How to scale a Debian Hadoop cluster

This article introduces how to expand the Debian Hadoop cluster, mainly covering two ways: dynamic capacity expansion (add nodes) and dynamic capacity reduction (removal nodes).

1. Dynamic expansion: Add new nodes

1. Configuration modification: Modify hdfs-site.xml on the NameNode node, add the dfs.hosts property, and list the network addresses of all DataNode nodes that are allowed to connect; modify yarn-site.xml on the ResourceManager node, and add the yarn.resourcemanager.nodes.include-path property, and list the network addresses of all NodeManager nodes that are allowed to connect.

2. New node preparation: Install Hadoop on the new node and configure environment variables. Modify the slaves file (or include file, depending on your configuration) of the new node and add the hostnames of all DataNode and NodeManager.

3. Start the service: Start the DataNode and NodeManager daemons on the new node:

 hadoop-daemon.sh start datanode
yarn-daemon.sh start nodemanager

4. Verify the capacity expansion: Use hdfs dfsadmin -refreshNodes and yarn rmadmin -refreshNodes commands to refresh the node list to verify that the new node has successfully joined the cluster.

2. Dynamic scaling: Remove nodes

1. Prepare to remove: Before removing the node, notify the NameNode so that HDFS can copy the data blocks to other DataNode nodes to ensure data security.

2. Stop service: Stop the DataNode and NodeManager daemons on the node to be removed:

 hadoop-daemon.sh stop datanode
yarn-daemon.sh stop nodemanager

3. Update configuration: Remove the host name of the node to be removed from the slaves file (or include file).

4. Verify the size reduction: Use hdfs dfsadmin -refreshNodes and yarn rmadmin -refreshNodes commands to refresh the node list and confirm that the node has been removed successfully.

Important tip: Before performing dynamic scaling operations, be sure to back up configuration files and data. Ensure that the operating system version, Hadoop version and network configuration of all nodes are consistent to ensure the stability and data integrity of the cluster. Any operation should be carried out with caution and the cluster status should be closely monitored.

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