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oto — System Design ProposalDomain Research: Prometheus Alertmanager + Slackoto — Red-Team Memooto — SCOPE BOUNDARY (the doctrine)oto — BINDING SPECIFICATION v1
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0001 — PostgreSQL is the sole datastore; River is the job queue0002 — `internal/<domain>/{api,service,repository,domain}` with three model sets0003 — Alert, AlertOccurrence and AlertEvent are three distinct entities0004 — oto owns alert identity; Alertmanager's fingerprint is recomputed, not trusted0005 — A durable group key, and the AlertGroup generation owns the Slack thread0006 — The Alertmanager API v2 reconciler is mandatory, not optional0007 — Webhook response contract: 202 or 503. Never 4xx, never 429.0008 — Slack: `chat.update` in place is primary; threads are secondary; one colour attachment0009 — Rule definitions are snapshotted and versioned at fire time0010 — Server-Sent Events with durable resume, not WebSocket0011 — Validation is seven layers with two opposite trust models0012 — Pastel product chrome, saturated colour reserved exclusively for state0013 — oto is alert-first: the Flight Recorder Test defines the scope boundary0014 — Postgres is the only store; no TSDB or column store in v10015 — No stream processor; River in Postgres is the pipeline0016 — Cluster context arrives via MCP, on demand; never the Kubernetes event firehose0017 — Alertmanager-style matchers, not CEL; and a filter AST that keeps the door open0018 — Slack distribution: a customer-built internal app, credentials in config0019 — MIT licence0020 — Broadcast the transitions that must be seen0021 — Correctness and testing strategy0022 — Length-prefixed identity pre-images0023 — Terminal thread states are decided first, and the send is three phases0024 — Retention defaults, what each boundary destroys, and cold storage0025 — The alert list resolves rule snapshots in a batch, not per row0026 — `refire_grace` and the flap thresholds, derived from a real rule corpus0027 — Delivery drills: a synthetic alert through the real pipeline, and the mark that keeps it out of the numbers0028 — Non-urgency motion: one-shot events, honest activity loops, and nothing else0029 — Type and radius scales, read off the product rather than drawn for it0030 — Tier A repainted as Washi & Ink / Konshi Sutra; accent moves to beni0031 — Sharp corners and higher-contrast grid lines within Washi & Ink; colours unchanged0032 — Dark-theme accent moves from beni to plum-blossom blue-and-white; light untouched0033 — The alert filters are a toolbar above the table, not a panel in the rail0034 — Notifications is a destination, and the record it keeps is readable0035 — Decorative ink as a masked wash: one primitive, four motifs, and the placements it is refused0036 — AlertOccurrence becomes AlertCase, and `case` is argued against FR-1 by name0037 — A Wording is Liquid, and the structure around it stays oto's0038 — The group key is derived from the alert's own labels0039 — Group close stays activity-driven0040 — A Case is `open` or `closed`, and it is never reopened0041 — The Alert/Case allocation, and the one rule that decides it0042 — Storm damping is removed, because the defence was built before its object0043 — The Slack action row renders five elements, and the fifth is the snooze pair0044 — A count condition is a silence the operator asked for, and `below_threshold` is how oto says so0045 — A Case is a conversation, and one Slack thread per alert is the accepted cost0046 — Corners round again: ADR 0031's radius override is reversed0047 — A channel answers to a connection, and Slack gets two scopes back0048 — A Wording is spelled by its channel, and the marks in between are oto's0049 — A Wording is selected by its own clause, not by a route0050 — A NotificationTemplate is one whole message, and its policy says which one0051 — A `raw` template owns the whole message, and a template may carry its replies0052 — An Incident is drawn over Cases, and its response is handed off0053 — An Investigator reads, proposes, and never decides delivery0054 — A Remedy earns the write path0055 — An incident-tool integration is data or a bridge, never code inside oto0056 — A Case the upstream stopped speaking about expires, and says why
Setup
Configuration referenceReaching an incident tool: the envelope, a mapping, or a bridgeInvestigatorsRemediesConnecting oto to SlackThe live Slack verification runTuning otoConnecting oto to VictoriaMetrics (vmalert)The generic webhook and `oto.notification.v1`
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0004 — oto owns alert identity; Alertmanager's fingerprint is recomputed, not trusted

Status: Accepted · 2026-08-07

Context

Section titled “Context”

Alertmanager’s fingerprint is FNV-1a 64-bit over the sorted full label set, rendered as 16 hex chars. It is deterministic, present since AM 0.19.0, identical across HA peers, and fully reproducible locally by importing prometheus/common/model.

It also has no tenant in it, no cluster in it, and no way to say “prometheus_replica is not part of identity” without editing someone else’s Alertmanager config.

An earlier draft justified an oto-owned key by 64-bit birthday collisions. That justification is overstated and is not the reason.

Decision

Section titled “Decision”

Two keys, both stored, both indexed, with different jobs.

alert_key is the product identity and the dedup key:

"ak_" || base32hexLower(sha256(field(org_id) || field(cluster_key) || canon(labels, ignore))[0:16])

where field(x) := uint32be(len(x)) || x. The 0x00 separators this ADR originally specified were replaced pre-release by 0022: NUL termination is injective only if no field can contain a NUL, and receiver, expr and Alertmanager’s groupKey all can. 128 bits, scoped by (org, cluster_key), with a per-source ignore_labels deny-list applied before hashing. UNIQUE (org_id, alert_key) — dedup is enforced by the constraint, never by a read-then-write check, which races under concurrency.

source_fingerprint is Alertmanager’s fingerprint, recomputed locally over the full label set. If the wire value differs from ours, we store ours and emit ingest.fingerprint_mismatch. It is the join key for /api/v2/alerts reconciliation and for debugging against upstream. It is never the product identity.

Consequences

Section titled “Consequences”
  • Identical KubePodCrashLooping{namespace="prod",pod="api-0"} in prod-eu and prod-us are different Alerts — correct, because they are different problems with different blast radii.
  • HA Alertmanager replicas registered against the same Cluster collapse into one Alert, one occurrence, one Slack thread.
  • Cross-cluster correlation is never an implicit merge. It would be an explicit human act — and that capability is deferred post-v1.
  • oto is immune to the fingerprint field being absent, wrong, or produced by a Grafana webhook.
  • Changing ignore_labels creates new identities rather than re-keying. Documented; a re-key and merge job is deferred.

Alternatives rejected

Section titled “Alternatives rejected”
  • Use AM’s fingerprint as the primary key: dramatically simpler reconciliation, but no tenant/cluster scoping and no identity policy — permanently hostage to upstream label hygiene.
  • Trust the wire value without recomputing: free, and wrong the first time a proxy, a custom payload: template, or Grafana changes the shape.