Setting Up A Hadoop Multi-Node Cluster
Installing Java
First, the Installation of java is important to set up a Multi-node cluster.
Syntax of java version command
$ java -version
Following output is presented.
java version "1.7.0_71"
Java(TM) SE Runtime Environment (build 1.7.0_71-b13)
Java HotSpot(TM) Client VM (build 25.0-b02, mixed mode)
Creating User Account
System user account on both master and slave systems should be created to use the Hadoop installation.
# useradd hadoop
# passwd hadoop
Mapping the nodes
hosts file should be edited in /etc/ folder on all nodes and IP address of each system followed by their host names must be specified.
# vi /etc/hosts
Enter the following lines in the /etc/hosts file.
192.168.1.109 hadoop-master
192.168.1.145 hadoop-slave-1
192.168.56.1 hadoop-slave-2
Configuring Key Based Login
Ssh should be setup in each node such that they can converse with one another without any prompt for a password.
# su hadoop
$ ssh-keygen -t rsa
$ ssh-copy-id -i ~/.ssh/id_rsa.pub tutorialspoint@hadoop-master
$ ssh-copy-id -i ~/.ssh/id_rsa.pub hadoop_tp1@hadoop-slave-1
$ ssh-copy-id -i ~/.ssh/id_rsa.pub hadoop_tp2@hadoop-slave-2
$ chmod 0600 ~/.ssh/authorized_keys
$ exit
Learn more about Hadoop with the help of this YouTube tutorial:
Installing Hadoop
Hadoop should be downloaded to the master server.
# mkdir /opt/hadoop
# cd /opt/hadoop/
# wget http://apache.mesi.com.ar/hadoop/common/hadoop-1.2.1/hadoop-1.2.0.tar.gz
# tar -xzf hadoop-1.2.0.tar.gz
# mv hadoop-1.2.0 hadoop
# chown -R hadoop /opt/hadoop
# cd /opt/hadoop/hadoop/
Configuring Hadoop
Hadoop server must be configured
core-site.xml should be edited.
<configuration>
<property>
<name>fs.default.name</name><value>hdfs://hadoop-master:9000/</value>
</property>
<property>
<name>dfs.permissions</name>
<value>false</value>
</property>
</configuration>
hdfs-site.xml file should be edited.
<configuration>
<property>
<name>dfs.data.dir</name>
<value>/opt/hadoop/hadoop/dfs/name/data</value>
<final>true</final>
</property>
<property>
<name>dfs.name.dir</name>
<value>/opt/hadoop/hadoop/dfs/name</value>
<final>true</final>
</property>
<property>
<name>dfs.replication</name>
<value>1</value>
</property>
</configuration>
mapred-site.xml file should be edited.
<configuration>
<property>
<name>mapred.job.tracker</name><value>hadoop-master:9001</value>
</property>
</configuration>
JAVA_HOME, HADOOP_CONF_DIR, and HADOOP_OPTS should be edited.
export JAVA_HOME=/opt/jdk1.7.0_17
export HADOOP_OPTS=-Djava.net.preferIPv4Stack=true
export HADOOP_CONF_DIR=/opt/hadoop/hadoop/conf
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Installing Hadoop on Slave Servers
Hadoop should be installed on all the slave servers
# su hadoop
$ cd /opt/hadoop
$ scp -r hadoop hadoop-slave-1:/opt/hadoop
$ scp -r hadoop hadoop-slave-2:/opt/hadoop
Configuring Hadoop on Master Server
The master server should be configured
# su hadoop
$ cd /opt/hadoop/hadoop
Master Node Configuration
$ vi etc/hadoop/masters
hadoop-master
Slave Node Configuration
$ vi etc/hadoop/slaves
hadoop-slave-1
hadoop-slave-2
Name Node format on Hadoop Master
# su hadoop
$ cd /opt/hadoop/hadoop
$ bin/hadoop namenode –format
11/10/14 10:58:07 INFO namenode.NameNode: STARTUP_MSG:
/************************************************************
STARTUP_MSG: Starting NameNode
STARTUP_MSG: host = hadoop-master/192.168.1.109
STARTUP_MSG: args = [-format]
STARTUP_MSG: version = 1.2.0
STARTUP_MSG: build =
https://svn.apache.org/repos/asf/hadoop/common/branches/branch-1.2 -r 1479473; compiled by 'hortonfo' on Mon May 6 06:59:37 UTC 2013
STARTUP_MSG: java = 1.7.0_71
************************************************************/
11/10/14 10:58:08 INFO util.GSet: Computing capacity for map BlocksMap editlog=/opt/hadoop/hadoop/dfs/name/current/edits
………………………………………………….
………………………………………………….
………………………………………………….
11/10/14 10:58:08 INFO common.Storage: Storage directory /opt/hadoop/hadoop/dfs/name has been successfully formatted.
11/10/14 10:58:08 INFO namenode.NameNode: SHUTDOWN_MSG: /************************************************************
SHUTDOWN_MSG: Shutting down NameNode at hadoop-master/192.168.1.15
************************************************************/
Hadoop Services
Starting Hadoop services on the Hadoop-Master.
$ cd $HADOOP_HOME/sbin
$ start-all.sh
Addition of a New DataNode in the Hadoop Cluster
Networking
Add new nodes to an existing Hadoop cluster with some suitable network configuration. suppose the following network configuration.
For New node Configuration:
IP address : 192.168.1.103
netmask : 255.255.255.0
hostname : slave3.in
Adding a User and SSH Access
Add a User
“hadoop” user must be added and password of Hadoop user can be set to anything one wants.
useradd hadoop
passwd hadoop
To be executed on master
mkdir -p $HOME/.ssh
chmod 700 $HOME/.ssh
ssh-keygen -t rsa -P '' -f $HOME/.ssh/id_rsa
cat $HOME/.ssh/id_rsa.pub >> $HOME/.ssh/authorized_keys
chmod 644 $HOME/.ssh/authorized_keys
Copy the public key to new slave node in hadoop user $HOME directory
scp $HOME/.ssh/id_rsa.pub [email protected]:/home/hadoop/
To be executed on slaves
su hadoop ssh -X [email protected]
Content of public key must be copied into file “$HOME/.ssh/authorized_keys” and then the permission for the same must be changed.
cd $HOME
mkdir -p $HOME/.ssh
chmod 700 $HOME/.ssh
cat id_rsa.pub >>$HOME/.ssh/authorized_keys
chmod 644 $HOME/.ssh/authorized_keys
ssh login must be changed from the master machine. The possibility of ssh to the new node without a password from the master must be verified.
ssh [email protected] or hadoop@slave3
Set Hostname of New Node
Hostname is set in file /etc/sysconfig/network
On new slave3 machine
NETWORKING=yes
HOSTNAME=slave3.in
The machine must be restarted or hostname command should be run to a new machine with the respective hostname to make changes effective.
On slave3 node machine:
hostname slave3.in
/etc/hosts must be updated on all machines of the cluster
192.168.1.102 slave3.in slave3
ping the machine with hostnames to check whether it is resolving to IP.
ping master.in
Start the DataNode on New Node
Datanode daemon should be started manually using $HADOOP_HOME/bin/hadoop-daemon.sh script. Master(NameNode) should join the cluster after being automatically contacted. A new node should be added to the conf/slaves file in the master server. A new node will be recognized by script-based commands.
Login to new node
su hadoop or ssh -X [email protected]
HDFS is started on a newly added slave node
./bin/hadoop-daemon.sh start datanode
jps command output must be checked on a new node.
$ jps
7141 DataNode
10312 Jps
Removing a DataNode
Node can be removed from a cluster as it is running, without any data loss. A decommissioning feature is made available by HDFS which ensures that removing a node is performed securely.
Step 1
Login to master machine user where Hadoop is installed.
$ su hadoop
Step 2
Before starting the cluster an exclude file must be configured. A key named dfs.hosts.exclude should be added to our $HADOOP_HOME/etc/hadoop/hdfs-site.xmlfile.
NameNode’s local file system which contains a list of machines that are not permitted to connect to HDFS receives the full path by this key and the value associated with it.
<property>
<name>dfs.hosts.exclude</name><value>/home/hadoop/hadoop-1.2.1/hdfs_exclude.txt</value><description>>DFS exclude</description>
</property>
Step 3
Hosts to decommission are determined.
Additions should be made to file recognized by the hdfs_exclude.txt for every machine to be decommissioned which will prevent them from connecting to the NameNode.
slave2.in
Step 4
Force configuration reload.
“$HADOOP_HOME/bin/hadoop dfsadmin -refreshNodes” should be run
$ $HADOOP_HOME/bin/hadoop dfsadmin -refreshNodes
NameNode will be forced to re-read its configuration, this is inclusive of the newly updated ‘excludes’ file. Nodes will be decommissioned over a period of time, allowing time for each node’s blocks to be replicated onto machines that are scheduled to remain active.
jps command output should be checked on slave2.in. DataNode process will shut down automatically.
Step 5
Shutdown nodes.
The decommissioned hardware can be carefully shut down for maintenance after the decommission process has been finished.
$ $HADOOP_HOME/bin/hadoop dfsadmin -report
Step 6
Excludes are edited again and once the machines have been decommissioned, they can be removed from the ‘excludes’ file. “$HADOOP_HOME/bin/hadoop dfsadmin -refreshNodes” will read the excluded file back into the NameNode; DataNodes will rejoin the cluster after the maintenance has been completed, or if additional capacity is needed in the cluster again.
To run/shutdown tasktracker
$ $HADOOP_HOME/bin/hadoop-daemon.sh stop tasktracker
$ $HADOOP_HOME/bin/hadoop-daemon.sh start tasktracker