What are the steps to build high availability in Hadoop?

The steps to set up a high availability Hadoop cluster are as follows:

1. Prepare the environment:
2. Install JDK and set the JAVA_HOME environment variable.
3. Install and configure SSH service to ensure that nodes in the cluster can SSH login to each other.
4. Download Hadoop.
5. Download the stable version of Hadoop from the Apache official website and unzip it to a specified directory.
6. Setting up a Hadoop cluster:
7. Edit the hadoop-env.sh file at each node, configure the JAVA_HOME and relevant environment variables for Hadoop.
8. Edit the core-site.xml file at each node to configure general properties of Hadoop, such as file system type and default file system.
9. Edit the hdfs-site.xml file on each node to configure properties of HDFS, such as the replication factor, and the storage paths for the namenode and datanode.
10. Edit the yarn-site.xml file at each node to configure properties of YARN, such as the address of the ResourceManager and resource allocation for NodeManagers.
11. Edit the mapred-site.xml file on each node to configure properties for MapReduce, such as the address of the JobHistory Server and task schedulers.
12. Setting up Hadoop for high availability.
13. Edit the hdfs-site.xml file on the master node to configure the HA properties of HDFS, such as enabling HA, specifying the HTTP address and RPC address of the namenode.
14. Edit the hdfs-site.xml file on the master node to configure the address and storage path of the JournalNode.
15. Edit the hdfs-site.xml file on the master node to configure the address and port of ZooKeeper.
16. Edit the yarn-site.xml file on the master node to configure ResourceManager’s HA properties, such as enabling HA, specifying the HTTP address and RPC address of the RM.
17. Edit the yarn-site.xml file on the master node to configure the address and port of ZooKeeper.
18. Start the Hadoop cluster.
19. Format HDFS: Execute the command hdfs namenode -format on the master node.
20. Start HDFS by executing the command start-dfs.sh on the master node.
21. Start YARN: Run the command start-yarn.sh on the master node.
22. Start other components such as the JobHistory Server.
23. Validate Hadoop’s high availability.
24. Access HDFS: Ensure the file system is functioning properly by accessing HDFS through a browser or command line.
25. Submit a MapReduce task: Submit a simple MapReduce task and ensure that the job runs correctly.
26. Monitor cluster status: Check the status and running condition of the cluster via Hadoop Web UI or command line tools.

The above are the basic steps for setting up a high availability Hadoop cluster, the specifics and configurations may vary depending on different versions and requirements.