1. Oozie runs as a service in the cluster and clients submit workflow definitions for immediate or later processing. Oozie workflow consists of action NODES and control-flow nodes.
2. An action node represents a workflow task, e.g., moving files into HDFS, running a MAPREDUCE, Pig or Hive JOBS, importing data using Sqoop or running a shell script of a program written in Java.
3. A control-flow node controls the workflow execution between actions by allowing constructs like conditional logic wherein different branches may be followed depending on the result of EARLIER action node. Start Node, End Node and Error Node fall under this category of nodes.

• Start Node, designates start of the workflow job.
• End Node, SIGNALS end of the job.
• Error Node, designates an occurrence of error and corresponding error message to be printed.

At the end of execution of workflow, HTTP callback is used by Oozie to update client with the workflow status. Entry-to or exit-from an action node may also trigger callback.

At the end of execution of workflow, HTTP callback is used by Oozie to update client with the workflow status. Entry-to or exit-from an action node may also trigger callback.