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oto — System Design ProposalDomain Research: Prometheus Alertmanager + Slackoto — Red-Team Memooto — SCOPE BOUNDARY (the doctrine)oto — BINDING SPECIFICATION v1
ADRs
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`
Runbooks
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0003 — Alert, AlertOccurrence and AlertEvent are three distinct entities

Status: Accepted · 2026-08-07

Context

Section titled “Context”

“Alert” is overloaded to uselessness: Prometheus calls a rule an alert, Alertmanager calls a label set an alert, humans call a Slack message an alert. The brief treated occurrence and event as one concept. The product promise — a Sentry-style, replayable lifecycle timeline — cannot be built on a mutable row.

Decision

Section titled “Decision”

Three entities:

  • Alert — the identity of a label set within (org, cluster). Created on first sight, survives resolution forever. Millions of rows, bounded by label cardinality, not by time.
  • AlertOccurrence — one contiguous firing episode, (alert_id, seq). A stateful interval with a start and an end. It is what you ack, and whose firing duration is measured. (The acronym “MTTR” is banned as of ADR 0013; use “firing duration”.)
  • AlertEvent — an immutable record of one thing that happened at one instant. Append-only. Never updated, never deleted; aged out by DROP PARTITION.

Rule of thumb for engineers: if you would ever want to UPDATE it, it is not an Event.

Every AlertEvent carries two timestamps: occurred_at (the upstream’s claim) and recorded_at (oto’s clock). Timelines ORDER BY (recorded_at, id) and display occurred_at. Ordering by a remote clock is how you get a “resolved” event above a “firing” event.

Consequences

Section titled “Consequences”
  • The timeline is an honest audit trail, because rendering it never mutates it.
  • Current state is a cheap, narrow, heavily-indexed projection (alerts), so the hot list query never touches the event log.
  • “This has fired 47 times this quarter” survives, because a re-fire is a new occurrence on the same Alert, never a new Alert.
  • Costs one extra join for detail views and one extra table to keep consistent. The occurrence projection onto alerts is written in the same transaction as the transition.
  • Clock skew becomes measurable and is surfaced as a feature (oto_clock_skew_seconds), because skew is a real problem in the customer’s cluster.

Alternatives rejected

Section titled “Alternatives rejected”
  • Collapse occurrence into event: forces either mutating timeline rows (destroying the audit trail) or having no natural key for “the thing this Slack thread is about”.
  • Collapse alert into occurrence: destroys the history that is the product.
  • One timestamp per event: the headline feature would visibly lie whenever a cluster’s clock drifts.