Joseph Doherty
3a31dd2de7
SitePskProvider cached each site's gRPC preshared key forever; only site removal
invalidated it, so rotating SB-GRPC-PSK-{site} broke the central<->site link on
both central nodes until they restarted. The cached key is now dropped when:
- the secret is written through /admin/secrets: central replaces the secrets
library's ISecretCacheInvalidator with SitePskRotationInvalidator, which also
publishes SitePskInvalidated on a new DistributedPubSub topic
(site-psk-invalidation) so the peer central node drops its copy and its
resolver cache entry too (SitePskInvalidationSubscriber);
- a site rejects a central->site call with PermissionDenied/Unauthenticated:
WithSiteCredentials wraps every per-site channel's handler in
PskRejectionRefreshHandler, so the next call re-reads the key (covers
out-of-process writes such as the secret CLI);
- a site->central call presents a token that does not match the cached key:
CentralControlAuthInterceptor invalidates and re-reads once before refusing;
- ScadaBridge:Communication:SitePsks reloads.
Invalidation is case-insensitive because SecretName lowercases names. Rotation
runbook (topology-guide), Component-Communication/Host and the #85 cache audit
(D2) updated.
Claude-Session: https://claude.ai/code/session_01GT67AEHd2Acv1YPwGfXEoV
78 lines
7.5 KiB
Markdown
78 lines
7.5 KiB
Markdown
# Central per-node cache staleness audit (Gitea #85)
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**Date:** 2026-11-09. **Scope:** every in-process cache on a **central** node that holds
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configuration-database (or secret-store) state, and how stale it can be on the **peer** central
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node after a change is made through the other one. Same defect class as #83
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(`ExternalDefinitionLookupCache`).
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## Context that sets the risk
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- Traefik routes UI, `/management` and `/api/*` to the **active** central node only
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(`/health/active`). An edit and a use on different nodes therefore only happen when someone
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talks to a node directly (CLI pointed at a node's own port) or across a **failover**.
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- Every TTL below is measured from when the entry was loaded, so an entry a node cached while it
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was previously active is still bounded by its TTL after it becomes active again.
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- No cache below replicates its invalidation to the peer. Central already has one cross-node
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channel: the `DistributedPubSub` topic `CentralCommunicationActor.HealthReportTopic` (peer
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health replication). A config-invalidation broadcast, if an owner wants one, should be a second
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topic on the same mediator, published from `AfterConfigurationCommit`.
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## Inventory
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| Cache | Holds | Local invalidation | Peer staleness bound | Verdict |
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|---|---|---|---|---|
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| `InboundScriptExecutor` compiled handlers (InboundAPI) | Compiled method delegates | `InvalidateMethod` on delete; change bus on import | **None** — every request revision-checks the cached handler against the resolved `ApiMethod.Script` and recompiles on mismatch | OK |
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| `ApiMethodCache` (InboundAPI) | `ApiMethod` rows, incl. not-found | Change bus (bundle import); **management create/update/delete — added by #85** | `InboundApi:ApiMethodCacheTtl`, default **5 s** | OK (local gap fixed, see below) |
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| `ExternalDefinitionLookupCache` (ESG, central only) | External systems / methods / DB connections (found only) | 9 ManagementActor handlers (#65); bundle import (#83) | `ExternalSystemGateway:DefinitionCacheTtl`, **10 s** on central | Owner decision — #83 |
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| `RoleMappingCache` (Security) — the cache at `ManagementActor` `InvalidateRoleMappingCacheAfterCommit` | LDAP group → role map + Deployer site scopes | Mapping / scope-rule commands, post-commit | `Security:RoleMappingCacheSeconds`, default **30 s** (`0` disables) | Owner decision — see D1 |
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| `PendingUpdatesCache` (DeploymentManager, #91) | Fleet pending-updates snapshot | Deployment finished on this node | `DeploymentManager:PendingUpdatesCacheTtl`, default **60 s** | OK — display only |
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| `CentralCommunicationActor` site-address cache (+ `GrpcSiteTransport` channel pairs) | Site gRPC endpoints | Site create/update/delete → `RefreshSiteAddresses` | Periodic DB reload, **60 s** (hard-coded) | OK — rare edit, self-heals |
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| `SiteStreamGrpcClientFactory` clients | Per (site, endpoint) stream clients | Site delete → `RemoveSiteAsync` (local only) | Not stale data: a removed site's client on the peer is reclaimed by idle eviction, `Communication:GrpcClientIdleTtl` (**30 min**) × 1.5 after last use | OK — resource, not correctness |
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| `SitePskProvider` (Host) | Per-site gRPC PSK from config / secret store | Site removal; `SB-GRPC-PSK-{site}` write via `/admin/secrets`; site auth rejection; `SitePsks` reload (#96) | Write via `/admin/secrets`: **none** (peer told over `DistributedPubSub` topic `site-psk-invalidation`); other writes: first rejected call after `Secrets:ResolveCacheTtl` | Fixed — #96 (see D2) |
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| `DefaultSecretResolver` (shared `ZB.MOM.WW.Secrets`) | Decrypted secret values | Lib's own invalidator (UI writes, sync service) | `Secrets:ResolveCacheTtl`, **30 s** | OK — owned by the shared lib |
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| `KpiSnapshotCache` (CentralUI) | KPI query results (operational data) | — | **8 s** | OK — not config |
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| `SharedAlarmSummaryService` (CentralUI) | Per-site alarm summary fan-out | — | **12 s** cold-cache window | OK — not config |
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| `IDeploymentStatusNotifier` (DeploymentManager) | Push of deployment status to UI circuits | In-process event | Peer UI never sees the push, but the UI is only served by the active node and the pages also poll | OK |
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| `ITemplateGraphWatermark` / `FlattenSession` | Template-chain memo keyed by in-process version | Repository bumps | Session lives for one deploy/validate operation; the watermark is process-local by design (peer starts from 0 → extra work, never stale work) | OK |
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| `ScriptCompileVerdictCache`, `TrustVerdictCache`, `AuditRegexCache`, `ScriptAnalysisService` `IMemoryCache`, `OAuth2TokenService` | Pure functions of their key (code hash + surface, pattern, credential hash) | — | Not applicable — a changed input is a different key | OK |
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| `ZB.MOM.WW.Auth.ApiKeys.SqlServer` (inbound API keys) | — | — | No in-process cache in the shared store (checked in the 0.3.0 source) — revocation is immediate on both nodes | OK |
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## Fixed in #85
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**`ApiMethodCache` was not invalidated by the management API even locally.** Only the compiled
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handler was dropped, so for up to the 5 s TTL on the node that made the change:
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- a just-**deleted** method stayed callable — the executor recompiled it from the cached row;
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- a just-**created** method answered 404 if a not-found had been cached.
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`ManagementActor` now drops the method's cache entry post-commit on create, update and delete
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(`InvalidateApiMethodCacheAfterCommit`), the same post-commit pattern as the role-mapping cache.
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The peer is still bounded by the 5 s TTL. Tests: `ApiMethodCacheInvalidationTests` (3 of 4 fail
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without the fix; the fourth is the negative control).
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No peer-staleness case was **clearly** a bug: every config cache with peer staleness is
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TTL-bounded (5–60 s), its bound is documented at the cache, and the active-only routing means the
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window is only hit via a direct-to-node call or a failover inside the TTL. So no cross-node
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broadcast was added.
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## Needs an owner decision
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- **D1 — `RoleMappingCache` revocation lag on the peer (30 s).** Removing a mapping or narrowing a
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Deployer's site scope takes effect at once on the node that made the change and within 30 s on
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the other. It is a security-relevant window (revoked access keeps working briefly), but only on
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the node the change did *not* go through. Options: accept and document (current state); lower
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`RoleMappingCacheSeconds`; or add the `DistributedPubSub` invalidation topic described above.
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Recommendation: accept unless the operators' revocation SLA is tighter than 30 s.
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- **D2 — `SitePskProvider` caches a successful PSK resolve forever.** Its own remarks say
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`Invalidate` covers "a key rotated in place", but nothing calls it on rotation — only on site
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removal. Rotating `SB-GRPC-PSK-{site}` in the secret store (with the site pair restarted on the
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new key) leaves **both** central nodes dialling with the old key until they restart. Options: make
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central restart part of the rotation runbook; give the cache a TTL; or invalidate on a
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`PermissionDenied` from the site. Not peer-specific, so it is out of #85's fix scope — file it
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separately. **Resolved by #96:** all three — invalidate on the rotation write (and the peer, via
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the new `site-psk-invalidation` topic; the first config-invalidation broadcast topic D1/D3 could
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join), refresh on a site's auth rejection, and drop the cache on a `SitePsks` reload.
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- **D3 — `ExternalDefinitionLookupCache` peer bound (10 s).** Already tracked by #83; the
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recommendation there (accept and document) still stands. If D1 gets a broadcast topic, this cache
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and `ApiMethodCache` should join it rather than add a second mechanism.
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