As Hadoop is a distributed system with many components, and has a reputation of getting quite complex, it is important to understand the basic Architecture before we start with the deployments.
In this chapter, we will take a look at the Architecture and the recipes to deploy a Hadoop cluster in various modes. This chapter will also cover recipes on commissioning and decommissioning nodes in a cluster.
The recipes in this chapter will primarily focus on deploying a cluster based on an Apache Hadoop distribution, as it is the best way to learn and explore Hadoop.
Note
While the recipes in this chapter will give you an overview of a typical configuration, we encourage you to adapt this design according to your needs. The deployment directory structure varies according to IT policies within an organization. All our deployments will be based on the Linux operating system, as it is the most commonly used platform for Hadoop in production. You can use any flavor of Linux; the recipes are very generic in nature and should work on all Linux flavors, with the appropriate changes in path and installation methods, such as yum or apt-get.
Hadoop is a framework and not a tool. It is a combination of various components, such as a filesystem, processing engine, data ingestion tools, databases, workflow execution tools, and so on. Hadoop is based on client-server Architecture with a master node for each storage layer and processing layer.
Namenode is the master for Hadoop distributed file system (HDFS) storage and ResourceManager is the master for YARN (Yet Another Resource Negotiator). The Namenode stores the file metadata and the actual blocks/data reside on the slave nodes called Datanodes. All the jobs are submitted to the ResourceManager and it then assigns tasks to its slaves, called NodeManagers. In a highly available cluster, we can have more than one Namenode and ResourceManager.
Both masters are each a single point of failure, which makes them very critical components of the cluster and so care must be taken to make them highly available.
Although there are many concepts to learn, such as application masters, containers, schedulers, and so on, as this is a recipe book, we will keep the theory to a minimum.