Any command to get active namenode for nameservice in hadoop?

Question

The command:

hdfs haadmin -getServiceState machine-98

Works only if you know the machine name. Is there any command like:

hdfs haadmin -getServiceState <nameservice>

which can tell you the IP/hostname of the active namenode?

Answer 1

In a High Availability Hadoop cluster, there will be 2 namenodes - one active and one standby.

To find the active namenode, we can try executing the test hdfs command on each of the namenodes and find the active name node corresponding to the successful run.

Below command executes successfully if the name node is active and fails if it is a standby node.

hadoop fs -test -e hdfs://<Name node>/

Unix script

active_node=''
if hadoop fs -test -e hdfs://<NameNode-1>/ ; then
active_node='<NameNode-1>'
elif hadoop fs -test -e hdfs://<NameNode-2>/ ; then
active_node='<NameNode-2>'
fi

echo "Active Dev Name node : $active_node"

Answer 2

To print out the namenodes use this command:

hdfs getconf -namenodes

To print out the secondary namenodes:

hdfs getconf -secondaryNameNodes

To print out the backup namenodes:

hdfs getconf -backupNodes

Note: These commands were tested using Hadoop 2.4.0.

Update 10-31-2014:

Here is a python script that will read the NameNodes involved in Hadoop HA from the config file and determine which of them is active by using the hdfs haadmin command. This script is not fully tested as I do not have HA configured. Only tested the parsing using a sample file based on the Hadoop HA Documentation. Feel free to use and modify as needed.

#!/usr/bin/env python
# coding: UTF-8
import xml.etree.ElementTree as ET
import subprocess as SP
if __name__ == "__main__":
    hdfsSiteConfigFile = "/etc/hadoop/conf/hdfs-site.xml"

    tree = ET.parse(hdfsSiteConfigFile)
    root = tree.getroot()
    hasHadoopHAElement = False
    activeNameNode = None
    for property in root:
        if "dfs.ha.namenodes" in property.find("name").text:
            hasHadoopHAElement = True
            nameserviceId = property.find("name").text[len("dfs.ha.namenodes")+1:]
            nameNodes = property.find("value").text.split(",")
            for node in nameNodes:
                #get the namenode machine address then check if it is active node
                for n in root:
                    prefix = "dfs.namenode.rpc-address." + nameserviceId + "."
                    elementText = n.find("name").text
                    if prefix in elementText:
                        nodeAddress = n.find("value").text.split(":")[0]                

                        args = ["hdfs haadmin -getServiceState " + node]  
                        p = SP.Popen(args, shell=True, stdout=SP.PIPE, stderr=SP.PIPE)

                        for line in p.stdout.readlines():
                            if "active" in line.lower():
                                print "Active NameNode: " + node
                                break;
                        for err in p.stderr.readlines():
                            print "Error executing Hadoop HA command: ",err
            break            
    if not hasHadoopHAElement:
        print "Hadoop High-Availability configuration not found!"