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
-
Click on the AppHub tab from the top navigation bar.
-
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
-
Notification is displayed on the top right corner after application package is successfully imported.
-
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. -
Launch HDFS-line-copy
dialogue is displayed. One can configure name of this instance of the application after from this dialogue. -
Select
Use saved configuration
option. This displays list of pre-saved configurations. Please selectsandbox-memory-conf.xml
orcluster-memory-conf.xml
depending on whether your environment is the DataTorrent sandbox, or other cluster. -
Select
Specify custom properties
option. Click onadd default properties
button. -
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
fromsource-cluster
and send the output tooutput.txt
in/user/appuser/output
in thedestination-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.
-
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. -
Click on the
Monitor
tab from the top navigation bar. -
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.
-
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. -
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 |
|
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
-
Make sure you have following utilities installed on your machine and available on
PATH
in environment variables -
Use following command to clone the examples repository:
git clone git@github.com:DataTorrent/app-templates.git
-
Change directory to
examples/tutorials/hdfs-to-kafka-sync
:cd examples/tutorials/hdfs-line-copy
-
Import this maven project in your favorite IDE (e.g. eclipse).
-
Change the source code as per your requirements. Some tips are given as commented blocks in the
Application.java
for this project. -
Make respective changes in the test case and
properties.xml
based on your environment. -
Compile this project using maven:
mvn clean package
This will generate the application package with the
.apa
extension inside thetarget
directory. -
Go to DataTorrent UI Management console on web browser. Click on the
Develop
tab from the top navigation bar. -
Click on
upload package
button and upload the generated.apa
file. -
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.