Introduction

Apache Hadoop is an open-source software framework that supports data-intensive distributed applications, licensed under the Apache v2 license. It supports the running of applications on large clusters of commodity hardware. Hadoop was derived from Google’s MapReduce and Google File System(GFS) papers.

Hadoop development needs a hadoop cluster.
A trial hadoop cluster can be setted up in minutes. In my previous blog post, I have mentioned about hadoop cluster set up using tarball.

But for production environments, tarball installation is not a good approach.
Because it will become complex while installing other hadoop ecosystem components.
If we have a high speed internet connection, we can install hadoop directly from the internet using yum install in minutes.
But most of the production environments are isolated. So internet connection may not be there.
There we can perform this yum install by creating a local yum repository.
Creation of local yum repository is explained well in my previous blog “Creating A Local YUM Repository”
Yum install will work with REDHAT or CentOS linux distributions.
Here I am giving the explanation of Cloudera Distribution of Hadoop installation.

Prerequisites

OPERATING SYSTEM

RedHat or CentOS (32 or 64 bit)

PORTS

The ports necessary for hadoop should be opened. So we need to set appropriate firewall rules. The ports used by hadoop are listed in the last part of this post.

If you are not interested in, you can simply switch off the firewall.

The command for turning off the firewall is

service iptables stop

JAVA

Sun java is required.

Download java from oracle website (32 or 64 bit depending on OS)

Install the java.

Simple installation and setting JAVA_HOME may not points the newly installed java as the default one.

It may still point to the openjdk if it is present.

So to point to the new java.

Do the following steps.

alternatives --config java

This will a list of java installed in the machine and to which java, it is currently pointing.

This will ask you to choose any java from the list.

Exit from this by pressing cntrl+c.

To add our sun java to this list. Do the following step.

/usr/sbin/alternatives --install /usr/bin/java java <JAVA_HOME>/bin/java 2

This will add our newly installed java to the list.

Then do

alternatives --config java

and choose the newly installed java. Now java –version will show sun java.

SETTING UP THE LOCAL HADOOP REPOSITORY

Download the Cloudera rpm repository from a place where you have internet access.

Download the repository corresponding to your OS version.
The repo file corresponding to different operating systems are listed below. Copy the repo file and download the repository.

For OS Version Click this Link
Red Hat/CentOS/Oracle 5 Red Hat/CentOS/Oracle 5
Red Hat/CentOS 6 (32-bit) Red Hat/CentOS/Oracle 6
Red Hat/CentOS 6 (64-bit) Red Hat/CentOS/Oracle 6

You can download it rpm by rpm or do a repo-sync.

Repo-sync is explained in my previous post Creating A Local YUM Repository.

Once this is done, create a local repository in one of the machines.

Then create a repo file corresponding to the newly created repository and add that repo file to all the cluster machines.

After this we can do yum install similar like a machine having internet access.

Now do a yum clean all in all the cluster machines.

Do the following steps in the corresponding nodes. The following steps explains the installation of MRV1 only.

Installation

NAMENODE MACHINE

yum install hadoop-hdfs-namenode

SECONDARY NAMENODE

yum install hadoop-hdfs-secondarynamenode

DATANODE

yum install hadoop-hdfs-datanode

JOBTRACKER

yum install hadoop-0.20-mapreduce-jobtracker

TASKTRACKER

yum install hadoop-0.20-mapreduce-tasktracker

IN ALL CLIENT MACHINES

yum install hadoop-client

Normally we run datanode and tasktracker in the same node. Ie these are co-located for data locality.

Now edit the core-site.xml, mapred-site.xml and hdfs-site.xml in all the machines.

Configurations

Sample configurations are given below.

But for production set up, you can set other properties.

core-site.xml


<configuration>
<property>
<name>hadoop.tmp.dir</name>
<value>/app/hadoop/tmp</value>
<description>A Base dir for storing other temp directories</description>
</property>

<property>
<name>fs.default.name</name>
<value>hdfs://<namenode-hostname>:9000</value>
<description>The name of default file system</description>
</property>
</configuration>

mapred-site.xml

<configuration>
<property>
<name>mapred.job.tracker</name>
<value><jobtracker-hostname>:9001</value>
<description>Job Tracker port</description>
</property>

<property>
<name>mapred.local.dir</name>
<value>/app/hadoop/mapred_local</value>
<description>local dir for mapreduce jobs</description>
</property>


<property>
  <name>mapred.tasktracker.map.tasks.maximum</name>
  <value>6</value>
  <description>The maximum number of map tasks that will be run
  simultaneously by a task tracker.
  </description>
</property>
<property>
  <name>mapred.tasktracker.reduce.tasks.maximum</name>
  <value>2</value>
  <description>The maximum number of reduce tasks that will be run
  simultaneously by a task tracker.
  </description>
</property>
</configuration>

hdfs-site.xml

<configuration>
<property>
<name>dfs.replication</name>
<value>3</value>
<description>replication factor</description>
</property>
</configuration>

Then create hadoop.tmp.dir in all the machines. Hadoop stores its files in this folder.

Here we are using the location /app/hadoop/tmp

mkdir –p /app/hadoop/tmp

mkdir /app/hadoop/mapred_local

This type of installation automatically creates two users

1) hdfs

2) mapred

The directories should be owned by hdfs, so we need to change the ownership

chown –R hdfs:hadoop /app/hadoop/tmp

chmod –R 777 /app/hadoop/tmp

chown mapred:hadoop /app/hadoop/mapred_local

The properties

mapred.tasktracker.map.tasks.maximum :- this will set the number of map slots in each node.

mapred.tasktracker.reduce.tasks.maximum :- this will set the number of reduce slots in each node.

This number is set by doing a calculation on the available RAM and jvm size of each task slot. The default size of the task slot is 200 MB. So if you have 4GB RAM free after sharing to OS requirements and other processes. We can have 4*1024 MB/200 number of task slots in that node.

ie 4*1024/200 = 20

So we can have 20 task slots which we can divide into map slots and reduce slots.
Usually we give higher number of map slots than reduce slots.
In hdfs-site.xml we are giving the replication factor. Default value is 3.

Formatting Namenode

Now go to the namenode machine and login as root user.

Then from cli, switch to hdfs user.

su – hdfs

Then format the namenode.

hadoop namenode –format

Starting Services

STARTING NAMENODE

In the namenode machine, execute the following command as root user.

/etc/init.d/hadoop-hdfs-namenode start

You can check whether the service is running or not by using the command jps.

Jps will work only if sun java is installed and added to path.

STARTING SECONDARY NAMENODE

In the Secondary Namenode machine, execute the following command as root user.

/etc/init.d/hadoop-hdfs-secondarynamenode start

STARTING DATANODE

In the Datanode machines, execute the following command as root user.

/etc/init.d/hadoop-hdfs-datanode start

Now the hdfs is started. Now we will be able to execute hdfs tasks.

STARTING JOBTRACKER

In the jobtracker machine login as root user, then switch to hdfs user.

su – hdfs

Then create the following hdfs directory structure and permissions.

hadoop fs –mkdir /app

hadoop fs –mkdir /app/hadoop

hadoop fs –mkdir /app/hadoop/tmp

hadoop fs –mkdir /app/hadoop/tmp/mapred

hadoop fs –mkdir /app/hadoop/tmp/mapred/staging

hadoop fs –chmod –R 1777 /app/hadoop/tmp/mapred/staging

hadoop fs –chown mapred:hadoop /app/hadoop/tmp/mapred

After doing this start the jobtracker

/etc/init.d/hadoop-0.20-mapreduce-jobtracker start

STARTING TASKTRACKER

In the tasktracker nodes, start the tasktracker by executing the following command

/etc/init.d/hadoop-0.20-mapreduce-tasktracker start

You can check the namenode webUI using a browser.

The URL is

http://<namenode-hostname>:50070

The Jobtracker web UI is

http://<jobtracker-hostname>:50030

If hostname resolution is not happened correctly, the hostname:port may not work.

In these situtaions you can use http://ip-address:port

Now our hadoop cluster is ready for use.

With this method, we can create hadoop cluster of any size within short time.

Here we have the entire hadoop ecosystem repository, so installing other components such as hive, pig, Hbase, sqoop etc can be done very easily.

Ports Used By Hadoop

blogports