Adding upstream version 1.44.3.upstream/1.44.3upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

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+### Understand the Alert
+
+The Netdata Agent monitors the number of DataNodes that are currently dead. Receiving this alert indicates that there are dead DataNodes in your HDFS cluster. The NameNode characterizes a DataNode as dead if no heartbeat message is exchanged for approximately 10 minutes. Any data that was registered to a dead DataNode is not available to HDFS anymore.
+
+This alert is triggered into critical when the number of dead DataNodes is 1 or more.
+
+### Troubleshoot the Alert 
+
+1. Fix corrupted or missing blocks.
+
+    ```
+    root@netdata #  hadoop dfsadmin -report
+    ```
+
+    Inspect the output and check which DataNode is dead.
+
+2. Connect to the DataNode and check the log of the DataNode. You can also check for errors in the system services.
+
+    ```
+    root@netdata #  systemctl status hadoop
+    ```
+
+   Restart the service if needed.
+
+
+3. Verify that the network connectivity between NameNode and DataNodes is functional. You can use tools like `ping` and `traceroute` to confirm the connectivity.
+
+4. Check the logs of the dead DataNode(s) for any issues. Log location may vary depending on your installation, but you can typically find them in the `/var/log/hadoop-hdfs/` directory. Analyze the logs to identify any errors or issues that may have caused the DataNode to become dead.
+
+    ```
+    root@netdata # tail -f /var/log/hadoop-hdfs/hadoop-hdfs-datanode-*.log
+    ```
+
+5. If the DataNode service is not running or has crashed, attempt to restart it.
+
+    ```
+    root@netdata # systemctl restart hadoop
+    ```
+
+### Useful resources
+
+1. [Hadoop Commands Guide](https://hadoop.apache.org/docs/current/hadoop-project-dist/hadoop-common/CommandsManual.html)
+
+Remember that troubleshooting and resolving issues, especially on a production environment, requires a good understanding of the system and its architecture. Proceed with caution and always ensure data backup and environmental safety before performing any action.