Tuesday, August 23, 2016

Hadoop - How to setup a Hadoop Cluster

Below is a step-by-step guide which I had used to setup a Hadoop Cluster

Scenario


3 VMs involved:

1) NameNode, ResourceManager - Host name: NameNode.net
2) DataNode 1 - Host name: DataNode1.net
3) DataNode 2 - Host name: DataNode2.net


Pre-requisite


1) You could create a new Hadoop user or use an existing user. But make sure the user have access to the Hadoop installation in ALL nodes

2) Install JAVA. Refer here for a good version. In this guide, Java is installed at /usr/java/latest

3) Download a stable version of Hadoop from Apache Mirrors

This guide is based on Hadoop 2.7.1 and assume that we had create a user call hadoop


Setup Passphaseless SSH from NameNode to all Nodes.


1) Run the command

ssh-keygen

This command will ask you a set of questions and accepting the default is fine. Eventually, it will create a set of private key (id_rsa) and public key (id_rsa.pub) at the user directory (/home/hadoop/.ssh)

2) Copy the public key to all Nodes with the following

ssh-copy-id -i /home/hadoop/.ssh/id_rsa.pub NameNode.net
ssh-copy-id -i /home/hadoop/.ssh/id_rsa.pub DataNode1.net
ssh-copy-id -i /home/hadoop/.ssh/id_rsa.pub DataNode2.net

3) Test the passphaseless SSH connection from NameNode with

ssh (hostname)


Install Hadoop in all Node


1) With the downloaded Hadoop distribution. Unzip it to a location where the Hadoop user had access

For this guide, I had create a /usr/local/hadoop and un-tar the distribution at this folder. The full path of Hadoop installation is /usr/local/hadoop/hadoop-2.7.1


Setup Environment Variables


1) It is best that Hadoop Variables are exported to the environment when user log in. To do so, run the command at the NameNode

sudo vi /etc/profile.d/hadoop.sh

2) Add the following in /etc/profile.d/hadoop.sh

export JAVA_HOME=/usr/java/latest
export HADOOP_HOME=/usr/hadoop
export HADOOP_COMMON_HOME=$HADOOP_HOME
export HADOOP_HDFS_HOME=$HADOOP_HOME
export HADOOP_MAPRED_HOME=$HADOOP_HOME
export HADOOP_YARN_HOME=$HADOOP_HOME
export HADOOP_OPTS="-Djava.library.path=$HADOOP_HOME/lib/native"
export HADOOP_COMMON_LIB_NATIVE_DIR=$HADOOP_HOME/lib/native
export PATH=$HADOOP_HOME/sbin:$HADOOP_HOME/bin:$JAVA_HOME/bin:$PATH
3) Source this file or re-login to setup the environment.

4) (OPTIONAL) Set up the above for all Nodes.


Setup NameNode & ResourceManager


1) Make a directory to hold NameNode data

mkdir /usr/local/hadoop/hdfs_namenode

2) Setup $HADOOP_HOME/etc/hadoop/hdfs-site.xml




Note: dfs.datanode.data.dir value must be a URI

3) Setup $HADOOP_HOME/etc/hadoop/core-site.xml





4) (OPTIONAL) Setup $HADOOP_HOME/etc/hadoop/mapred-site.xml (We are using NameNode as ResourceManager)



5) (OPTIONAL) Setup $HADOOP_HOME/etc/hadoop/yarn-site.xml (We are using NameNode as ResourceManager)


6) Setup $HADOOP_HOME/etc/hadoop/slaves

First, remove localhost from the file, then add the following



Setup DataNodes


1) Make a directory to hold DataNode data

mkdir /usr/local/hadoop/hdfs_datanode

2) Setup $HADOOP_HOME/etc/hadoop/hdfs-site.xml



Note: dfs.datanode.data.dir value must be a URI

3) Setup $HADOOP_HOME/etc/hadoop/core-site.xml




Format NameNode


The above setting should be enough to set up the Hadoop cluster. Next, for the first time, you will need to format the NameNode. Use the following command to format the NameNode

hdfs namenode -format

Example output is



Note: the same command can be used to reformat your existing NameNode. But remember to clean up your datanodes hdfs folder as well.


Start NameNode


You can start Hadoop with the given script

start-dfs.sh

Example output is










Stop NameNode


You can stop Hadoop with the given script

stop-dfs.sh

Example output is



Start ResourceManager


You can start the ResourceManager, in this case, Yarn, with the given script

start-yarn.sh

Example output is




Stop ResourceManager


You can stop the ResourceManager, in this case, Yarn, with the given script

stop-yarn.sh

Example output is



Show status of Hadoop


You can use the following command to show status of Hadoop

jps

Example output is











Complete Testing


You can also do the following to perform a complete test to ensure Hadoop is running fine.






















You could access the Hadoop Resource Manager information at http://NameNode_hostname:8088



You could also access the Hadoop cluster summary at http://NameNode_hostname:50070. You should be able to see the number of datanodes being setup for the cluster.


Reference


1. http://www.server-world.info/en/note?os=CentOS_7&p=hadoop
2. http://hadoop.apache.org/docs/current/hadoop-project-dist/hadoop-common/ClusterSetup.html


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