HDFS to HDFS line copy application

Summary

Ingest and backup hadoop HDFS data as lines from one cluster to another in a fault tolerant way. This application reads lines from the configured source path and writes them to the destination file path. The source code is available at: https://github.com/DataTorrent/app-templates/tree/master/hdfs-line-copy.

Please send feedback or feature requests to: feedback@datatorrent.com

This document has a step-by-step guide to configure, customize, and launch this application.

Steps to launch application

1. Click on the AppHub tab from the top navigation bar.

2. Page listing the applications available on AppHub is displayed. Search for HDFS to see all applications related to HDFS.

Click on import button for HDFS to HDFS Line Copy App

1. Notification is displayed on the top right corner after application package is successfully imported.

2. Click on the link in the notification which navigates to the page for this application package.

   Detailed information about the application package like version, last modified time, and short description is available on this page. Click on launch button for HDFS line copy application.

3. Launch HDFS-line-copy dialogue is displayed. One can configure name of this instance of the application after from this dialogue.

4. Select Use saved configuration option. This displays list of pre-saved configurations. Please select sandbox-memory-conf.xml or cluster-memory-conf.xml depending on whether your environment is the DataTorrent sandbox, or other cluster.

5. Select Specify custom properties option. Click on add default properties button.

6. This expands a key-value editor pre-populated with mandatory properties for this application. Change values as needed.

   For example, suppose we wish to process lines from all the files in /user/appuser/input from source-cluster and send the output to output.txt in /user/appuser/output in the destination-cluster. Properties should be set as follows:

   name	value
   dt.operator.fileOutput.prop.filePath	hdfs://destination-cluster/user/appuser/output
   dt.operator.fileOutput.prop.outputFileName	output.txt
   dt.operator.recordReader.prop.files	hdfs://source-cluster/user/appuser/input

   Details about configuration options are available in Configuration options section.

7. Click on Launch button on bottom right corner to launch the application. Notification is displayed on the top right corner after application is launched successfully and includes the Application ID which can be used to monitor this instance and find its logs.

8. Click on the Monitor tab from the top navigation bar.

9. Page with listing of all running applications is displayed. Search for current application based on name or application id or any other relevant field. Click on the application name or id to navigate to application instance details page.

10. Application instance details page shows key metrics for monitoring the application status. The logical tab shows application DAG, Stram events, operator status based on logical operators, stream status, and a chart with key metrics.

11. Click on the physical tab to look at the status of physical instances of the operator, containers etc.

Configuration options

Mandatory properties

End user must specify the values for these properties (all properties are strings).

Property	Description	Example
dt.operator.recordReader.prop.files	HDFS path for input file or directory	/user/appuser/input/directory1 /user/appuser/input/file2.log hdfs://node1.corp1.com/user/user1/input
dt.operator.fileOutput.prop.outputFileName	Name of the output file. This name will be appended with suffix for each part.	output.txt
dt.operator.fileOutput.prop.filePath	HDFS path for the output directory. Generally, this refers to path on the hadoop cluster on which app is running.	/user/appuser/output

Advanced properties

There are pre-saved configurations based on the application environment. Recommended settings for datatorrent sandbox edition are in sandbox-memory-conf.xml and for a cluster environment in cluster-memory-conf.xml.

Property	Description	Type	Default for cluster -memory -conf.xml	Default for sandbox -memory -conf.xml
dt.operator.recordReader.prop.minReaders	Minimum number of BlockReader partitions for parallel reading.	int	1	1
dt.operator.recordReader.prop.maxReaders	Maximum number of BlockReader partitions for parallel reading.	int	16	1

You can override default values for advanced properties by specifying custom values for these properties in the step specify custom property step mentioned in steps to launch an application.

Steps to customize the application

1. Make sure you have following utilities installed on your machine and available on PATH in environment variables

   • Java : 1.7.x
   • maven : 3.0 +
   • git : 1.7 +
   • Hadoop (Apache-2.2)+

2. Use following command to clone the examples repository:

   git clone git@github.com:DataTorrent/app-templates.git

3. Change directory to examples/tutorials/hdfs-to-kafka-sync:

   cd examples/tutorials/hdfs-line-copy

4. Import this maven project in your favorite IDE (e.g. eclipse).

5. Change the source code as per your requirements. Some tips are given as commented blocks in the Application.java for this project.

6. Make respective changes in the test case and properties.xml based on your environment.

7. Compile this project using maven:

   mvn clean package

   This will generate the application package with the .apa extension inside the target directory.

8. Go to DataTorrent UI Management console on web browser. Click on the Develop tab from the top navigation bar.

9. Click on upload package button and upload the generated .apa file.

10. Application package page is shown with the listing of all packages. Click on the Launch button for the uploaded application package. Follow the steps for launching an application.