Talend – Hadoop Distributed File System

Talend - Hadoop Distributed File System - myTechMint

Settings and Pre-requisites

Before we proceed into Talend with HDFS, we should learn about settings and pre-requisites that should be met for this purpose.
Here we are running Cloudera quickstart 5.10 VM on virtual box. A Host-Only Network must be used in this VM.
Host-Only Network IP: 192.168.56.101
Settings and Pre-requisites
You must have the same host running on cloudera manager also.
You must have the same host running on cloudera manager also.
Now on your windows system, go to c:WindowsSystem32Driversetchosts and edit this file using Notepad as shown below.
c:WindowsSystem32Driversetchosts and edit this file using Notepad
Similarly, on your cloudera quickstart VM, edit your /etc/hosts file as shown below.
sudo gedit /etc/hosts
cloudera quickstart VM, edit your /etc/hosts file

Setting Up Hadoop Connection

In the repository panel, go to Metadata. Right click Hadoop Cluster and create a new cluster. Give the name, purpose and description for this Hadoop cluster connection.
Click Next.
Setting Up Hadoop Connection
Select the distribution as cloudera and choose the version which you are using. Select the retrieve configuration option and click Next.
Select the retrieve configuration option and click Next.
Enter the manager credentials (URI with port, username, password) as shown below and click Connect. If the details are correct, you will get Cloudera QuickStart under discovered clusters.
If the details are correct, you will get Cloudera QuickStart under discovered clusters.
Click Fetch. This will fetch all the connections and configurations for HDFS, YARN, HBASE, HIVE.
Select All and click Finish.
the connections and configurations for HDFS, YARN, HBASE, HIVE.
Note that all the connection parameters will be auto-filled. Mention cloudera in the username and click Finish.
cloudera in the username and click Finish
With this, you have successfully connected to a Hadoop Cluster.
successfully connected to a Hadoop Cluster.

Connecting to HDFS

In this job, we will list all the directories and files which are present on HDFS.
Firstly, we will create a job and then add HDFS components to it. Right click on the Job Design and create a new job – hadoopjob.
Now add 2 components from the palette – tHDFSConnection and tHDFSList. Right click tHDFSConnection and connect these 2 components using ‘OnSubJobOk’ trigger.
Now, configure both the talend hdfs components.
Connecting to HDFS
In tHDFSConnection, choose Repository as the Property Type and select the Hadoop cloudera cluster which you created earlier. It will auto-fill all the necessary details required for this component.
select the Hadoop cloudera cluster
In tHDFSList, select “Use an existing connection” and in the component list choose the tHDFSConnection which you configured.
Give the home path of HDFS in HDFS Directory option and click the browse button on the right.
HDFS Directory option and click the browse button on the right
If you have established the connection properly with the above-mentioned configurations, you will see a window as shown below. It will list all the directories and files present on HDFS home.
the directories and files present on HDFS home
You can verify this by checking your HDFS on cloudera. 
You can verify this by checking your HDFS on cloudera

Reading file from HDFS

In this section, let us understand how to read a file from HDFS in Talend. You can create a new job for this purpose, however here we are using the existing one.
Drag and Drop 3 components – tHDFSConnection, tHDFSInput and tLogRow from the palette to designer window.
Right click tHDFSConnection and connect tHDFSInput component using ‘OnSubJobOk’ trigger.
Right click tHDFSInput and drag a main link to tLogRow.
Reading file from HDFS
Note that tHDFSConnection will have the similar configuration as earlier. In tHDFSInput, select “Use an existing connection” and from the component list, choose tHDFSConnection.
In the File Name, give the HDFS path of the file you want to read. Here we are reading a simple text file, so our File Type is Text File. Similarly, depending on your input, fill the row separator, field separator and header details as mentioned below. Finally, click the Edit schema button.
tHDFSConnection
Since our file is just having plain text, we are adding just one column of type String. Now, click Ok.
Note − When your input is having multiple columns of different types, you need to mention the schema here accordingly.
adding just one column of type String
In tLogRow component, click Sync columns in edit schema.
Select the mode in which you want your output to be printed.
tLogRow component
Finally, click Run to execute the job.
Once you were successful in reading a HDFS file, you can see the following output.
successful in reading a HDFS file

Writing File to HDFS

Let’s see how to write a file from HDFS in Talend. Drag and Drop 3 components – tHDFSConnection, tFileInputDelimited and tHDFSOutput from the palette to designer window.
Right click on tHDFSConnection and connect tFileInputDelimited component using ‘OnSubJobOk’ trigger.
Right click on tFileInputDelimited and drag a main link to tHDFSOutput.
Writing File to HDFS
Note that tHDFSConnection will have the similar configuration as earlier.
Now, in tFileInputDelimited, give the path of input file in File name/Stream option. Here we are using a csv file as an input, hence the field separator is “,”.
Select the header, footer, limit according to your input file. Note that here our header is 1 because the 1 row contains the column names and limit is 3 because we are writing only first 3 rows to HDFS.
Now, click edit schema.
tHDFSConnection
Now, as per our input file, define the schema. Our input file has 3 columns as mentioned below.
define the schema
In tHDFSOutput component, click sync columns. Then, select tHDFSConnection in Use an existing connection. Also, in File name, give a HDFS path where you want to write your file.
Note that file type will be text file, Action will be “create”, Row separator will be “n” and field separator is “;”
tHDFSOutput component
Finally, click Run to execute your job. Once the job has executed successfully, check if your file is there on HDFS.
file is there on HDFS
Run the following hdfs command with the output path you had mentioned in your job.
hdfs dfs -cat /input/talendwrite
You will see the following output if you are successful in writing on HDFS.
writing on HDFS
 

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