# Code Review — Health

| Field | Value |
|-------|-------|
| Library | `ZB.MOM.WW.Health/` |
| Packages | `ZB.MOM.WW.Health`, `ZB.MOM.WW.Health.Akka`, `ZB.MOM.WW.Health.EntityFrameworkCore` |
| Component spec | `components/health/spec/SPEC.md` |
| Shared contract | `components/health/shared-contract/ZB.MOM.WW.Health.md` |
| Status | Reviewed |
| Last reviewed | 2026-11-09 (re-review; baseline 2026-06-01 at `5f75cd4`) |
| Reviewer | Claude (2026-11-09 re-review, scadaproj#15; baseline: Claude automated) |
| Commit reviewed | `91fb2b4` |
| Open findings | 0 |

## Summary

**2026-11-09 re-review (`91fb2b4`, scadaproj#15).** Re-reviewed at `91fb2b4` (2026-11-09) against the 2026-06-01 baseline `5f75cd4`; the library is now
`0.3.0`. The headline change, the active tier now meaning "oldest `Up` member" through the new
`ClusterActiveNode` helper instead of `Leader`/`RoleLeader`, is correct. Only `MemberStatus.Up` members
are eligible, so `Joining`, `WeaklyUp`, `Leaving`, `Exiting`, `Down` and `Removed` are all excluded. Ties
fall through to Akka's `Member.IsOlderThan`, which breaks an equal up-number on address ordering, so the
choice is deterministic. Self-identity is compared on `UniqueAddress`, so a restarted incarnation on the
same host and port is never mistaken for the old one. An `Up`-but-unreachable oldest member is still
named active, which matches singleton placement until the split-brain resolver downs it. A role-scoped
node that carries none of the preferred roles answers `NoActiveRoleStatus` (default Unhealthy, i.e. 503).
Both startup-safety paths (no `ActorSystem`, cluster not yet accessible) still return Degraded (200), and
a container-built `AddCheck<ActiveNodeHealthCheck>` probe confirmed that `ActivatorUtilities` picks the
right constructor out of the three. The status mapping, the `data` JSON shape (emitted only when the
check supplies data, `description` always present) and the composite convention builder are correct.
All 76 tests pass (Health.Tests 25, Health.Akka.Tests 45, Health.EntityFrameworkCore.Tests 6).
`ClusterActiveNodeTests` runs a real two-node cluster whose age order and address order diverge, and
covers role scoping, role preference and the gate. The non-`Up` exclusions (`Leaving`/`WeaklyUp`/
`Joining`) and the restart-incarnation `UniqueAddress` comparison are verified by reading the code only:
no test exercises them. That is a test gap, not a defect. There is one new Low finding: the `AkkaActiveNodeGate` can only be scoped to a
single role, while the probe takes an ordered role-preference list. So the documented "gate and probe
can never disagree" guarantee does not hold for the fused-node configuration that OtOpcUa actually runs
(Health-007). It is latent, because no family app uses `AkkaActiveNodeGate` today.

**2026-06-01 baseline (`5f75cd4`).** The library is small, cohesive, and well-documented, and it tracks the normalized spec closely:
the three-tier endpoint convention, the canonical JSON writer, the `IActiveNodeGate` seam, the
configurable `AkkaClusterStatusPolicy` presets, and the role-filtered `ActiveNodeHealthCheck` all
match the contract. The package split is clean — Akka and EF Core stay out of the core package, so
MxGateway can take core only (category 8: no leakage). The decision logic is factored into pure,
exhaustively table-tested functions (`AkkaClusterStatusPolicy`, `ActiveNodeDecision`), and the test
suite (58 tests) exercises the public surface through a real TestServer / real SQLite / real probe
delegates rather than mocks.

The findings cluster around **error-handling completeness in the health-check probes** (category 4),
the highest-risk area for this library: a probe that throws past the `IHealthCheck` boundary, or that
returns a status the spec says it should not, degrades the value of every consuming app's `/health/*`
endpoints. The two Akka checks and the gRPC check do not guard the cluster-state / probe call the way
the spec requires (return Degraded on inaccessible cluster) or the way the sibling `DatabaseHealthCheck`
does (catch-all → Unhealthy). The framework's `HealthCheckService` catches escaping exceptions, so none
of these crash an endpoint — that caps their severity at Medium — but they produce a result that
disagrees with the documented contract. The remainder are Low: a JSON shape nuance (`description` key
omitted vs. emitted-null), recommended-tag drift in XML docs, a return-value footgun in `MapZbHealth`,
and missing `GenerateDocumentationFile` so the (otherwise excellent) XML docs do not ship in the nupkgs.

## Checklist coverage

2026-11-09 re-review at `91fb2b4`:

| # | Category | Examined | Notes |
|---|----------|----------|-------|
| 1 | Correctness & logic bugs | ☑ | `OldestUpMember`/`SelfIsActive`/`ResolveActiveRole` are correct for ties, non-Up states, role scoping, the no-Up-member case (Unhealthy) and restart incarnations (`UniqueAddress`). Gate/probe scope mismatch → Health-007. |
| 2 | Public API surface & compatibility | ☑ | 0.3.0 is a deliberate, documented behaviour break (standby 503, role-lacking node Unhealthy). `ActiveNodeDecision` was removed but was internal. New public `ClusterActiveNode` and `ActiveNodeHealthCheckOptions` are sealed/static and nullable-correct. The gate offers a single `role` where the probe offers `RolePreference` → Health-007. |
| 3 | Concurrency & thread safety | ☑ | Checks and gate hold no mutable state. Membership is read from a single `ClusterReadView` snapshot per call. No issues found. |
| 4 | Error handling & resilience | ☑ | Health-001/002 fixes hold: cluster access is wrapped and maps to Degraded (OCE excluded); the gate swallows to `false`. No issues found. |
| 5 | Security & secret handling | ☑ | Endpoints are anonymous by design. The `data` payload carries node addresses, roles and counts only. No issues found. |
| 6 | Performance & resource management | ☑ | One linear member scan per probe. No allocations of note and nothing disposable. No issues found. |
| 7 | Spec & shared-contract adherence | ☑ | Three tiers, status strings and JSON envelope match SPEC §3. The oldest-Up rule matches both Akka apps (OtOpcUa `RedundancyStateActor` and ScadaBridge `ActiveNodeEvaluator` delegate to it). No issues found. |
| 8 | Packaging, dependencies & project layout | ☑ | Version 0.3.0; Akka stays out of the core package. The NU1510 warning (explicit `HealthChecks.Abstractions` reference is now prunable) is cosmetic. No issues found. |
| 9 | Testing coverage | ☑ | 76 tests pass, including real-cluster `ClusterActiveNodeTests` (age order diverging from address order), startup safety, role resolution and the `data` writer shape. Untested: the `Leaving`/`WeaklyUp`/`Joining` exclusion and same-address restart incarnations (correct by code reading). A container-built `AddCheck<ActiveNodeHealthCheck>` was probed in the scratchpad and resolves correctly (Degraded with no ActorSystem). |
| 10 | Documentation & XML docs | ☑ | Thorough and accurate, apart from the gate's "can never disagree" claim (Health-007). |

<details><summary>2026-06-01 baseline checklist (<code>5f75cd4</code>)</summary>

| # | Category | Examined | Notes |
|---|----------|----------|-------|
| 1 | Correctness & logic bugs | ☑ | Tier predicates, policy presets, and `ActiveNodeDecision` matrices are correct and match the spec tables. No logic defects found. |
| 2 | Public API surface & compatibility | ☑ | Health-005. Surface is minimal, sealed, well-named; nullable annotations correct; no internal types leak (`ActiveNodeDecision` is `internal`). |
| 3 | Concurrency & thread safety | ☑ | Options are mutable POCOs but per-registration; checks hold no shared mutable state; cluster-state reads are snapshot reads; static writer options are immutable. No issues found. |
| 4 | Error handling & resilience | ☑ | Health-001, Health-002. Akka checks don't guard cluster-state access; gRPC check lets non-Rpc/non-OCE exceptions escape. |
| 5 | Security & secret handling | ☑ | No secrets/PII. Exception objects attached to `HealthCheckResult` (standard); endpoints `AllowAnonymous` by design. No issues found. |
| 6 | Performance & resource management | ☑ | `DatabaseHealthCheck` is pool-safe and eagerly releases the timeout timer; scopes/contexts disposed via `await using`; channel not owned (correctly not disposed). No issues found. |
| 7 | Spec & shared-contract adherence | ☑ | Health-001, Health-003, Health-004. Endpoint convention + status strings otherwise match §3. |
| 8 | Packaging, dependencies & project layout | ☑ | Health-006. Dependency split correct; central versions; net10.0; correct package ids. |
| 9 | Testing coverage | ☑ | Strong: TestServer tier tests, real SQLite EF tests, table-driven policy/decision tests, gRPC probe + timeout + cancellation. Gaps noted inline in findings, not raised separately. |
| 10 | Documentation & XML docs | ☑ | Health-004, Health-006. Public API XML docs are thorough and accurate; the issues are recommended-tag drift and docs not being packed. |

</details>

## Findings

### Health-001 — Akka health checks throw (instead of returning Degraded) when cluster state is inaccessible

| | |
|--|--|
| Severity | Medium |
| Category | Error handling & resilience |
| Status | Resolved |
| Location | `ZB.MOM.WW.Health/src/ZB.MOM.WW.Health.Akka/AkkaClusterHealthCheck.cs:45`, `ZB.MOM.WW.Health/src/ZB.MOM.WW.Health.Akka/ActiveNodeHealthCheck.cs:106` |

**Description**

Both Akka checks guard only the *null* ActorSystem case: `_serviceProvider.GetService<ActorSystem>()`
returns `null` → Degraded. But once a non-null `ActorSystem` is resolved they call `Cluster.Get(system)`
and read `.SelfMember` / `.State.Leader` with no try/catch. The spec is explicit that this path must be
Degraded, not an exception:

> "in both modes, if the ActorSystem is not yet ready **or cluster state is inaccessible** (e.g.
> during startup), the check returns Degraded (startup-safety rule)." — `SPEC.md` §2.2 note.

`Cluster.Get(system)` throws (`ConfigurationException`) when the `Akka.Cluster` extension is not
configured on the resolved ActorSystem, and `SelfMember` can throw during the window where the
ActorSystem object exists but the cluster has not finished initialising — exactly the startup race the
spec calls out. The ActorSystem being present-but-not-yet-clustered is a very real ordering in a
`Microsoft.Extensions.Hosting` app (the ActorSystem is registered in DI before `Cluster` has joined).

The escaping exception is caught by ASP.NET Core's `HealthCheckService`, which records the entry as
Unhealthy — so the endpoint does not crash. But Unhealthy on the `ready` tier returns **503** and
removes the node from load-balancing, whereas the spec's intended Degraded returns **200** (still in
rotation). A transient startup window therefore yanks a healthy-but-starting node out of rotation,
the opposite of the "startup-safe" guarantee the XML docs advertise.

**Recommendation**

Wrap the cluster-state read in a try/catch and return `HealthCheckResult.Degraded(...)` on failure, so
both the null-ActorSystem and inaccessible-cluster paths converge on Degraded as the spec requires:
resolve `Cluster.Get(system)` and read membership inside a `try`, catching the cluster extension's
startup exceptions and mapping them to Degraded with a "cluster not yet ready" description.

**Resolution**

Resolved in `544a6dd`, 2026-06-01 — wrapped the `Cluster.Get(system)`/`SelfMember`/leader reads in `AkkaClusterHealthCheck` and `ActiveNodeHealthCheck` in `try/catch (Exception when not OCE)` returning `Degraded("Akka cluster state not yet accessible.")`; tests add a plain non-clustered ActorSystem to assert Degraded instead of the escaping `ConfigurationException`.

### Health-002 — `GrpcDependencyHealthCheck` lets non-`RpcException`/non-`OperationCanceledException` errors escape

| | |
|--|--|
| Severity | Medium |
| Category | Error handling & resilience |
| Status | Resolved |
| Location | `ZB.MOM.WW.Health/src/ZB.MOM.WW.Health/GrpcDependencyHealthCheck.cs:54` |

**Description**

`CheckHealthAsync` catches only `RpcException` and `OperationCanceledException`. Any other exception
thrown by the probe escapes the method. This is reachable on both paths:

- Default probe: `GrpcChannel.ConnectAsync` can throw exceptions other than `RpcException` —
  e.g. `InvalidOperationException` (channel/socket misuse, shutdown) or `HttpRequestException` /
  `SocketException` surfaced from the transport before a gRPC status is produced.
- Custom probe (`GrpcDependencyOptions.Probe`): a caller-supplied delegate (e.g. a
  `grpc.health.v1.Health/Check` RPC built on a non-gRPC client) can throw anything.

The XML docs and shared contract describe the result as Unhealthy "when it returns `false`, throws an
`RpcException`, or times out" — they do not promise to handle arbitrary exceptions, and the code does
not. By contrast the sibling `DatabaseHealthCheck` has a catch-all `catch (Exception ex)` →
`Unhealthy("Database connection failed.", ex)` (`DatabaseHealthCheck.cs:78`), so the two probes are
asymmetric. As with Health-001 the framework's `HealthCheckService` records the escaping exception as
Unhealthy, so no endpoint crashes — but the dependency-named, controlled description
(`"{name} probe failed…"`) is lost, and the library violates its own "must not throw past the
`IHealthCheck` boundary" intent.

**Recommendation**

Add a trailing `catch (Exception ex)` returning `HealthCheckResult.Unhealthy($"{name} probe failed:
{ex.Message}", ex)`, after the existing OCE/Rpc handlers (so external cancellation still propagates).
This brings the gRPC probe in line with `DatabaseHealthCheck` and the documented contract.

**Resolution**

Resolved in `544a6dd`, 2026-06-01 — added a trailing `catch (Exception ex)` to `GrpcDependencyHealthCheck.CheckHealthAsync` returning `Unhealthy("{name} probe failed: {ex.Message}", ex)` after the OCE/Rpc external-cancellation handlers; new test asserts a probe throwing `InvalidOperationException` maps to Unhealthy.

### Health-003 — Null `description` is omitted from the JSON body instead of emitted as `null`

| | |
|--|--|
| Severity | Low |
| Category | Spec & shared-contract adherence |
| Status | Resolved |
| Location | `ZB.MOM.WW.Health/src/ZB.MOM.WW.Health/ZbHealthWriter.cs:32` |

**Description**

`SerializerOptions` sets `DefaultIgnoreCondition = JsonIgnoreCondition.WhenWritingNull`, so a check that
produces no description renders an entry with **no** `description` key at all:
`{ "status": "Healthy", "durationMs": 0.1 }`. The spec models `description` as a `string?` that "may be
null" and both the canonical example (`SPEC.md` §3) and the `HealthChecks.UI.Client` shape the writer
claims to mirror emit the key with a `null` value rather than dropping it. Consumers/dashboards parsing
the body and reading `entries.<name>.description` must therefore handle a *missing* property, not just a
null one. The deviation is undocumented and untested — `ResponseWriterTests` only asserts the
present-description case.

Low because the aggregate `status`/HTTP-code contract that orchestrators key on is unaffected; only the
descriptive sub-field shape drifts.

**Recommendation**

Either remove `WhenWritingNull` (so `description: null` is emitted, matching the spec example and the
UI-client shape), or document explicitly in the writer's XML docs and `SPEC.md` §3 that absent
descriptions are omitted, and add a test pinning the chosen behaviour.

**Resolution**

Resolved in `544a6dd`, 2026-06-01 — removed `DefaultIgnoreCondition = WhenWritingNull` from `ZbHealthWriter.SerializerOptions` so a null `description` renders as `"description": null` (matching the spec example / UI-client shape); writer XML doc now states the key is always present, and a new `ResponseWriterTests` case pins present-and-null.

### Health-004 — XML docs recommend the `active` tag for ready-tier probes, contradicting the spec

| | |
|--|--|
| Severity | Low |
| Category | Documentation & XML docs |
| Status | Resolved |
| Location | `ZB.MOM.WW.Health/src/ZB.MOM.WW.Health.Akka/AkkaClusterHealthCheck.cs:11`, `ZB.MOM.WW.Health/src/ZB.MOM.WW.Health/GrpcDependencyHealthCheck.cs:21` |

**Description**

`AkkaClusterHealthCheck`'s summary says *"Register to the `ZbHealthTags.Ready` tag (recommended
`[ready, active]`)"*, and `GrpcDependencyHealthCheck` likewise recommends tagging `[ready, active]`.
The spec is unambiguous that both probes belong to the `ready` tier only: §2.2 "Registered to the
`ready` tag" (Akka cluster) and §2.4 "Registered to the `ready` tag" (gRPC dependency). The `active`
tier is reserved by §1 / §2.3 for the leader/active-singleton probe (`ActiveNodeHealthCheck`); putting
cluster-membership or gRPC-reachability checks on the `active` tier pollutes the active-node tier with
non-leadership concerns and contradicts the convergence convention the library exists to enforce.

**Recommendation**

Bring the XML-doc recommendations in line with the spec — recommend `ZbHealthTags.Ready` only for both
probes (drop the `active` suggestion); or, if the dual-tag recommendation is intentional, reconcile it
back into `SPEC.md` §2.2/§2.4 so code and spec agree.

**Resolution**

Resolved in `544a6dd`, 2026-06-01 — updated the XML summaries on `AkkaClusterHealthCheck` and `GrpcDependencyHealthCheck` to recommend `ZbHealthTags.Ready` only (dropped the `[ready, active]` suggestion), aligning the docs with SPEC §2.2/§2.4.

### Health-005 — `MapZbHealth` returns only the readiness builder, silently dropping conventions for the active/live tiers

| | |
|--|--|
| Severity | Low |
| Category | Public API surface & compatibility |
| Status | Resolved |
| Location | `ZB.MOM.WW.Health/src/ZB.MOM.WW.Health/ZbHealthEndpointExtensions.cs:64` |

**Description**

`MapZbHealth` maps three endpoints but returns the `IEndpointConventionBuilder` for `/health/ready`
only. Any convention a caller chains onto the result — `.RequireHost(...)`, `.RequireAuthorization()`,
`.WithMetadata(...)`, `.CacheOutput()` — applies to the readiness endpoint **alone**; the active and
liveness endpoints silently do not receive it. The behaviour is documented in the XML `<returns>`, so
this is a deliberate, disclosed trade-off rather than a bug, but it is a real footgun: the most natural
reading of `endpoints.MapZbHealth().RequireHost("…")` is "gate all three health endpoints", and the
result type gives the caller no signal that two of the three are excluded.

**Recommendation**

Consider returning a composite builder that fans conventions out to all three endpoints (collect the
three `IEndpointConventionBuilder`s and wrap them) so chained conventions behave as a caller expects.
If the single-builder return is kept for simplicity, strengthen the `<returns>` remark to a warning and
note it in the README's `MapZbHealth` example.

**Resolution**

Resolved in `544a6dd`, 2026-06-01 — `MapZbHealth` now returns a private `CompositeEndpointConventionBuilder` that fans `Add`/`Finally` to all three endpoint builders (readiness, active, liveness); `<returns>` docs updated, and a new `TierMappingTests` case proves `.RequireHost(...)` gates all three tiers.

### Health-006 — XML documentation is not emitted into the packed nupkgs

| | |
|--|--|
| Severity | Low |
| Category | Packaging, dependencies & project layout |
| Status | Resolved |
| Location | `ZB.MOM.WW.Health/Directory.Build.props:3`, `ZB.MOM.WW.Health/src/ZB.MOM.WW.Health/ZB.MOM.WW.Health.csproj:3` |

**Description**

Every public type and member in all three packages carries thorough, accurate XML documentation, but no
project (and neither `Directory.Build.props` nor the three `.csproj` files) sets
`<GenerateDocumentationFile>true</GenerateDocumentationFile>`. As a result `dotnet pack` produces nupkgs
that contain the DLLs but **no `.xml` doc files**, so consumers of `ZB.MOM.WW.Health` / `.Akka` /
`.EntityFrameworkCore` get no IntelliSense summaries or parameter docs for the API. For a shared library
whose value proposition is a documented common surface across three apps, this discards the
documentation effort at the package boundary. (It also means the compiler does not enforce the
"public members are documented" invariant via CS1591.)

**Recommendation**

Set `<GenerateDocumentationFile>true</GenerateDocumentationFile>` once in `Directory.Build.props` so all
three packable projects emit and pack their XML docs. Optionally pair with targeted `<NoWarn>` if any
CS1591 warnings surface on currently-undocumented members.

**Resolution**

Resolved in `544a6dd`, 2026-06-01 — set `<GenerateDocumentationFile>true</GenerateDocumentationFile>` (plus `NoWarn=CS1591` for test/non-packed members) in `Directory.Build.props`; verified `dotnet pack -c Release` now ships `lib/net10.0/*.xml` in all three nupkgs.

<!-- 2026-11-09 re-review (scadaproj#15) findings below. -->

### Health-007 — `AkkaActiveNodeGate` cannot express the probe's `RolePreference`, so gate and `/health/active` can disagree despite the documented guarantee

| | |
|--|--|
| Severity | Low |
| Priority | P3 |
| Category | Public API surface & compatibility |
| Status | Resolved |
| Location | `ZB.MOM.WW.Health/src/ZB.MOM.WW.Health.Akka/AkkaActiveNodeGate.cs:46` (ctor `string? role`), `:14-17` (doc claim), vs `ZB.MOM.WW.Health/src/ZB.MOM.WW.Health.Akka/ActiveNodeHealthCheck.cs:114-115` |

**Description**

In 0.3.0 `ActiveNodeHealthCheck` resolves its scope from an ordered `RolePreference` list through
`ClusterActiveNode.ResolveActiveRole(self.Roles, …)`, so a fused node answers for `admin` and a
driver-only node answers for `driver`. `AkkaActiveNodeGate` accepts only a single fixed `string? role`
and calls `ClusterActiveNode.SelfIsActive(cluster, _role)` directly. Its XML remarks still promise that
"an endpoint gated by this type and the `/health/active` probe an orchestrator routes by can never
disagree about which node is in charge". That holds only when the probe is configured with zero or one
role. For the multi-role preference (the exact configuration OtOpcUa's `HealthEndpoints` uses,
`[admin, driver]`) no gate configuration matches the probe on every node.

**Failure scenario**

An app wires `/health/active` with `RolePreference = ["admin","driver"]` and gates its
`RequireActiveNode()` endpoints with `new AkkaActiveNodeGate(sp, "admin")`. On a driver-only pair, the
oldest `driver` member answers `/health/active` 200, so the load balancer routes traffic to it. The gate
evaluates the `admin` scope: the node has no `admin` role, so `SelfIsActive` returns false and every
gated request gets 503 from `ActiveNodeGateEndpointFilter`. The pair serves nothing. Using
`new AkkaActiveNodeGate(sp)` (unscoped) instead makes the gate follow the oldest member of the whole
mesh, which on a mixed mesh can be a different node from the probe's role-scoped answer. Today this is
latent: no family app constructs `AkkaActiveNodeGate`, because ScadaBridge and OtOpcUa use their own
evaluators over `ClusterActiveNode`.

**Recommendation**

Give `AkkaActiveNodeGate` an `ActiveNodeHealthCheckOptions` constructor, or factor the "resolve role,
then `SelfIsActive`" step into one shared `ClusterActiveNode` method that both the probe and the gate
call, so they share one scope definition. Until then, qualify the remarks: the guarantee holds only when
both are configured with the same single role or both unscoped.

**Resolution**

Resolved 2026-11-09 in the commit tagged `(scadaproj#48)` (Health `0.3.1`, unpublished) — added `AkkaActiveNodeGate.ForOptions(sp, ActiveNodeHealthCheckOptions)` and a shared `ClusterActiveNode.SelfIsActiveForPreference(cluster, rolePreference)` (resolve the first preferred role the node carries, then `SelfIsActive`; a node with none of the roles is never active), so the gate and `/health/active` share one scope definition. Chose a static factory over a second public constructor so an existing `new AkkaActiveNodeGate(sp, null)` call is not made ambiguous. Class remarks qualified. Tests `Gate_ForOptions_AgreesWithTheProbeOnEveryNode_ForAMultiRolePreference` and `..._NodeCarryingNoPreferredRole_IsNeverActive_AndEmptyPreferenceIsUnscoped` (new API, so they cannot compile without the fix).