A Hadoop developer primarily designs, develops, installs, and configures Hadoop systems. They write complex MapReduce programs to process large amounts of data, and manage Hadoop jobs using scheduler. They also ensure data processing is secure, efficient, and fault-tolerant, while preserving data privacy. Their job involves data loading from disparate data sets, preprocessing using Hive and Pig. They also determine the optimal way to store the data in the HDFS (Hadoop Distributed File System). They work closely with the data team and system administrators to ensure optimal performance of the Hadoop ecosystem. They also troubleshoot problems and propose solutions as needed.