Diagnosing Zero Active YARN Nodes
When a Hadoop cluster encounters the issue of having zero active YARN nodes, it can severely impact the cluster's ability to execute and manage applications. Diagnosing the root cause of this problem is crucial for restoring the cluster's functionality.
Checking YARN Node Status
The first step in diagnosing the issue is to check the status of the YARN nodes in the cluster. You can use the following command to view the list of YARN nodes and their status:
yarn node -list
This command will display the following information for each YARN node:
Node ID |
Node State |
Rack |
Used |
Available |
Containers |
Node Health |
... |
... |
... |
... |
... |
... |
... |
If the output shows that all YARN nodes have a "DECOMMISSIONED" or "LOST" state, it indicates that there are no active YARN nodes in the cluster.
Analyzing YARN Logs
To further investigate the issue, you can examine the YARN logs for any error messages or clues that might help identify the root cause. The YARN logs are typically located in the /var/log/hadoop-yarn
directory on the ResourceManager and NodeManager nodes.
You can use the following command to view the YARN ResourceManager log:
cat /var/log/hadoop-yarn/yarn-resourcemanager-*.log
Similarly, you can view the YARN NodeManager logs by running:
cat /var/log/hadoop-yarn/yarn-nodemanager-*.log
Carefully review the logs for any error messages, warnings, or unusual behavior that might provide insights into the cause of the zero active YARN nodes issue.
Checking Hadoop Configuration
Another step in the diagnosis process is to review the Hadoop configuration files, such as yarn-site.xml
, hdfs-site.xml
, and core-site.xml
, to ensure that the cluster is properly configured. Look for any misconfigured or missing parameters that might be causing the YARN nodes to become inactive.
By following these steps, you can effectively diagnose the root cause of the zero active YARN nodes issue and take the necessary actions to resolve the problem.