全网最详细的Hadoop HA集群启动后，两个namenode都是standby的解决办法（图文详解）

　　不多说，直接上干货！

解决办法

　　因为，如下，我的Hadoop HA集群。

1、首先在hdfs-site.xml中添加下面的参数，该参数的值默认为false：

  <property>
                <name>dfs.ha.automatic-failover.enabled.ns</name>
                <value>true</value>
        </property>

2、在core-site.xml文件中添加下面的参数，该参数的值为ZooKeeper服务器的地址，ZKFC将使用该地址。

　　在HA或者HDFS联盟中，上面的两个参数还需要以NameServiceID为后缀，比如dfs.ha.automatic-failover.enabled.mycluster。除了上面的两个参数外，还有其它几个参数用于自动故障转移，比如ha.zookeeper.session-timeout.ms，但对于大多数安装来说都不是必须的。

　　在添加了上述的配置参数后，下一步就是在ZooKeeper中初始化要求的状态，可以在任一NameNode中运行下面的命令实现该目的，该命在ZooKeeper中创建znode：

　　执行该命令需要进入Hadoop的安装目录下面的bin目录中找到hdfs这个命令，输入上面的命令执行，然后就可以修复这个问题了。

　　注意：之前，先得启动好，每台机器的zookeeper进程。

[kfk@bigdata-pro01 bin]$ pwd
/opt/modules/hadoop-2.6./bin
[kfk@bigdata-pro01 bin]$ ./hdfs zkfc -formatZK

// :: INFO zookeeper.ZooKeeper: Initiating client connection, connectString=bigdata-pro01.kfk.com:,bigdata-pro02.kfk.com:,bigdata-pro03.kfk.com: sessionTimeout= watcher=org.apache.hadoop.ha.ActiveStandbyElector$WatcherWithClientRef@20deea7f
// :: INFO zookeeper.ClientCnxn: Opening socket connection to server bigdata-pro01.kfk.com/192.168.80.151:. Will not attempt to authenticate using SASL (unknown error)
// :: INFO zookeeper.ClientCnxn: Socket connection established to bigdata-pro01.kfk.com/192.168.80.151:, initiating session
// :: INFO zookeeper.ClientCnxn: Session establishment complete on server bigdata-pro01.kfk.com/192.168.80.151:, sessionid = 0x164065bc2a90001, negotiated timeout =
===============================================
The configured parent znode /hadoop-ha/ns already exists.
Are you sure you want to clear all failover information from
ZooKeeper?
WARNING: Before proceeding, ensure that all HDFS services and
failover controllers are stopped!
===============================================
Proceed formatting /hadoop-ha/ns? (Y or N) // :: INFO ha.ActiveStandbyElector: Session connected.
y
// :: INFO ha.ActiveStandbyElector: Recursively deleting /hadoop-ha/ns from ZK...
// :: INFO ha.ActiveStandbyElector: Successfully deleted /hadoop-ha/ns from ZK.
// :: INFO ha.ActiveStandbyElector: Successfully created /hadoop-ha/ns in ZK.
// :: INFO zookeeper.ClientCnxn: EventThread shut down
// :: INFO zookeeper.ZooKeeper: Session: 0x164065bc2a90001 closed
[kfk@bigdata-pro01 bin]$ 

启动并测试

　　1、先停止掉Hadoop和zookeeper的进程。

　　2、启动zookeeper进程。

　　3、开启zkfc进程

[kfk@bigdata-pro01 hadoop-2.6.]$ pwd
/opt/modules/hadoop-2.6.
[kfk@bigdata-pro01 hadoop-2.6.]$ sbin/hadoop-daemon.sh start zkfc
starting zkfc, logging to /opt/modules/hadoop-2.6./logs/hadoop-kfk-zkfc-bigdata-pro01.kfk.com.out

　　4、进入Hadoop的安装目录下面的sbin目录中，找到start-dfs.sh命令可以启动NameNode，当然这里需要你在配置了NameNode主节点的Hadoop节点上面来执行他。

　　　　或者，直接sbin/start-all.sh

[kfk@bigdata-pro02 hadoop-2.6.]$ bin/hdfs -help
Usage: hdfs [--config confdir] COMMAND
       where COMMAND is one of:
  dfs                  run a filesystem command on the file systems supported in Hadoop.
  namenode -format     format the DFS filesystem
  secondarynamenode    run the DFS secondary namenode
  namenode             run the DFS namenode
  journalnode          run the DFS journalnode
  zkfc                 run the ZK Failover Controller daemon
  datanode             run a DFS datanode
  dfsadmin             run a DFS admin client
  haadmin              run a DFS HA admin client
  fsck                 run a DFS filesystem checking utility
  balancer             run a cluster balancing utility
  jmxget               get JMX exported values from NameNode or DataNode.
  mover                run a utility to move block replicas across
                       storage types
  oiv                  apply the offline fsimage viewer to an fsimage
  oiv_legacy           apply the offline fsimage viewer to an legacy fsimage
  oev                  apply the offline edits viewer to an edits file
  fetchdt              fetch a delegation token from the NameNode
  getconf              get config values from configuration
  groups               get the groups which users belong to
  snapshotDiff         diff two snapshots of a directory or diff the
                       current directory contents with a snapshot
  lsSnapshottableDir   list all snapshottable dirs owned by the current user
                        Use -help to see options
  portmap              run a portmap service
  nfs3                 run an NFS version  gateway
  cacheadmin           configure the HDFS cache
  crypto               configure HDFS encryption zones
  storagepolicies      get all the existing block storage policies
  version              print the version

Most commands print help when invoked w/o parameters.

[kfk@bigdata-pro02 hadoop-2.6.]$
[kfk@bigdata-pro02 hadoop-2.6.]$ bin/hdfs haadmin -help
Usage: DFSHAAdmin [-ns <nameserviceId>]
    [-transitionToActive <serviceId> [--forceactive]]
    [-transitionToStandby <serviceId>]
    [-failover [--forcefence] [--forceactive] <serviceId> <serviceId>]
    [-getServiceState <serviceId>]
    [-checkHealth <serviceId>]
    [-help <command>]

Generic options supported are
-conf <configuration file>     specify an application configuration file
-D <property=value>            use value for given property
-fs <local|namenode:port>      specify a namenode
-jt <local|resourcemanager:port>    specify a ResourceManager
-files <comma separated list of files>    specify comma separated files to be copied to the map reduce cluster
-libjars <comma separated list of jars>    specify comma separated jar files to include in the classpath.
-archives <comma separated list of archives>    specify comma separated archives to be unarchived on the compute machines.

The general command line syntax is
bin/hadoop command [genericOptions] [commandOptions]

[kfk@bigdata-pro02 hadoop-2.6.]$ 

　　　　注意，其实自带的命令里，都提供了，若两者都是standby状态怎么执行。若两者都是active状态怎么执行。这里，不多赘述。

　　如果，还是没解决的话，则

bin/hdfs haadmin -transitionToActive nn1

　

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