For a backup, the destination is the backup cluster, and the source is the production cluster.

The cluster establishing the peer relationship gains access to the source cluster and can run the export command, list HDFS files, and read files for copying them to the destination cluster. These are all the actions performed by the replication process whenever the defined schedule goes into action.

Defining the replication starts from the Cloudera Manager Admin Console on the backup cluster.

1. Log in to Cloudera Manager Admin Console on the backup cluster.
2. Click the Backup tab and select Peers from the menu.
3. On the Peers page, click Add Peer:
   
   
   
   
4. On the Add Peer page:
   1. Peer Name - Enter a meaningful name for the cluster that you want to back up. This peer name becomes available in the next step, to be selected as the source for the replication.
   2. Peer URL - Enter the URL for the Cloudera Manager Admin Console running on the master node of the cluster.
   3. Peer Admin Username - Enter the administrator user account for the production cluster.
   4. Peer Admin Password - Enter the password for the administrator account for the production cluster.
      
      
      
      
5. Click Add Peer to save your settings, connect to the production cluster, and establish this peer relationship.

After the system establishes and verifies the connection to the peer, the Peers page re-displays, showing the Status column as Connected (note the green check-mark):

With the peer relationship established from destination to source, create a schedule to replicate HDFS files from the source (production cluster) to the destination (backup cluster).

From the Cloudera Manager Admin Console on the backup cluster:

1. Click the Backup tab and select Replication Schedules from the menu.
2. On the Replication Schedules page, select Create Schedule > HDFS Replication.
3. On the Create HDFS Replication page, click the General tab to display the default schedule options:
   1. Source - Make sure the cluster node selected in the drop-down is the production cluster (the cluster to be backed up).
   2. Source Path - Specify the directory name on the production cluster holding the files to back up. Use an asterisk (*) on the directory name to specify that only the explicit directory and no others should be created on the destination. Without the asterisk, directories may be nested inside a containing directory on the destination.
   3. Destination - Select the cluster to use as the target of the replication process, typically, the cluster to which you have logged in and the cluster to which you want to backup HDFS data.
   4. Destination Path - Specify a directory name on the backup cluster.
   5. Schedule - Immediate.
   6. Run As Username - Leave as Default.
   7. Scheduler Pool - Leave as Default.
4. Click Save Schedule.

The files are replicated from the source cluster to the backup cluster immediately.

When the process completes, the Replication Schedules page re-displays, showing a green check-mark and time-stamp in the Last Run column.

Verify that the HDFS files are now on the backup cluster by using the HDFS File Browser or the hadoop fs -ls command (shown below):

The HDFS files are now on both the production cluster and the backup cluster.

You can now use the backup as a source for a restore onto the production system when needed.

To restore HDFS files on the production cluster, establish a Peer relationship from the destination to the source for the restore.

Log in to the Cloudera Manager Admin Console on the production cluster.

1. Click the Backup tab and select Peers from the menu.
2. On the Peers page, click Add Peers.

   
   

   
   
   

3. On the Add Peer page:
   1. Peer Name - Enter a meaningful name for the cluster that you want to restore data from, for example, BackupCluster.
   2. Peer URL - Enter the URL for the Cloudera Manager Admin Console running on the master node of the cluster.
   3. Peer Admin Username - Enter the administrator user name for the peer cluster.
   4. Peer Admin Password - Enter the password for the administrator user account.

      
      

      
      
      

4. Click Add Peer to save the settings, connect to the backup cluster, and establish the peer relationship.

Once the system connects and tests the peer relationship, the Peers page lists its name, URL, and Status (Connected):

The backup cluster is now available as a peer, for use in a Replication Schedule.

The goal in these steps is to create a replication schedule that can be used when needed, in the future, but to leave it in a disabled state. However, because Replication Schedules cannot be created in a disabled state, you initially set the date far into the future and then disable the schedule in a subsequent step.

From the Cloudera Manager Admin Console on the production cluster:

1. Click the Backup tab and select Replication Schedules from the menu.
2. On the Replication Schedules page, select Create Schedule > HDFS Replication.
3. On the General settings tab of the Create HDFS Replication page:
   1. Source - Make sure the cluster node selected in the drop-down is the backup cluster.
   2. Source Path - Specify the directory name that you want to back up. Use an asterisk (*) on the directory name to specify that only the explicit directory and no others should be created on the destination.
   3. Destination - Select the cluster to use as the target for the replication process.
   4. Destination Path - Specify a directory name on the backup cluster.
        Important: The path is a new directory on the example production cluster.
   5. Schedule - Set to a time far in the future, so that the schedule does not run as soon as it is saved.
   6. Run As Username - Leave as Default.
   7. Scheduler Pool - Leave as Default.

   
   

   
   
   

4. Click Save Schedule.

The Replication Schedule is saved and displays in the Replication Schedules list, with the future date listed in the Next Run column.

Before continuing, immediately disable this newly created Replication Schedule.

1. On the Replication Schedules page, select the replication schedule.
2. From the Actions drop-down menu, select Disable. When the page refreshes, Disabled displays in the Next Run column:

You can leave restore Replication Schedules pre-configured and disabled in this way so they are ready to use in the event of a catastrophic data loss. Before relying on this approach, test the schedule.

The Replication Schedule defined in the example restores data to a specific directory path identified for the purpose of restoration (/user/cloudera-restored) rather than targeting the original source directory path.

From the Cloudera Manager Admin Console on the production cluster, with Replication Schedules page displayed:

1. On the Replication Schedules page, select the disabled replication schedule.
2. Select Actions > Run Now.
   
   
   
   

When the replication process completes, disable the Replication Schedule once again:

1. On the Replication Schedules page, select the replication schedule.
2. Select Actions > Disable .

You can now verify that the files have been replicated to the destination directory path.

To manually verify that your data has been restored to the source cluster, you can use the HDFS File Browser or the hadoop command-line, as shown here:

Compare the restored data in /user/cloudera-restored to the data in /user/cloudera to validate that the restore schedule operates as expected.

At this point, until you need to actually restore production HDFS data files, you can leave the Replication Schedule disabled.

  Important: In a production environment, only one Replication Schedule for a given dataset should be active at the same time. In this example, the Replication Schedule that created the backup has not been disabled yet, because the HDFS files from the backup cluster were restored to a different path on the example production cluster.

Disabling any existing replication schedule for HDFS backups can help prevent the replication of lost or corrupted data files over existing backups.

At the Cloudera Manager Admin Console on the backup cluster:

1. Select Backup > Replication Schedules.
2. On the Replication Schedules page, select the schedule.
3. From the Actions drop-down menu, select Disable:

When the Replication Schedules pages refreshes, you see Disabled in the Next Run column for the schedule.

With the replication schedule disabled, you can edit the replication schedule verified previously (Step 4: Test the Restore Replication Schedule) and restore the data to the production cluster.

From the Cloudera Manager Admin Console on the production cluster:

1. Click the Backup tab and select Replication Schedules from the menu.
2. On the Replication Schedules page, select Create Schedule > HDFS Replication.
3. On the General settings tab of the Create HDFS Replication page:
   1. Source - Name of the backup cluster from which to pull the data. For this example, the source is the backup cluster.
   2. Source Path - The path on the backup cluster that contains the data you want to restore. Use the asterisk (*) at the end of the directory name to prevent extraneous sub-directories being created on the destination.
   3. Destination - The name of the cluster on which to restore the data, in which case, the example production cluster.
   4. Destination Path - Directory in which to restore the HDFS data files, in this case, the directory on the example production system.
   5. Schedule - Once.
   6. Start Time - Leave set to the future date and time that you originally defined in Step 2: Configure Replication Schedule to Test the Restore.
   7. Run as Username - Leave set as Default.
   
   
   
   
   
4. Click Save Schedule.

The settings for the Replication Schedule are saved, and the page refreshes. Because this replication schedule is currently disabled, you must actively run the schedule to restore the data.

While still on the Replication Schedules page:

1. Select the edited replication schedule.
2. From the Actions drop-down menu, select Run Now.

The replication schedule executes and restores the HDFS files to the original location.

When the process completes, the Replication Schedules page displays the time-stamp and check-mark in the Last Run column for the schedule.

You can now disable the schedule, and after verifying that HDFS data has been successfully restored to the production cluster, you can re-enable the backup schedule. While still displaying the Replication Schedules page on the production cluster:

1. Select the replication schedule used for the restore.
2. Edit its configuration again, to point to a non-production directory.
3. Select Actions > Disable.

After confirming that the schedule has been disabled—you see Disabled in the Next Run column for this schedule—but before re-enabling the backup schedule, verify that the HDFS files have been restored to the production cluster.

With data restored to the production cluster and the replication schedule on the production cluster disabled, you can re-enable the replication schedule on the backup cluster.

1. At the backup cluster, log in to the Cloudera Manager Admin Console.
2. Select Backup > Replication Schedules.
3. On the Replication Schedules page, select the appropriate replication schedule to back up the production cluster.
4. From the Actions drop-down menu, select Enable.

This concludes the tutorial. In an actual production environment, you should configure replication schedules to regularly backup production systems. For restoring files from any backup, you can create and test a replication schedules in advance, as shown in this tutorial.

Alternatively, you can create a replication schedule to restore data specifically when needed. See How To Back Up and Restore Apache Hive Data Using Cloudera Enterprise BDR for details.

See Backup and Disaster Recovery and BDR Tutorials for more information about Cloudera Enterprise BDR.