['Apache Nifi Architecture']

Apache NiFi has a processor, flow controller, and web server that execute on the JVM machine. Additionally, it also includes three repositories, as shown in the figure, which are the flow-file repository, the content repository, and the provenance repository. NiFi runs within a JVM (Java Virtual Machine) on a host operating system, and every piece of data or metadata is stored in repositories. The well-organized architecture of NiFi is as follows:

Flowfile Repository

This repository stores the current state and attributes of every flowfile that goes through the data flows of Apache NiFi. The default location of this repository is in the root directory of Apache NiFi. The location of this repository can be changed by changing the property named "nifi.flowfile.repository.directory".

Content Repository

This repository contains all the content present in all the flowfiles of NiFi. Its default directory is also in the root directory of NiFi, and it can be changed using the "org.apache.nifi.controller.repository.FileSystemRepository" property. This directory uses a lot of disk space, so it is advisable to have enough space on the installation disk.

Provenance repository

The provenance repository is the repository that stores all the provenance event data. Event data is indexed and searchable within each location. It allows the user to check information about FlowFile, which means it tracks and stores all the events of all flow files that flow in the Apache NiFi. It also enables the troubleshooting if any issue occurs while processing FlowFile

The provenance repository has been divided into two types:

Volatile provenance repository - All provenance data is lost after restart in this repository.
Persistence Provenance Repository: The default directory of persistence provenance is in the root directory of Apache NiFi. It can be changed using the "apache.nifi.provenance.PersistanceProvenanceRepository" property.