HDFS Sync App

Summary

Ingest and backup hadoop HDFS data from one cluster to another in a fault tolerant way for use cases such as disaster recovery. This application copies files from the configured source path to the destination file path. The source code is available at: https://github.com/DataTorrent/app-templates/tree/master/hdfs-sync.

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. AppHub link from top navigation bar

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

AppHub search for HDFS

Click on import button for HDFS Sync App.

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

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

  3. Launch HDFS-Sync-App dialogue is displayed. One can configure name of this instance of the application from this dialogue. Launch 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. Select saved configuration

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

  6. This expands a key-value editor pre-populated with mandatory properties for this application. Change values as needed. Properties editor For example, suppose we wish to copy all files in /user/appuser/input from remote-cluster to /user/appuser/archive on the host cluster (on which app is running). Properties should be set as follows:

    name value
    dt.operator.HDFSFileCopyModule.prop.outputDirectoryPath /user/appuser/archive
    dt.operator.HDFSInputModule.prop.files hdfs://remote-cluster/user/appuser/input

    This application is tuned for better performance if reading data from remote cluster to host cluster. 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. Application launch notification

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

  9. A page listing 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. Apps monitor listing

  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. Logical tab

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

Configuration options

Mandatory properties

End user must specify the values for these properties (these properties are all strings and are HDFS paths: the first is the destination and the second the source).

Property Example
dt.operator.HDFSFileCopyModule.prop.outputDirectoryPath
  • /user/appuser/output/dir1
  • hdfs://node1.corp1.com/user/appuser/output
dt.operator.HDFSInputModule.prop.files
  • /user/appuser/input/dir1
  • /user/appuser/input/dir2/file1.log
  • hdfs://node1.corp1.com/user/appuser/input

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.HDFSInputModule.prop.maxReaders Maximum number of BlockReader partitions for parallel reading. int 16 1
dt.operator.HDFSInputModule.prop.blocksThreshold Rate at which block metadata is emitted per second 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

  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-sync:

    cd examples/tutorials/hdfs-sync

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

  5. Change the source code as per your requirements. This application is for copying files from source to destination. Thus, Application.java does not involve any processing operator in between.

  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 .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. Develop tab

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

  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.