Hadoop集群节点的动态增加
1. 安装配置节点
具体过程参考 《Hadoop集群实践 之 (1) Hadoop(HDFS)搭建》
2. 在配置过程中需要在所有的Hadoop服务器上更新以下三项配置
$ sudo vim /etc/hadoop/conf/slaves
$ sudo vim /etc/hosts
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10.6.1.150
hadoop-master
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10.6.1.151
hadoop-node-1
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10.6.1.152
hadoop-node-2
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4
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10.6.1.153
hadoop-node-3
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$ sudo vim /etc/hadoop/conf/hdfs-site.xml
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<?xml-stylesheet type="text/xsl" href="configuration.xsl"?>
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<name>dfs.data.dir</name>
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<value>/data/hdfs</value>
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<name>dfs.replication</name>
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<name>dfs.datanode.max.xcievers</name>
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3. 启动datanode与tasktracker
[email protected]:~$ sudo /etc/init.d/hadoop-0.20-datanode start
[email protected]:~$ sudo /etc/init.d/hadoop-0.20-tasktracker start
4. 检查新增节点是否已经Live
通过WEB管理界面查看
http://10.6.1.150:50070/dfsnodelist.jsp?whatNodes=LIVE
可以看到hadoop-node-3已经被动态添加到了Hadoop集群中
5.应用新的备份系数dfs.replication
5.1 检查目前的备份系数
[email protected]:~$ sudo -u hdfs hadoop fs -lsr /dongguo
-rw-r--r-- 2 hdfs supergroup 33 2012-10-07 22:02 /dongguo/hello.txt
结果行中的第2列是备份系数（注：文件夹信息存储在namenode节点上，没有备份，故文件夹的备份系数是横杠-）
目前文件的备份系数仍是之前设置的参数2，Hadoop不会自动的按照新的备份系数进行调整。
[email protected]:~$ sudo -u hdfs hadoop fsck /
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12/10/10
21:18:32 INFO security.UserGroupInformation: JAAS Configuration already setup for Hadoop,
not re-installing.
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FSCK
started by hdfs (auth:SIMPLE) from /10.6.1.150 for path
/ at Wed Oct 10 21:18:33 CST 2012
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.................Status:
HEALTHY
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Total
blocks (validated): 17 (avg. block size 458 B)
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08
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Minimally
replicated blocks: 17 (100.0 %)
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Over-replicated
blocks: 0 (0.0 %)
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Under-replicated
blocks: 0 (0.0 %)
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Mis-replicated
blocks: 0 (0.0 %)
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Default
replication factor: 2
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Average
block replication: 2.0
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Missing
replicas: 0 (0.0 %)
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Number
of data-nodes: 4
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FSCK
ended at Wed Oct 10 21:18:33 CST 2012 in 48
milliseconds
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The
filesystem under path '/' is
HEALTHY
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通过 hadoop fsck / 也可以方便的看到Average block replication的值仍然为旧值2，该值我们可以手动的进行动态修改。
而Default replication factor则需要重启整个Hadoop集群才能修改，但实际影响系统的还是Average block replication的值，因此并非一定要修改默认值。
5.2 修改hdfs文件备份系数，把/ 目录下所有文件备份系数设置为3
[email protected]:~$ sudo -u hdfs hadoop dfs -setrep -w 3 -R /
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12/10/10
21:22:35 INFO security.UserGroupInformation: JAAS Configuration already setup for Hadoop,
not re-installing.
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可以看到Hadoop对所有文件的备份系数进行了刷新
5.3 再次检查备份系数的情况
[email protected]:~$ sudo -u hdfs hadoop fsck /
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12/10/10
21:23:26 INFO security.UserGroupInformation: JAAS Configuration already setup for Hadoop,
not re-installing.
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FSCK
started by hdfs (auth:SIMPLE) from /10.6.1.150 for path
/ at Wed Oct 10 21:23:27 CST 2012
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03
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.................Status:
HEALTHY
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07
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Total
blocks (validated): 17 (avg. block size 458 B)
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08
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Minimally
replicated blocks: 17 (100.0 %)
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09
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Over-replicated
blocks: 0 (0.0 %)
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Under-replicated
blocks: 0 (0.0 %)
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Mis-replicated
blocks: 0 (0.0 %)
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Default
replication factor: 2
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Average
block replication: 3.0
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Missing
replicas: 0 (0.0 %)
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Number
of data-nodes: 4
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FSCK
ended at Wed Oct 10 21:23:27 CST 2012 in 11
milliseconds
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The
filesystem under path '/' is
HEALTHY
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可以看到已经变成了新的备份系数"3"
5.4 测试一下创建新的文件时是否能集成新的备份系数
[email protected]:~$ sudo -u hdfs hadoop fs -copyFromLocal mysql-connector-java-5.1.22.tar.gz /dongguo
[email protected]:~$ sudo -u hdfs hadoop fs -lsr /dongguo
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-rw-r--r--
3 hdfs supergroup 33 2012-10-07 22:02 /dongguo/hello.txt
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-rw-r--r--
3 hdfs supergroup 4028047 2012-10-10 21:28 /dongguo/mysql-connector-java-5.1.22.tar.gz
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可以看到新上传的文件的备份系数是"3"
6 对HDFS中的文件进行负载均衡
[email protected]:~$ sudo -u hdfs hadoop balancer
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Time
Stamp Iteration#
Bytes Already Moved Bytes Left To Move Bytes Being Moved
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12/10/10
21:30:25 INFO net.NetworkTopology: Adding a new node: /default-rack/10.6.1.153:50010
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12/10/10
21:30:25 INFO net.NetworkTopology: Adding a new node: /default-rack/10.6.1.150:50010
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12/10/10
21:30:25 INFO net.NetworkTopology: Adding a new node: /default-rack/10.6.1.152:50010
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12/10/10
21:30:25 INFO net.NetworkTopology: Adding a new node: /default-rack/10.6.1.151:50010
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12/10/10
21:30:25 INFO balancer.Balancer: 0 over utilized nodes:
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12/10/10
21:30:25 INFO balancer.Balancer: 0 under utilized nodes:
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The
cluster is balanced. Exiting...
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Balancing
took 1.006 seconds
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至此，Hadoop集群的动态增加就已经完成了。
下面，我开始对Hadoop集群的节点进行动态的删除。
Hadoop集群节点的动态删除
1. 使用新增的节点
尽可能的在HDFS中产生一些测试数据，并通过Hive执行一些Job以便使新的节点也执行MapReduce并行计算。
这样做的原因是尽可能的模拟线上的环境，因为线上环境在进行删除节点之前肯定是有很多数据和Job执行过的。
2. 修改core-site.xml
[email protected]:~$ sudo vim /etc/hadoop/conf/core-site.xml
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<name>dfs.hosts.exclude</name>
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<value>/etc/hadoop/conf/exclude</value>
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<description>Names
a file that contains a list of hosts that are
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not
permitted to connect to the namenode. The full pathname of the
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file
must be specified. If the value is empty, no hosts are
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excluded.</description>
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3. 修改hdfs-site.xml
[email protected]:~$ sudo vim /etc/hadoop/conf/hdfs-site.xml
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<name>dfs.hosts.exclude</name>
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<value>/etc/hadoop/conf/exclude</value>
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<description>Names
a file that contains a list of hosts that are
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not
permitted to connect to the namenode. The full pathname of the
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file
must be specified. If the value is empty, no hosts are
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excluded.</description>
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4. 创建/etc/hadoop/conf/exclude
[email protected]:~$ sudo vim /etc/hadoop/conf/exclude
在文件中增加需要删除的节点，一行一个，我这里仅需要写入新增的hadoop-node-3做测试。
5. 降低备份系数
在我的测试环境中，目前节点为4台，备份系数为3，如果去掉一台的话备份系数就与节点数相同了，而Hadoop是不允许的。
通常备份系数不需要太高，可以是服务器总量的1/3左右即可，Hadoop默认的数值是3。
下面，我们将备份系数从3降低到2
5.1 在所有的Hadoop服务器上更新以下配置
$ sudo vim /etc/hadoop/conf/hdfs-site.xml
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<?xml-stylesheet type="text/xsl" href="configuration.xsl"?>
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<name>dfs.data.dir</name>
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<value>/data/hdfs</value>
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<name>dfs.replication</name>
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<name>dfs.datanode.max.xcievers</name>
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5.2 修改hdfs文件备份系数，把/ 目录下所有文件备份系数设置为2
[email protected]:~$ sudo -u hdfs hadoop dfs -setrep -w 2 -R /
遇到的疑问：
在进行文件备份系数的降低时，能够很快的进行Replication set，但是在Waiting for的过程中却很长时间没有完成。
最终只能手动Ctrl+C中断，个人猜测在这个过程中HDFS正视图对数据文件进行操作，在删除一个副本容量的数据。
因此，我们应该对dfs.replication的数值做出很好的规划，尽量避免需要降低该数值的情况出现。
6. 动态刷新配置
[email protected]:~$ sudo -u hdfs hadoop dfsadmin -refreshNodes
7. 检查节点的处理状态
通过WEB管理界面查看
Decommissioning(退役中)
http://10.6.1.150:50070/dfsnodelist.jsp?whatNodes=DECOMMISSIONING
Dead(已经下线)
http://10.6.1.150:50070/dfsnodelist.jsp?whatNodes=DEAD
可以看到，节点已经经历了退役的过程并成功的下线了。
需要注意的是：
在删除节点时一定要停止所有Hadoop的Job，否则程序还会向要删除的节点同步数据，这样也会导致Decommission的过程一直无法完成。
8. 检查进程状态
这时我们查看进程状态，可以发现datanode进程已经被自动中止了
[email protected]:~$ sudo /etc/init.d/hadoop-0.20-datanode status
hadoop-0.20-datanode is not running.
而Tasktracker进程还在，需要我们手动中止
[email protected]:~$ sudo /etc/init.d/hadoop-0.20-tasktracker status
hadoop-0.20-tasktracker is running
[email protected]:~$ sudo /etc/init.d/hadoop-0.20-tasktracker stop
Stopping Hadoop tasktracker daemon: stopping tasktracker
hadoop-0.20-tasktracker.
此时，即使我们手动启动datanode，也是不能成功的，日志中会显示UnregisteredDatanodeException的错误。
[email protected]:~$ sudo /etc/init.d/hadoop-0.20-datanode start
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Starting
Hadoop datanode daemon: starting datanode, logging to /usr/lib/hadoop-0.20/logs/hadoop-hadoop-datanode-hadoop-node-3.out
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ERROR.
Could not start Hadoop datanode daemon
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[email protected]:~$ tailf /var/log/hadoop/hadoop-hadoop-datanode-hadoop-node-3.log
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2012-10-11
19:33:22,084 ERROR org.apache.hadoop.hdfs.server.datanode.DataNode: org.apache.hadoop.ipc.RemoteException: org.apache.hadoop.hdfs.protocol.UnregisteredDatanodeException: Data node hadoop-node-3:50010 is attempting to report storage ID DS-500645823-10.6.1.153-50010-1349941031723.
Node 10.6.1.153:50010 is expected to serve this storage.
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at
org.apache.hadoop.hdfs.server.namenode.FSNamesystem.getDatanode(FSNamesystem.java:4547)
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at
org.apache.hadoop.hdfs.server.namenode.FSNamesystem.verifyNodeRegistration(FSNamesystem.java:4512)
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at
org.apache.hadoop.hdfs.server.namenode.FSNamesystem.registerDatanode(FSNamesystem.java:2355)
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at
org.apache.hadoop.hdfs.server.namenode.NameNode.register(NameNode.java:932)
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at
sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
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at
sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
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at
sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
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at
java.lang.reflect.Method.invoke(Method.java:597)
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at
org.apache.hadoop.ipc.RPC$Server.call(RPC.java:557)
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at
org.apache.hadoop.ipc.Server$Handler$1.run(Server.java:1434)
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at
org.apache.hadoop.ipc.Server$Handler$1.run(Server.java:1430)
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at
java.security.AccessController.doPrivileged(Native Method)
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at
javax.security.auth.Subject.doAs(Subject.java:396)
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15
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at
org.apache.hadoop.security.UserGroupInformation.doAs(UserGroupInformation.java:1157)
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at
org.apache.hadoop.ipc.Server$Handler.run(Server.java:1428)
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at
org.apache.hadoop.ipc.Client.call(Client.java:1107)
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at
org.apache.hadoop.ipc.RPC$Invoker.invoke(RPC.java:226)
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19
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at
$Proxy4.register(Unknown Source)
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at
org.apache.hadoop.hdfs.server.datanode.DataNode.register(DataNode.java:717)
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at
org.apache.hadoop.hdfs.server.datanode.DataNode.runDatanodeDaemon(DataNode.java:1519)
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22
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at
org.apache.hadoop.hdfs.server.datanode.DataNode.createDataNode(DataNode.java:1586)
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at
org.apache.hadoop.hdfs.server.datanode.DataNode.secureMain(DataNode.java:1711)
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at
org.apache.hadoop.hdfs.server.datanode.DataNode.main(DataNode.java:1728)
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2012-10-11
19:33:22,097 INFO org.apache.hadoop.hdfs.server.datanode.DataNode: SHUTDOWN_MSG:
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/************************************************************
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SHUTDOWN_MSG:
Shutting down DataNode at hadoop-node-3/10.6.1.153
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************************************************************/
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至此，对Hadoop集群节点的动态删除也已经成功完成了。
