logs/hadoop-kris-namenode-hadoop102.out
hadoop102: starting datanode, logging to /opt/module/ha/hadoop-2.7.2/logs/hadoop-kris-datanode-hadoop102.out
hadoop101: starting datanode, logging to /opt/module/ha/hadoop-2.7.2/logs/hadoop-kris-datanode-hadoop101.out
hadoop103: starting datanode, logging to /opt/module/ha/hadoop-2.7.2/logs/hadoop-kris-datanode-hadoop103.out
Starting journal nodes [hadoop101 hadoop102 hadoop103]
hadoop103: starting journalnode, logging to /opt/module/ha/hadoop-2.7.2/logs/hadoop-kris-journalnode-hadoop103.out
hadoop102: starting journalnode, logging to /opt/module/ha/hadoop-2.7.2/logs/hadoop-kris-journalnode-hadoop102.out
hadoop101: starting journalnode, logging to /opt/module/ha/hadoop-2.7.2/logs/hadoop-kris-journalnode-hadoop101.out
Starting ZK Failover Controllers on NN hosts [hadoop101 hadoop102]
hadoop101: starting zkfc, logging to /opt/module/ha/hadoop-2.7.2/logs/hadoop-kris-zkfc-hadoop101.out
hadoop102: starting zkfc, logging to /opt/module/ha/hadoop-2.7.2/logs/hadoop-kris-zkfc-hadoop102.out
3. 验证
（1）将Active NameNode进程kill
kill -9 namenode的进程id ---> 另外一个namenode上位；( 杀掉之后，可单独启动: sbin/hadoop-daemon.sh start namenode)
(2) 将DFSZKFailoverController的进程kill
kill -9 8819 --->尽管它的namenode没有挂，但另外一个namenode也会上位，它变成standby
启动它要先停止->sbin/stop-dfs.sh sbin/start-dfs.sh
（3）将Active NameNode机器断开网络
sudo service network stop ---> 把网络断开之后，配的隔离机制是sshfence尝试远程登录区杀敌hadoop101，直到把101网络连接上才杀死，102才成为active；
断网上位很容易脑裂，那边网已恢复就炸了；如果真的断网，它这个是不会自动切的是为了防脑裂。虽然可以通过配置断网可以直接上，但很危险；断网上不去反而安全。
[zk: localhost:2181(CONNECTED) 0] ls /
[zookeeper, hadoop-ha]
[zk: localhost:2181(CONNECTED) 1] ls /
[zookeeper, hadoop-ha]
[zk: localhost:2181(CONNECTED) 2] ls /hadoop-ha
[mycluster]
[zk: localhost:2181(CONNECTED) 3] ls /hadoop-ha/mycluster
[ActiveBreadCrumb, ActiveStandbyElectorLock] 选举的关键节点，谁占领了这个节点谁就是active；
[zk: localhost:2181(CONNECTED) 4] get /hadoop-ha/mycluster/ActiveStandbyElectorLock
myclusternn1 hadoop101 �F(�>
cZxid = 0x10000000f
ctime = Wed Feb 13 02:16:22 CST 2019
mZxid = 0x10000000f
mtime = Wed Feb 13 02:16:22 CST 2019
pZxid = 0x10000000f
cversion = 0
dataVersion = 0
aclVersion = 0
ephemeralOwner = 0x268e2dee6e40002 临时节点，
dataLength = 33
numChildren = 0
进程
hadoop101 hadoop102 hadoop103
NameNode NameNode
JournalNode JournalNode JournalNode
DataNode DataNode DataNode
DFSZKFailoverController DFSZKFailoverController ZooKeeperMain（bin/zkCli.sh ,启动zookeeperd客户端）
ResourceManager ResourceManager
NodeManager NodeManager NodeManager
QuorumPeerMain QuorumPeerMain QuorumPeerMain (bin/zkServer.sh start 启动zookeeper服务器)
DFSZKFailoverController是Hadoop-2.7.0中HDFS NameNode HA实现的中心组件，它负责整体的故障转移控制等。
它是一个守护进程，通过main()方法启动，继承自ZKFailoverController。 zkfc
使用JournalNode实现两个NameNode(Active和Standby)之间数据的共享
YARN-HA配置
YARN-HA工作机制
配置YARN-HA集群
yarn-site.xml
<property>
<name>yarn.nodemanager.aux-services</name>
<value>mapreduce_shuffle</value>
</property>
<!--启用resourcemanager ha-->
<property>
<name>yarn.resourcemanager.ha.enabled</name>
<value>true</value>
</property>
<!--声明两台resourcemanager的地址-->
<property>
<name>yarn.resourcemanager.cluster-id</name>
<value>cluster-yarn1</value>
</property>
<property>
<name>yarn.resourcemanager.ha.rm-ids</name>
<value>rm1,rm2</value>
</property>
<property>
<name>yarn.resourcemanager.hostname.rm1</name>
<value>hadoop101</value>
</property>
<property>
<name>yarn.resourcemanager.hostname.rm2</name>
<value>hadoop102</value>
</property>
<!--指定zookeeper集群的地址-->
<property>
<name>yarn.resourcemanager.zk-address</name>
<value>hadoop101:2181,hadoop102:2181,hadoop103:2181</value>
</property>
<!--启用自动恢复-->
<property>
<name>yarn.resourcemanager.recovery.enabled</name>
<value>true</value>
</property>
<!--指定resourcemanager的状态信息存储在zookeeper集群-->
<property>
<name>yarn.resourcemanager.store.class</name>
<value>org.apache.hadoop.yarn.server.resourcemanager.recovery.ZKRMStateStore</value>
</property>
http://hadoop101:8088/cluster