# SA/MR Deployment Topology

**SA** is the name of the whole system pictured in `grand_plan.jpg`: two
chains of independent, single-function NiFi hosts (each host linked to the
next via Site-to-Site) bridged in the middle by **MR**.

**MR** is the one-way relay (diode-style boundary) between the two chains
— forward error correction via an HTTP service, ~1GB target chunk size, no
return channel for retransmission requests.

Content flows one direction through SA: external S3/S2S in -> first NiFi
chain (node 1 -> 2 -> 3) -> MR -> second NiFi chain (node 1 -> 2 -> 3) ->
external S3/S2S out. The Replay DB branches off **before** MR, via a
"copy" from node 1 of the *first* chain — i.e. at the true ingest point
into SA, not after delivery. This was a real correction during design
review — an earlier draft had the Replay DB positioned after MR, which was
wrong.

Chunking and hashing both happen at that same ingest point (node 1 of the
first chain), in a single streaming pass, so the same chunked
representation transits both the intra-chain S2S hops and the MR relay
uniformly — no separate chunking scheme per transport, and no size
threshold decides whether to chunk (a small file is just the one-chunk
case).

Source: whiteboard sketch `grand_plan.jpg`, reconciled into
`docs/superpowers/specs/2026-07-28-flowfile-packaging-signing-design.md`.