Integration / Apache NiFi Interview Questions

What is a Connection in NiFi and how does back-pressure work?

A Connection in NiFi is a directed, persistent queue that links the output of one processor to the input of another. FlowFiles physically queue here when the downstream processor cannot keep up. Each connection carries one or more relationships from the upstream processor (e.g., success, failure). All processor relationships must be either connected or auto-terminated before the processor can start.

Back-pressure is configured on each connection with two independent thresholds:

Back Pressure Object Threshold: Maximum FlowFile count in the queue. When reached, the upstream processor stops being scheduled. Default is 10,000.

Back Pressure Data Size Threshold: Maximum total byte size of queued content. When exceeded, the upstream processor also pauses. Default is 1 GB.

Setting both to 0 disables back-pressure, allowing the queue to grow unbounded — use cautiously. Connections also support prioritizers controlling dequeue order: First In First Out (default), Newest First, Oldest First, or by size.

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What happens to an upstream processor when a connection's back-pressure object threshold is reached?New FlowFiles are silently discarded

✗ Try again — NiFi never silently discards FlowFiles under back-pressure; it pauses the producer.

The upstream processor stops being scheduled until the queue drains below the threshold

✓ Well done — back-pressure pauses scheduling of the upstream processor, providing natural flow control without data loss.

The processor throws an exception and enters a failed state

✗ Try again — back-pressure is normal flow control, not an error condition.

What must be true about all processor relationships before a processor can be started in NiFi?Every relationship must be connected to a downstream component or explicitly auto-terminated

✓ Well done — unhandled relationships prevent the processor from starting, ensuring no FlowFiles are silently dropped.

At least one relationship must loop back to the same processor

✗ Try again — retry loops are optional; the requirement is that all relationships are handled.

All relationships must point to the same downstream processor

✗ Try again — different relationships can go to different processors or be auto-terminated independently.

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What is Apache NiFi and what problem does it solve? What is a FlowFile in Apache NiFi? What are the three NiFi repositories and what does each store? What is a Processor in Apache NiFi and what are the main processor categories? What is a Connection in NiFi and how does back-pressure work? What is NiFi Expression Language and where can it be used? What is data provenance in Apache NiFi and how do you access it? What is a Process Group in NiFi and why is it used? What is NiFi Registry and how does it integrate with NiFi? How does NiFi clustering work and what is the role of ZooKeeper? What is a Controller Service in NiFi and how is it different from a Processor? What is the GenerateTableFetch and QueryDatabaseTable pattern for incremental database ingestion? What is the Record-based processing model in NiFi and why is it preferred? What is State Management in NiFi and what types of state scope exist? What is NiFi Site-to-Site (S2S) and when do you use it? What is NiFi and how does it relate to Apache NiFi? What is NiFi Parameter Context and how does it differ from Variables? How does NiFi handle security — TLS, authentication, and authorization? What is the NiFi NAR (NiFi Archive) classloading model? What are Reporting Tasks in NiFi and what are common use cases? How do you handle errors and failures in a NiFi flow? What is the SplitText processor and how do you control split behavior? What is the MergeContent processor and how is it used? What is the InvokeHTTP processor and what are key configuration considerations? What is the PublishKafka and ConsumeKafka processor pair and what are key configuration options? What is the ExecuteScript processor and what scripting languages does it support? What is the JoltTransformJSON processor and how do you use it? What is the PutDatabaseRecord processor and how does it differ from ExecuteSQL? What is the ListSFTP and FetchSFTP processor pattern and how does it work? What is the LookupRecord processor used for? What is the PartitionRecord processor and what is a common use case? What is the ConvertRecord processor and how is it used for format conversion? What are the NiFi processor scheduling strategies? What is the difference between EvaluateJsonPath and FlattenJson processors? How does NiFi integrate with Apache Hadoop and HDFS? What is the UpdateAttribute processor and how is its Advanced Mode used? How do you implement deduplication in a NiFi flow? What is the HandleHttpRequest and HandleHttpResponse processor pair used for? How does NiFi achieve guaranteed delivery and what are its durability guarantees? What is the Funnel component in NiFi and when do you use it? What is the difference between GetFile and ListFile + FetchFile processors? How does NiFi support schema evolution in data pipelines? What is the RouteText processor and how does it differ from RouteOnContent? What performance tuning options are available in NiFi and what are common bottleneck patterns? How does NiFi integrate with cloud storage services like Amazon S3?

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Integration / Apache NiFi Interview Questions

What is a Connection in NiFi and how does back-pressure work?

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