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Hadoop
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Last updated: 2025-01-24 13:06:55
Hadoop
Last updated: 2025-01-24 13:06:55
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Hadoop (2.7.2 or above) tool provides the capability to run computing tasks using Tencent Cloud COS as the underlying file storage system. The Hadoop cluster can be launched in three modes: stand-alone, pseudo-distributed, and fully-distributed. This document uses Hadoop-2.7.4 as an example to describe how to build a fully-distributed Hadoop environment and how to use wordcount to execute a simple test.

Preparation

Prepare several servers.
Install and configure the system by downloading from the CentOS Official Website. This document uses CentOS 7.3.1611.
Install the Java environment. For more information, see Installing and Configuring Java.
Install the available Hadoop package: Apache Hadoop Releases Download.

Network Configuration

Use ifconfig -a to check the IP of each server, then use the ping command to check if they can ping each other, and record the IP of each server.

Configuring CentOS

Configure a Hostname

Set the corresponding hostname for each machine, such as "master", "slave*", etc.
hostnamectl set-hostname master

Configure hosts

vi /etc/hosts
Edit the content:
202.xxx.xxx.xxx master
202.xxx.xxx.xxx slave1
202.xxx.xxx.xxx slave2
202.xxx.xxx.xxx slave3
# Replace IPs with the real ones

Turn off firewall

systemctl status firewalld.service  # Check firewall status
systemctl stop firewalld.service  # Turn off firewall
systemctl disable firewalld.service  # Disable firewall to start on boot

Time synchronization

yum install -y ntp  # Install ntp service
ntpdate cn.pool.ntp.org  # Sync network time

Install and configure JDK

Upload JDK installer package (such as jdk-8u144-linux-x64.tar.gz) to the root directory.
mkdir /usr/java
tar -zxvf jdk-8u144-linux-x64.tar.gz -C /usr/java/
rm -rf jdk-8u144-linux-x64.tar.gz

Copy JDKs among hosts

scp -r /usr/java slave1:/usr
scp -r /usr/java slave2:/usr
scp -r /usr/java slave3:/usr
.......

Configure environment variables for JDK of each host

vi /etc/profile
Edit the content:
export JAVA_HOME=/usr/java/jdk1.8.0_144
export PATH=$JAVA_HOME/bin:$PATH
export CLASSPATH=.:$JAVA_HOME/lib/dt.jar:$JAVA_HOME/lib/tools.jar
After saving the file, make /etc/profile take effect by executing the following command:
source /etc/profile   # Make the configuration file effective
java -version          # View java version

Configuring Keyless Access via SSH

Check the SSH service status on each host:
systemctl status sshd.service  # Check the SSH service status.
yum install openssh-server openssh-clients  # Install the SSH service. Ignore this step if it is already installed.
systemctl start sshd.service  # Enable the SSH service. Ignore this step if it is already enabled.
Generate a key on each host:
ssh-keygen -t rsa  # Generate Keys
On slave1:
cp ~/.ssh/id_rsa.pub ~/.ssh/slave1.id_rsa.pub
scp ~/.ssh/slave1.id_rsa.pub master:~/.ssh
On slave2:
cp ~/.ssh/id_rsa.pub ~/.ssh/slave2.id_rsa.pub
scp ~/.ssh/slave2.id_rsa.pub master:~/.ssh
And so on...
On master:
cd ~/.ssh
cat id_rsa.pub >> authorized_keys
cat slave1.id_rsa.pub >>authorized_keys
cat slave2.id_rsa.pub >>authorized_keys
scp authorized_keys slave1:~/.ssh
scp authorized_keys slave2:~/.ssh
scp authorized_keys slave3:~/.ssh

Installing and Configuring Hadoop

Installing Hadoop

Upload the Hadoop installer package (such as hadoop-2.7.4.tar.gz) to the root directory.
tar -zxvf hadoop-2.7.4.tar.gz -C /usr
rm -rf hadoop-2.7.4.tar.gz
mkdir /usr/hadoop-2.7.4/tmp
mkdir /usr/hadoop-2.7.4/logs
mkdir /usr/hadoop-2.7.4/hdf
mkdir /usr/hadoop-2.7.4/hdf/data
mkdir /usr/hadoop-2.7.4/hdf/name
Go to the hadoop-2.7.4/etc/hadoop directory and proceed to the next step.

Configure Hadoop

1. Add the following to the hadoop-env.sh file.
export JAVA_HOME=/usr/java/jdk1.8.0_144
If the SSH port is not 22 (default value), modify it in the hadoop-env.sh file:
export HADOOP_SSH_OPTS="-p 1234"
2. Modify yarn-env.sh
export JAVA_HOME=/usr/java/jdk1.8.0_144
3. Modify slaves
Configure the content:
Delete:
localhost
Add:
slave1
slave2
slave3
4. Modify core-site.xml
<configuration>
  <property>
    <name>fs.default.name</name>
    <value>hdfs://master:9000</value>
  </property>
  <property>
    <name>hadoop.tmp.dir</name>
    <value>file:/usr/hadoop-2.7.4/tmp</value>
  </property>
</configuration>
5. Modify hdfs-site.xml
<configuration>
  <property>
    <name>dfs.datanode.data.dir</name>
    <value>/usr/hadoop-2.7.4/hdf/data</value>
    <final>true</final>
  </property>
  <property>
    <name>dfs.namenode.name.dir</name>
    <value>/usr/hadoop-2.7.4/hdf/name</value>
    <final>true</final>
  </property>
</configuration>
6. Copy mapred-site.xml.template and name it mapred-site.xml
cp mapred-site.xml.template mapred-site.xml
7. Modify mapred-site.xml
<configuration>
  <property>
    <name>mapreduce.framework.name</name>
    <value>yarn</value>
  </property>
  <property>
    <name>mapreduce.jobhistory.address</name>
    <value>master:10020</value>
  </property>
  <property>
    <name>mapreduce.jobhistory.webapp.address</name>
    <value>master:19888</value>
  </property>
</configuration>
8. Modify yarn-site.xml
<configuration>
  <property>
    <name>yarn.nodemanager.aux-services.mapreduce.shuffle.class</name>
    <value>org.apache.mapred.ShuffleHandler</value>
  </property>
  <property>
      <name>yarn.nodemanager.aux-services</name>
      <value>mapreduce_shuffle</value>
  </property>
  <property>
    <name>yarn.resourcemanager.address</name>
    <value>master:8032</value>
  </property>
  <property>
    <name>yarn.resourcemanager.scheduler.address</name>
    <value>master:8030</value>
  </property>
  <property>
    <name>yarn.resourcemanager.resource-tracker.address</name>
    <value>master:8031</value>
  </property>
  <property>
    <name>yarn.resourcemanager.admin.address</name>
    <value>master:8033</value>
  </property>
  <property>
    <name>yarn.resourcemanager.webapp.address</name>
    <value>master:8088</value>
  </property>
</configuration>
9. Copy Hadoop among hosts
scp -r /usr/ hadoop-2.7.4 slave1:/usr
scp -r /usr/ hadoop-2.7.4 slave2:/usr
scp -r /usr/ hadoop-2.7.4 slave3:/usr
10. Configure environment variables for Hadoop of each host
Open the configuration file:
vi /etc/profile
Edit the content:
export HADOOP_HOME=/usr/hadoop-2.7.4
export PATH=$HADOOP_HOME/bin:$HADOOP_HOME/sbin:$PATH
export HADOOP_LOG_DIR=/usr/hadoop-2.7.4/logs
export YARN_LOG_DIR=$HADOOP_LOG_DIR
Implement the configuration file:
source /etc/profile

Start Hadoop

1. Format namenode
cd /usr/hadoop-2.7.4/sbin
hdfs namenode -format
2. Start
cd /usr/hadoop-2.7.4/sbin
start-all.sh
3. Check processes
If processes on master contain ResourceManager, SecondaryNameNode and NameNode, Hadoop starts successfully. For example:
2212 ResourceManager
2484 Jps
1917 NameNode
2078 SecondaryNameNode
If processes on each slave contain DataNode and NodeManager, Hadoop starts successfully. For example:
17153 DataNode
17334 Jps
17241 NodeManager

Running wordcount

The wordcount built in Hadoop can be called directly. After Hadoop starts, use the following command to work with files in HDFS:
hadoop fs -mkdir input
hadoop fs -put input.txt /input
hadoop jar share/hadoop/mapreduce/hadoop-mapreduce-examples-2.7.4.jar wordcount /input /output/

The above result shows that Hadoop is installed successfully.

View output directory

hadoop fs -ls /output

View output result

hadoop fs -cat /output/part-r-00000

Note:
For more information on how to run Hadoop in stand-alone and pseudo-distributed modes, see Get Started with Hadoop on the official website.
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