Question - What are Hadoop's primary operational modes?
Answer -
Hadoop supports three primary operational nodes.
- Standalone. Also referred to as Local mode, the Standalone mode is the default mode. It runs as a single Java process on a single node. It also uses the local file system and requires no configuration changes. The Standalone mode is used primarily for debugging purposes.
- Pseudo-distributed. Also referred to as a single-node cluster, the Pseudo-distributed mode runs on a single machine, but each Hadoop daemon runs in a separate Java process. This mode also uses HDFS, rather than the local file system, and it requires configuration changes. This mode is often used for debugging and testing purposes.
- Fully distributed. This is the full production mode, with all daemons running on separate nodes in a primary/secondary configuration. Data is distributed across the cluster, which can range from a few nodes to thousands of nodes. This mode requires configuration changes but offers the scalability, reliability and fault tolerance expected of a production system.