Top 15 Apache Nifi Interview Questions You Must Prepare 07.Jul.2022

You can certainly add attributes to your FlowFiles at anytime, that’s the whole point of separating metadata from the actual data. Essentially, one FlowFile represents an object or a message moving through NiFi. Each FlowFile contains a piece of content, which is the actual bytes. You can then extract attributes from the content, and store them in memory. You can then operate against those attributes in memory, without touching your content. By doing so you can save a lot of IO overhead, making the whole flow management process extremely efficient.

You can use to load custom key, value pair you can use custom properties registry, which can be configure as (in nifi.properties file)

nifi.variable.registry.properties=/conf/nifi_registry

And you can put key value pairs in that file and you can use that properties in you NiFi processor using expression language e.g. ${OS} , if you have configured that property in registry file.

Template is a re-usable workflow. Which you can import and export in the same or different NiFi instances. It can save lot of time rather than creating Flow again and again each time. Template is created as an xml file.

No, from NiFi 1.0 there is 0-master philosophy is considered. And each node in the NiFi cluster is the same. NiFi cluster is managed by the Zookeeper. Apache ZooKeeper elects a single node as the Cluster Coordinator, and failover is handled automatically by ZooKeeper. All cluster nodes report heartbeat and status information to the Cluster Coordinator. The Cluster Coordinator is responsible for disconnecting and connecting nodes. Additionally, every cluster has one Primary Node, also elected by ZooKeeper.

As we mentioned previously, contents are not stored in the FlowFile. They are stored in the content repository and referenced by the FlowFile. This allows the contents of FlowFiles to be stored independently and efficiently based on the underlying storage mechanism.

NiFi is helpful in creating DataFlow. It me you can trfer data from one system to another system as well as process the data in between.

Huge volume of data can trit from DataFlow. As data moves through NiFi, a pointer to the data is being passed around, referred to as a FlowFile. The content of the FlowFile is only accessed as needed.

Processor is a main component in the NiFi, which will really work on the FlowFile content and helps in creating, sending, receiving, trforming routing, splitting, merging, and processing FlowFile.

NiFi is implemented in the Java programming language and allows extensions (processors, controller services, and reporting tasks) to be implemented in Java. In addition, NiFi supports processors that execute scripts written in Groovy, Jython, and several other popular scripting languages.

If you want to know if any problems occur in a dataflow. You can check in the logs for anything interesting, it is much more convenient to have notifications pop up on the screen. If a Processor logs anything as a WARNING or ERROR, we will see a "Bulletin Indicator" show up in the top-right-hand corner of the Processor.

This indicator looks like a sticky note and will be shown for five minutes after the event occurs. Hovering over the bulletin provides information about what happened so that the user does not have to sift through log messages to find it. If in a cluster, the bulletin will also indicate which node in the cluster emitted the bulletin. We can also change the log level at which bulletins will occur in the Settings tab of the Configure dialog for a Processor.

Password is a sensitive property. Hence, while exporting the DataFlow as a template password will be dropped. As soon as you import the template in the same or different NiFi system.

A Reporting Task is a NiFi extension point that is capable of reporting and analyzing NiFi's internal metrics in order to provide the information to external resources or report status information as bulletins that appear directly in the NiFi User Interface.

Sometime what happens that Producer system is faster than consumer system. Hence, the messages which are consumed is slower. Hence, all the messages (FlowFiles) which are not being processed will remain in the connection buffer. However, you can limit the connection backpressure size either based on number of FlowFiles or number of data size. If it reaches to defined limit, connection will give back pressure to producer processor not run. Hence, no more FlowFiles generated, until backpressure is reduced.

A FlowFile is a message or event data or user data, which is pushed or created in the NiFi. A FlowFile has mainly two things attached with it. Its content (Actual payload: Stream of bytes) and attributes. Attributes are key value pairs attached to the content (You can say metadata for the content).

When a processor finishes with processing of FlowFile. It can result in Failure or Success or any other relationship. And based on this relationship you can send data to the Downstream or next processor or mediated accordingly.