Joseph Doherty
f9f1b8fcee
Gate record: docs/plans/2026-07-20-localdb-phase2-live-gate.md. Checks 1, 2, 5, 6 pass. Checks 3 and 4 are NOT satisfied — the defect they were meant to confirm turned out to be the opposite of what the plan assumed. Three defects crash-looped every driver node before check 1 could even run: 1. An empty ServerHistorian:ApiKey kills the host. ServerHistorianOptions- Validator exists to turn exactly that class of failure into a named OptionsValidationException, but its documented fail tier explicitly excluded ApiKey on the reasoning that a keyless client "degrades — the gateway rejects calls". It does not: the client validates its own options at construction, so the process dies during Akka startup and never makes a call. 2. UseTls disagreeing with the endpoint scheme kills the host too, in both directions (both messages confirmed in the shipped client assembly). Moving an endpoint from https to http without clearing UseTls is an ordinary migration slip. 3. Plaintext h2c was UNREACHABLE. HistorianGatewayClientAdapter forwarded the TLS-only options unconditionally, and AllowUntrustedServerCertificate defaults to false, so it always sent RequireCertificateValidation=true — which the client rejects outright when UseTls=false. Every http:// deployment crashed, though the scheme is documented as the supported way to select h2c, and the only workaround was to assert a certificate posture for a connection that has no certificate. The fourth was the blocker, and it is Phase 2's own: 4. The drain gate deferred to a Primary that cannot deliver. Redundancy roles are elected CLUSTER-WIDE; the alarm queue is PAIR-LOCAL. On the rig the elected driver Primary is central-1 — it carries the driver Akka role, replicates nobody's LocalDb and does not even run the alarm historian — so every driver node logged "Historian drain suspended", including the two site-b nodes that have no peer at all. Nothing drained anywhere, where before Phase 2 it drained fine. The cost is not a duplicate; it is the buffer growing to the capacity wall and evicting the audit trail it exists to protect. Fixed in three layers: a separate ShouldDrainAlarmHistory policy (unknown role drains; the two gates now deliberately disagree, and a test pins that); peer- host matching in DriverHostActor so a node stands down only for a Primary holding its rows; and AddAlarmHistorian short-circuiting the gate when replication is unconfigured — testing BOTH Replication:PeerAddress and SyncListenPort, since only the dialing half sets the former while both halves share the queue. Every one of these follows from the asymmetry: a false allow costs a duplicate row, which at-least-once delivery already accepts and payload-hash ids collapse; a false deny loses data silently. A third vacuous test, caught by the same delete-the-guard discipline: the role-view tests stayed green with the guard removed, because AwaitAssert polls until an assertion passes and the assertion was "reads open" — which is the SEEDED value, satisfied at the first poll before the actor processed anything. They now assert the sequence of published values through a recording view; the control then goes red for exactly the cases that matter. Migration evidence: 11 legacy rows across two deliberately overlapping files converged to exactly 9 identical rows on both nodes, proving D-6's payload-hash identity on real nodes rather than in a fixture. Open design fork, recorded in the gate doc rather than decided here: a pair cannot currently identify its own Primary, so both halves drain. Safe in every topology — nothing loses data — but the gate's de-duplication benefit is unrealised until roles are scoped per pair. Claude-Session: https://claude.ai/code/session_01GASWkNEi68FSCtvr6rLoEW
11 KiB
LocalDb Phase 2 — live gate (docker-dev rig)
Task 8 of
2026-07-20-localdb-adoption-phase2.md. Evidence log. Rig: localdocker-dev/docker-compose.yml— 2 central + site-a pair (replication ON) + site-b pair (default-OFF), one Akka cluster, one shared SQL.Safety rules followed (same as the Phase 1 gate): all DB inspection via
docker cpof thedb/-wal/-shmtriplet out of the container, querying the copy — never hostsqlite3on the live WAL file.
Headline
The gate did not get past its own first boot before finding real defects. Four production bugs, all fixed on-branch with regression tests, plus a fifth finding in the test suite itself. Three of the four crash-looped every driver node; the fourth silently stopped alarm history everywhere.
Checks 1, 2, 5 and 6 pass. Checks 3 and 4 are NOT satisfied — see "The blocker" below; they cannot be run as written on a rig that has no per-pair redundancy roles, and the defect they were meant to confirm turned out to be the opposite of what the plan assumed.
Seeding the migration
The rig had no pre-consolidation alarm-historian.db, so one was synthesised per node and docker cp-ed to /app/alarm-historian.db (the WORKDIR-relative default) into created-but-not-started
containers — the exact upgrade shape.
Deliberately overlapping content, to test D-6 in production: 6 rows on site-a-1, 5 on site-a-2,
2 of them byte-identical payloads (the warm-pair duplication HistorianAdapterActor produces in
every boot window). 11 legacy rows, 9 distinct.
Defects found and fixed
1. Empty ServerHistorian:ApiKey crash-loops the host (was classified "degrades")
AlarmHistorian:Enabled=true requires the gateway alarm writer, which requires a key.
HistorianGatewayClientOptions.Validate() throws The gateway API key must not be empty inside the
client factory during Akka startup, so every driver node crash-looped.
ServerHistorianOptionsValidator exists precisely to convert that class of failure into a named
OptionsValidationException — but its documented fail tier explicitly excluded ApiKey, reasoning
that a keyless client "degrades rather than crashes (the gateway rejects calls)". That premise is
false: the client validates its own options at construction, so the process dies before any call.
Fixed; the key is never echoed in the message.
2. UseTls / endpoint-scheme mismatch crash-loops the host
Immediately after fixing #1, the rig crash-looped again: UseTls defaults to true, the rig
endpoint is http://, and the client throws UseTls requires an https gateway endpoint. The
inverse (https:// + UseTls=false) throws too — both strings confirmed in the shipped client
assembly. Setting an http endpoint without clearing UseTls is an ordinary migration slip that
takes the host down. Now validated in both directions.
3. Plaintext h2c was unreachable — every http:// deployment crashed
Third crash-loop, and a genuine product bug rather than operator config.
HistorianGatewayClientAdapter.Create forwarded the TLS-only options unconditionally, and
AllowUntrustedServerCertificate defaults to false, so it always sent
RequireCertificateValidation=true — which the client rejects outright when UseTls=false
(RequireCertificateValidation is a TLS-only option and requires UseTls=true).
CLAUDE.md and docs/Historian.md both document http:// as the supported way to select h2c, but
no h2c configuration could start, and the only workaround was to claim
AllowUntrustedServerCertificate=true — a certificate posture for a connection with no certificate.
Fixed: TLS-only options stay at their defaults when UseTls=false.
4. THE BLOCKER — the drain gate deferred to a Primary that cannot deliver
With the rig finally up, every driver node logged Historian drain suspended. Nothing drained
anywhere — including the two site-b nodes, which have no redundancy peer and no replication at all.
Before Phase 2 this deployment drained fine, because the drain was ungated.
Root cause, established from the rig rather than guessed:
RedundancyStateActorderives roles from Akka's cluster-wideRoleLeader("driver").central-1/central-2carry bothadminanddriverAkka roles (OTOPCUA_ROLES=admin,driver).- So the elected driver Primary is central-1 — a node that replicates nobody's LocalDb and does not even run the alarm historian.
- Every site node was
Secondary, saw that a Primary existed, and stood down in its favour.
The redundancy role is a cluster-wide election; the alarm queue is pair-local. Deferring on "somebody is Primary" is therefore wrong in principle: in a multi-pair fleet the Primary is usually in another pair and holds none of this node's rows. The consequence is not a duplicate — it is the buffer growing on every node until the capacity wall evicts the oldest events, i.e. silent permanent loss of the audit trail the queue exists to protect.
Fixed in three layers, each with a positive control:
PrimaryGatePolicy.ShouldDrainAlarmHistory(role, queueSharingPeerIsPrimary)— a separate policy fromShouldServiceAsPrimary. Unknown role ⇒ drain. A node stands down only for a Primary that holds its rows. The two gates now deliberately disagree, and a test pins that disagreement so nobody "harmonises" them back.DriverHostActorpublishes that verdict, matching the snapshot's Primary against this node's configured LocalDb replication peer host.AddAlarmHistorianshort-circuits the gate entirely when replication is not configured — a node whose rows exist nowhere else must never defer. The predicate tests bothReplication:PeerAddressandSyncListenPort, because only the dialing half sets the former and both halves share the queue.
The asymmetry of the error costs is what drives every one of these: a false allow costs a duplicate history row, which the design already accepts (at-least-once across a failover, by design, and payload-hash ids collapse identical events); a false deny loses data silently.
5. A third vacuous test — AwaitAssert on the seeded value
Deleting the guard (publishing the old write-gate verdict) left DriverHostActorRoleViewTests
green. AwaitAssert polls until an assertion passes, and the assertion was "the view reads
open" — which is also the value the view is seeded with, so it succeeded at the first poll, before
the actor had processed anything. It could not distinguish a correct publish from no publish at all.
Fixed by asserting on the sequence of published values via a recording view, never on current state. Re-run under the control: red, for exactly the cases that matter. This is the same "absence-assertion passes by race" trap recorded for #485/#486, in a new disguise.
Checks
| # | Check | Result | Evidence |
|---|---|---|---|
| 1 | Migration ran; .migrated sidecar on both site-a nodes; row counts match |
✅ PASS | alarm-historian.db.migrated present on both. 11 legacy rows across the two files → exactly 9 rows on each node, id sets byte-identical — the 2 shared payloads collapsed, proving D-6's payload-hash identity in production. Each node holds the other's rows (legacy/a1-only-* present on a-2 and vice versa). Legacy attempt_count distinction survived the copy (the 3-attempt row still leads the 0-attempt rows), last_error carried, 0 dead-lettered |
| 2 | Alarm burst converges: identical rowsets, oplog drains to 0, dead letters 0 | ✅ PASS | Identical id sets on both nodes; __localdb_oplog depth 0 on both; 0 dead-lettered. Drain visibly live against the deliberately unresolvable gateway — attempt_count climbing 33 → 42 → 168 with last_error='retry-please', which is exactly the buffering behaviour the queue exists for |
| 3 | Only the primary drains | ❌ NOT SATISFIED — see defect 4 | As written the check assumes a per-pair Primary exists. On this rig the elected Primary is a central node outside both pairs, so the honest post-fix behaviour is that all four nodes drain. No node can currently identify a queue-sharing Primary: site-b is unpaired, and of the site-a pair only the dialing half knows its peer. Safe (no loss, duplicates only), but the check's intent is unproven |
| 4 | Failover: standby resumes draining; count double-delivered events | ⛔ NOT RUN | Superseded by defect 4. A meaningful failover test needs a rig where the pair itself elects a Primary; measuring "double delivery" is meaningless while both halves drain unconditionally |
| 5 | Both nodes restarted together: clean rejoin, identical counts, no I/O errors | ✅ PASS | docker compose restart site-a-1 site-a-2 → 0 disk I/O error / SQLITE_IOERR / corrupt lines and 0 fatals in either log; both back to 9 rows / 0 dead / oplog 0, still identical |
| 6 | site-b default-OFF pin: sink works locally, no sync traffic | ✅ PASS | alarm_sf_events created and registered on both site-b nodes; port 9001 not bound (/proc/net/tcp), no sync listener, no replication config; both drain their own queue (defect 4's third fix) with 0 fatals |
The open design question
The gate leaves one question that is a design fork, not a bug to patch:
A pair cannot currently identify its own Primary. Redundancy roles are elected cluster-wide, but
the queue is pair-local. Only the dialing half of a pair knows its peer (Replication:PeerAddress);
the listening half sets SyncListenPort only. So the drain gate can never fully engage, and both
halves of a replicated pair drain — safe, but duplicated.
Three ways out, in increasing order of scope:
- (A) Configure both halves to dial. Smallest change; makes the peer known on both sides so the gate engages symmetrically. Needs confirmation that the LocalDb library accepts bidirectional dial, and an operator-facing config change.
- (B) Accept duplicates for unpaired-role deployments. Change nothing further, document that the gate only engages when redundancy roles are configured per pair. Cheapest; leaves the steady-state double-delivery the gate was introduced to remove.
- (C) Scope redundancy roles per pair in
RedundancyStateActor. Fixes the root cause for every consumer of the role (ServiceLevel, scripted-alarm emit gate, inbound-write gate), all of which inherit the same cluster-wide assumption. Largest blast radius, and the only one that makes "Primary" mean what the docs say it means in a multi-pair fleet.
The branch is safe in every topology as it stands — no configuration loses data — so this is a question of when to reclaim the de-duplication benefit, not an outstanding hazard.
Not merged
Per the plan, nothing on this branch is merged.