Sentinel Applications and Yield

A MiNiFi C++ sentinel is the YuniKorn Application: 1:1 with a schedulable process. signals-ui Applications lists only what YK admitted.

Closed loop

YK ends Application  →  last-gasp / heartbeat (C2 HTTP)
                     →  Signals C2
                     →  gRPC zndx.engine.v1.Engine/Yield
                     →  owning engine ends the local process

Two wires on the C2 process: HTTP toward sentinels; gRPC Yield toward the lattice engine from peer-contract.json. Sentinels never dial gRPC.

Unknown workload_id is idempotent (ok=true, process_ended=false).

Resource claim

The Application’s resource vector is the claim. GPU work asks for federation.zndx.org/gpu on the sentinel (or on an in-cluster pod). That is how YK sees occupancy and how preemption frees a card. CUDA still runs on the host engine unless the work is an in-cluster GPU pod (nvidia.com/gpu and the federation token). Do not request nvidia.com/gpu on a CPU-only MiNiFi container.

Queue path is the resource class (root.internal.inference.extract, root.internal.compute, …), not root.{project}. Project stays on federation.project for C2 and Yield.

Platform warehouse upkeep (data-product.tier-upkeep) uses a flow-level proxy sentinel on root.platform (signals-dataproduct-tier-upkeep) when the Metaflow run is not itself a YK Application. A @kubernetes step is an Application — same app-id / workload_id.

What this cut is not

• NiFi proper / canvas (optional later K8s fielding for OTel wiring; not signals-ui)
• Per-engine C2 servers
• Gaius/Aegir/Atelier Yield bodies (they implement the same RPC; Gaius maps onto CompleteWorkload / restore)
• Moving host vLLM into the sentinel container

Unit

signals-c2.service is foundation (with the engine): signals.target Wants it; it After= signals-engine.service. Start/stop wrappers: scripts/systemd_c2_{start,stop}.sh.

sudo systemctl start signals-c2.service   # or: start signals.target
curl -sf http://127.0.0.1:50561/healthz

just signals-ready records C2 as WARN until the unit is up (C2 starts after ready).

Lab

# engine on :50551, control :50552, C2 :50561
just sentinel-yield-lab

Protocol: components/signals-protocol Engine/Yield. Ops design: specification/operations/minifi_sentinels.md.