Joseph Doherty
91fb2b48dd
SPEC 2.4 named OtOpcUa and MxGateway as users; neither is (verified against every app's default branch; MxGateway worker IPC is named pipes, OtOpcUa deliberately does not gate readiness on gateway channels). Keep the check (removal is a breaking API change; small, tested building block), mark it as no-current-consumers in SPEC 2.4/6/7, both READMEs, the shared-contract doc and GAPS. Claude-Session: https://claude.ai/code/session_01GT67AEHd2Acv1YPwGfXEoV
84 lines
4.8 KiB
Markdown
84 lines
4.8 KiB
Markdown
# Health (readiness / liveness / active-node)
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Second normalized component under the operability cluster. **Goal: path to shared code** — converge
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the three sister projects onto a common three-tier health endpoint convention and a set of shared
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probe implementations, proposed as the `ZB.MOM.WW.Health` library set (3 packages), while each
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project keeps its own probe registration and orchestrator wiring.
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- The one target: [`spec/SPEC.md`](spec/SPEC.md)
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- The proposed shared library: [`shared-contract/ZB.MOM.WW.Health.md`](shared-contract/ZB.MOM.WW.Health.md)
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- Divergences + backlog: [`GAPS.md`](GAPS.md)
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- Current state, per project: [`current-state/`](current-state/)
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## Why health is a strong normalization candidate
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Both OtOpcUa and ScadaBridge trace their health-check structure to the same "ScadaLink three-tier
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pattern" (`HealthEndpoints.cs:13` says so explicitly) but have already diverged in probe logic,
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status semantics, response writer, and endpoint registration style. MxAccessGateway has no shared
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ancestry here — it has a single hardcoded `/health/live` endpoint with no real probes at all.
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The common core (three tiers, database probe, Akka cluster probe, active-node probe) is
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re-implemented twice and absent once. Shared probe implementations with configurable policies
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close the gap without forcing identical behavior onto projects with legitimately different cluster
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semantics.
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## Status by project
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**Adopted by all four apps at `0.3.0`; probe coverage re-verified 2026-11-09 (scadaproj#11).** Every app
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calls `MapZbHealth()` (`/healthz`, `/health/ready`, `/health/active`, canonical JSON). The per-endpoint
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coverage matrix, SPEC deviations and remaining gaps are in [`GAPS.md`](GAPS.md); code-verified detail per
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app (OtOpcUa, MxAccessGateway, ScadaBridge, HistorianGateway) is in
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[`current-state/<project>/CURRENT-STATE.md`](current-state/). The "Why" section above and the bullets
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below describe the original 2026-06 design rationale.
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## Normalized vs. left per-project
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**Normalized (the shared target):**
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- Three-tier endpoint convention: `/health/ready` (tag `ready`), `/health/active` (tag `active`),
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`/healthz` (bare liveness). Mapped by `app.MapZbHealth()` from `ZB.MOM.WW.Health`.
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- Canonical JSON response writer (lifted from `HealthChecks.UI.Client` style; no per-project
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writer wiring needed).
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- `IActiveNodeGate` seam — generalized from ScadaBridge's `ActiveNodeGate`; wired into `MapZbHealth`
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for automatic active-tier response.
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- `GrpcDependencyHealthCheck` — reachability probe for a downstream gRPC dependency. Shipped but
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**currently has no consumers** (neither OtOpcUa nor MxAccessGateway adopted it; scadaproj#28).
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- `AkkaClusterHealthCheck` (in `ZB.MOM.WW.Health.Akka`) with a configurable status policy.
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Default = ScadaBridge's three-way policy; `OtOpcUaCompat` preset preserves OtOpcUa's two-way
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self-Up-among-members scan.
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- `ActiveNodeHealthCheck` (in `ZB.MOM.WW.Health.Akka`) with an optional role filter. Role-less =
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ScadaBridge's behavior (Up + cluster leader); role-filtered = OtOpcUa's `AdminRoleLeader`
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behavior.
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- `DatabaseHealthCheck<TContext>` (in `ZB.MOM.WW.Health.EntityFrameworkCore`) with default
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`CanConnectAsync` and an optional `ProbeQuery` delegate.
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- `AllowAnonymous` on all three tiers by default (consistent across all three projects today).
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**Left per-project (not forced together):**
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- Which probes each app registers, their names, and which tags they carry.
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- Orchestrator / Traefik wiring (sidecars, route rules, upstreams).
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- ScadaBridge's `HealthMonitoring/` distributed aggregation pipeline (`SiteHealthCollector`,
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`CentralHealthAggregator`, `HealthReportSender`, etc.) — domain-specific, no shared-library
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equivalent.
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- MxAccessGateway's `GatewayHealthReply` metadata (`DefaultBackend`, `WorkerProtocolVersion`) —
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keep as a bespoke `/info` endpoint.
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- The x86 worker process — out of process and out of scope; the gateway-side
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no probe observes it directly (worker IPC is named pipes, not gRPC).
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## Package structure
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`ZB.MOM.WW.Health` ships as three dependency-split packages:
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| Package | Contents | Consumers |
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|---|---|---|
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| `ZB.MOM.WW.Health` | Core tiers, `MapZbHealth`, canonical writer, `IActiveNodeGate`, `GrpcDependencyHealthCheck` (no consumers) | All three |
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| `ZB.MOM.WW.Health.Akka` | `AkkaClusterHealthCheck` + status presets, `ActiveNodeHealthCheck` + role filter | OtOpcUa, ScadaBridge |
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| `ZB.MOM.WW.Health.EntityFrameworkCore` | `DatabaseHealthCheck<TContext>` + optional probe delegate | OtOpcUa, ScadaBridge |
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MxAccessGateway consumes the core package only (no Akka, no EF). OtOpcUa and ScadaBridge consume
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all three.
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## Component status
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**Status: Adopted — library at 0.3.0** ([`../../ZB.MOM.WW.Health/`](../../ZB.MOM.WW.Health/), 3 packages),
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pinned by all four apps; coverage re-verified 2026-11-09. Remaining gaps: [`GAPS.md`](GAPS.md).
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