Integration / Apache NiFi Interview Questions

What is NiFi Site-to-Site (S2S) and when do you use it?

NiFi Site-to-Site (S2S) is a native protocol for transferring FlowFiles directly between NiFi instances — between two standalone NiFi servers, between nodes in a cluster, or between NiFi and MiNiFi agents. It operates over HTTP/HTTPS or raw TCP sockets and provides end-to-end guaranteed delivery, optional compression, and mutual TLS authentication.

S2S works through Remote Process Groups (RPGs) on the sending side. An RPG is configured with the URL of the remote NiFi instance. The sending NiFi queries the remote instance for available Input Ports, then routes FlowFiles to the chosen Input Port.

Key features of S2S:

Automatic load balancing: When the remote NiFi is a cluster, the RPG automatically distributes FlowFiles across all healthy cluster nodes using peer selection.

Back-pressure propagation: If the remote Input Port queue is full, the sender is notified and slows down — extending NiFi's back-pressure model across instance boundaries.

Compression: Optional GZIP compression reduces bandwidth between instances.

Common use cases: MiNiFi agents on edge devices pushing data to a central NiFi hub; cross-datacenter data transfer pipelines; routing data from an ingestion NiFi tier to a processing NiFi tier.

What NiFi component on the sending side is used to push FlowFiles to a remote NiFi instance via Site-to-Site?Output Port

✗ Try again — Output Ports are the exit point within a Process Group; the sending component is a Remote Process Group.

Remote Process Group (RPG)

✓ Well done — an RPG configured with the remote NiFi URL discovers its Input Ports and routes FlowFiles to them via S2S.

PutHTTP processor

✗ Try again — PutHTTP sends arbitrary HTTP requests; S2S uses the dedicated RPG component with the NiFi-native protocol.

How does Site-to-Site handle back-pressure when the remote NiFi instance's Input Port queue is full?The sender drops FlowFiles to avoid blocking

✗ Try again — NiFi never drops FlowFiles for back-pressure; it slows the sender instead.

The remote instance signals back-pressure to the sender, which slows its transfer rate accordingly

✓ Well done — S2S propagates back-pressure across instance boundaries, extending NiFi's flow control model end-to-end.

The connection between instances is terminated and must be manually re-established

✗ Try again — S2S handles back-pressure gracefully without dropping connections.

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Integration / Apache NiFi Interview Questions

What is NiFi Site-to-Site (S2S) and when do you use it?

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