Chapter 5. Configuring Rack Awareness On HDP

Create a topology script and data file. The topology script must be executable.

Sample Topology Script Named rack-topology.sh

#!/bin/bash

# Adjust/Add the property "net.topology.script.file.name"
# to core-site.xml with the "absolute" path the this
# file. ENSURE the file is "executable".

# Supply appropriate rack prefix
RACK_PREFIX=default

# To test, supply a hostname as script input:
if [ $# -gt 0 ]; then

CTL_FILE=${CTL_FILE:-"rack_topology.data"}

HADOOP_CONF=${HADOOP_CONF:-"/etc/hadoop/conf"} 

if [ ! -f ${HADOOP_CONF}/${CTL_FILE} ]; then
 echo -n "/$RACK_PREFIX/rack "
 exit 0
fi

while [ $# -gt 0 ] ; do
 nodeArg=$1
 exec< ${HADOOP_CONF}/${CTL_FILE}
 result=""
 while read line ; do
 ar=( $line )
 if [ "${ar[0]}" = "$nodeArg" ] ; then
 result="${ar[1]}"
 fi
 done
 shift
 if [ -z "$result" ] ; then
 echo -n "/$RACK_PREFIX/rack "
 else
 echo -n "/$RACK_PREFIX/rack_$result "
 fi
done

else
 echo -n "/$RACK_PREFIX/rack "
fi

Sample Topology Data File Named rack_topology.data

# This file should be:
# - Placed in the /etc/hadoop/conf directory
# - On the Namenode (and backups IE: HA, Failover, etc)
# - On the Job Tracker OR Resource Manager (and any Failover JT's/RM's) 
# This file should be placed in the /etc/hadoop/conf directory.

# Add Hostnames to this file. Format <host ip> <rack_location>
192.168.2.10 01
192.168.2.11 02
192.168.2.12 03

Copy both of these files to the /etc/hadoop/conf directory on all cluster nodes.

Run the rack-topology.sh script to ensure that it returns the correct rack information for each host.

Stop HDFS using the applicable commands in the Controlling HDP Services Manually section of the HDP Reference Guide.

Add the following property to core-site.xml:

<property>
  <name>net.topology.script.file.name</name> 
  <value>/etc/hadoop/conf/rack-topology.sh</value>
</property>

Look in the NameNode logs located in /var/log/hadoop/hdfs/. For example: hadoop-hdfs-namenode-sandbox.log. You should see an entry like this:

014-01-13 15:58:08,495 INFO org.apache.hadoop.net.NetworkTopology: Adding a new node: /rack01/<ipaddress>

The Hadoop fsck command should return something like the following (if there are two racks):

Status: HEALTHY  
 Total size: 123456789 B 
 Total dirs: 0  
 Total files: 1  
 Total blocks (validated): 1 (avg. block size 123456789 B)
 Minimally replicated blocks: 1 (100.0 %)  
 Over-replicated blocks: 0 (0.0 %)  
 Under-replicated blocks: 0 (0.0 %)  
 Mis-replicated blocks: 0 (0.0 %)
 Default replication factor: 3  
 Average block replication: 3.0  
 Corrupt blocks: 0  
 Missing replicas: 0 (0.0 %)  
 Number of data-nodes: 40  
 Number of racks: 2  
FSCK ended at Mon Jan 13 17:10:51 UTC 2014 in 1 milliseconds

The Hadoop dfsadmin -report command will return a report that includes the rack name next to each machine. The report should look something like the following excerpted example:

[bsmith@hadoop01 ~]$ sudo -u hdfs hadoop dfsadmin -report
Configured Capacity: 19010409390080 (17.29 TB) 
Present Capacity: 18228294160384 (16.58 TB) 
DFS Remaining: 5514620928000 (5.02 TB) 
DFS Used: 12713673232384 (11.56 TB) 
DFS Used%: 69.75% 
Under replicated blocks: 181 
Blocks with corrupt replicas: 0  
Missing blocks: 0

-------------------------------------------------  
Datanodes available: 5 (5 total, 0 dead) 
 
Name: 192.168.90.231:50010 (h2d1.hdp.local) 
Hostname: h2d1.hdp.local 
Rack: /default/rack_02 
Decommission Status : Normal 
Configured Capacity: 15696052224 (14.62 GB) 
DFS Used: 314380288 (299.82 MB) 
Non DFS Used: 3238612992 (3.02 GB) 
DFS Remaining: 12143058944 (11.31 GB) 
DFS Used%: 2.00% 
DFS Remaining%: 77.36%
Configured Cache Capacity: 0 (0 B) 
Cache Used: 0 (0 B) 
Cache Remaining: 0 (0 B) 
Cache Used%: 100.00% 
Cache Remaining%: 0.00% 
Last contact: Thu Jun 12 11:39:51 EDT 2014