Question - What are the three modes that Hadoop can run?
Answer -
Local Mode or Standalone Mode:
By default, Hadoop is configured to operate in a no distributed mode. It runs as a single Java process. Instead of HDFS, this mode utilizes the local file system. This mode is more helpful for debugging, and there isn't any requirement to configure core-site.xml, hdfs-site.xml, mapred-site.xml, masters & slaves. Standalone mode is ordinarily the quickest mode in Hadoop.
Pseudo-distributed Mode:
In this mode, each daemon runs on a separate java process. This mode requires custom configuration ( core-site.xml, hdfs-site.xml, mapred-site.xml). The HDFS is used for input and output. This mode of deployment is beneficial for testing and debugging purposes.
Fully Distributed Mode:
It is the production mode of Hadoop. One machine in the cluster is assigned as NameNode and another as Resource Manager exclusively. These are masters. Rest nodes act as Data Node and Node Manager. These are the slaves. Configuration parameters and environment need to be defined for Hadoop Daemons. This mode gives fully distributed computing capacity, security, fault endurance, and scalability.