Integration / Apache NiFi Interview Questions

What is the difference between GetFile and ListFile + FetchFile processors?

Both approaches ingest files from a local filesystem, but they differ in architecture, parallelism, and operational characteristics.

GetFile: The older, simpler, single-processor approach. It lists a directory, picks up files matching the configured filter, moves or deletes the source file atomically, and produces a FlowFile with the file content. Critical limitation: it is not safe to run with multiple concurrent tasks because two threads could attempt to process the same file simultaneously — its filesystem rename locking is not atomic on all filesystems or NFS mounts. On a cluster, GetFile should run on the Primary Node only.

ListFile + FetchFile: The modern, recommended approach. ListFile scans the directory and emits one FlowFile per found file containing only metadata attributes (filename, path, size, last modified). It uses State Management to track already-listed files. FetchFile then reads the actual file content from disk. This separation enables:

Parallel fetching: multiple concurrent FetchFile tasks read files simultaneously
Clear separation of concerns: listing happens once; fetching can be retried independently per file
Works correctly in clustered NiFi without Primary Node restriction on the fetch step

GetFile remains appropriate for simple single-node use cases. For new development and cluster deployments, ListFile + FetchFile is preferred.

Why is GetFile not recommended for use with multiple concurrent tasks in a NiFi cluster?Multiple threads could attempt to process the same file simultaneously; its filesystem-rename locking is not reliable in all environments

✓ Well done — GetFile's rename-based file locking is not guaranteed atomic on all filesystems, especially NFS, leading to potential duplicate processing.

GetFile does not support HDFS filesystems

✗ Try again — that is a separate concern; the cluster concurrency problem is about race conditions on file locking.

GetFile produces FlowFiles without filename attributes

✗ Try again — GetFile does set filename and path attributes; the limitation is concurrency safety.

What mechanism does ListFile use to avoid re-listing files it has already seen on subsequent runs?It moves processed files to a separate archive directory

✗ Try again — ListFile does not move or modify source files; it is read-only.

NiFi State Management — it persists the last seen file timestamp or set of seen filenames

✓ Well done — ListFile uses the State Management API to durably record which files have been listed, surviving processor restarts.

A Distributed Map Cache populated with each file inode number

✗ Try again — ListFile uses NiFi's built-in State Management, not an external Distributed Map Cache.

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Integration / Apache NiFi Interview Questions

What is the difference between GetFile and ListFile + FetchFile processors?

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