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docs(mesh): Phase 2 plan — comm actors + ClusterClient transport

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Phase 2 of the per-cluster mesh program: move the three central->node command
channels (deployments, driver-control, alarm-commands) and the deployment-acks
reply channel off DistributedPubSub onto Akka ClusterClient, behind a config
flag.

Recon of both repos turned up three corrections to the design doc's account of
the sister project, all folded into the plan:

- Design doc S2 claims "every unhandled message replies with a typed failure".
  ScadaBridge has no ReceiveAny/Unhandled override in either comm actor; the
  typed-failure idiom fires only for a MISSING REGISTRATION, per message type.
- "No central buffering" was never a setting they wrote. They have zero
  akka.cluster.client HOCON and run the defaults (buffer-size 1000,
  reconnect-timeout off). We choose buffer-size = 0 deliberately.
- Publish -> Send is the wrong substitution. Today's deploy notify is a
  broadcast every DriverHostActor receives (no ClusterId filter exists on the
  node side), so it must become SendToAll. Send would deploy to exactly one
  node of the fleet and seal green on partial acks.

Also records the single-mesh duplicate-delivery trap (one ClusterClient in
Phase 2, not one per Cluster -- a receptionist serves its whole mesh) and one
deviation from the program plan's exit gate: there is no cross-boundary Ask in
Phase 2, because every migrated command is fire-and-forget with a local reply,
so "an Ask timing out cleanly" cannot be run as written.

Marks the program tracking tables current: prereq + Phase 1 are DONE (they
still read "not executed"), Phase 2 in progress.

Claude-Session: https://claude.ai/code/session_01GASWkNEi68FSCtvr6rLoEW
This commit is contained in:
Joseph Doherty
2026-07-22 10:37:37 -04:00
parent 7654f24dab
commit 1ec831883c
4 changed files with 1019 additions and 6 deletions
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docs/plans/2026-07-22-per-cluster-mesh-program.md
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@@ -198,9 +198,9 @@ resource sizing on the site VMs should be checked once both products run the ful
|---|---|
| 0a downing strategy | DONE 2026-07-21 (live gate → Phase 7) |
| 0b oldest-Up election | DONE 2026-07-21 |
| Prereq: selfform-fallback + manual-failover plan | plan written 2026-07-22, not executed |
| 1 ClusterNode columns + DB ack set | **detailed plan ALREADY WRITTEN** (`2026-07-21-per-cluster-mesh-phase1.md`, from the design session — do NOT write a new one), not executed. ⚠ Carries a decision gate: DB-derived expected-ack set changes deploy-seal semantics (a stopped-but-enabled node now FAILS the deploy at the apply deadline instead of sealing green without it; escape hatch = `ClusterNode.Enabled=0`) — confirm with the owner before its Task 3. |
| 2 ClusterClient transport | not started |
| Prereq: selfform-fallback + manual-failover plan | **DONE 2026-07-22**, merged `a78425ea`. Shipped *not* as the planned `SelfFormAfter` watchdog — the live gate caught that islanding a manually-failed-over node — but as self-first seed ordering + `AkkaClusterOptionsValidator`. Phase 6's seed-ordering scope is therefore already discharged. |
| 1 ClusterNode columns + DB ack set | **DONE 2026-07-22**, merged `7654f24d`. Deploy-seal semantics changed as flagged, but the escape hatch is **`ClusterNode.MaintenanceMode`**, not `Enabled=0` — the live gate found `Enabled=0` is rejected by `DraftValidator.ValidateClusterTopology` on any 2-node pair. Gate record: `2026-07-22-mesh-phase1-live-gate.md`. |
| 2 ClusterClient transport | **IN PROGRESS** — plan being written 2026-07-22 |
| 3 fetch-and-cache | not started |
| 4 cut driver ConfigDb | not started |
| 5 gRPC telemetry | not started |