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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
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0009 — Rule definitions are snapshotted and versioned at fire time

Status: Accepted · 2026-08-07

Context

Section titled “Context”

“We fetch the rule from Prometheus” is a 40-line HTTP client, not a moat. GET /api/v1/rules returns expr, for, labels and annotations; Grafana already renders the rule query next to the alert. As a differentiator it survives about a Tuesday.

What nobody ships is provenance over time: “this alert fired — show me the rule expression as it was at that moment, and how the threshold has moved since.” Grafana shows the current rule. Fetching the rule and versioning it upgrades a trivial HTTP client into a real capability, and it directly serves the alert-hygiene wedge.

Matching an alert instance back to its rule is genuinely ambiguous: alertname is not unique across rule groups or files; alert_relabel_configs can rewrite it; rule labels: may contain {{ $labels.x }} templates so a naive subset check fails; external_labels are added on the way out so subset checks must be one-directional; and in a sharded setup the wrong Prometheus returns nothing.

Decision

Section titled “Decision”

Rule definitions are content-addressed and captured at fire time, then bound to the occurrence.

rule_fingerprint = sha256(expr || for || keep_firing_for || canon(labels) || canon(annotations))
rule_key         = (source_id, rule_file, rule_group, rule_name)

rule_snapshots is UNIQUE on (org_id, source_id, rule_fingerprint). alert_occurrences.rule_snapshot_id is the binding. Drift is “the snapshot bound to this occurrence has a different rule_fingerprint than the one bound to the previous occurrence for the same rule_key” → emit rule.definition_changed with a structured diff, and deliver a rule_changed Slack thread reply regardless of channel verbosity.

Two acquisition paths, in order:

  1. Primary — parse generatorURL. Its g0.expr is URL-encoded PromQL as evaluated. Zero API calls, zero ambiguity, and it works in multi-Prometheus setups. origin='generator_url'.
  2. Enrichment — GET /api/v1/rules?type=alert&rule_name[]=<alertname>&exclude_alerts=true on the Prometheus identified by generatorURL’s scheme+host, for for:, keep_firing_for: and the raw rule labels/annotations. origin='prometheus_api'. Cached aggressively.

Ambiguity (N>1 candidates) is scored on non-templated label subset plus annotation-key overlap and recorded as match_confidence ∈ {exact, probable, ambiguous, none}. ambiguous is surfaced in the UI and in Slack. It is never silently guessed.

duration and keepFiringFor are float seconds on the wire (600 means for: 10m).

Consequences

Section titled “Consequences”
  • oto answers “this alert fired because someone lowered the threshold from 90 % to 70 % two hours ago” — a support ticket resolved before it is opened. This is the strongest specific feature in the product.
  • The alert timeline gains a genuinely new event type that no competitor emits.
  • Snapshots are content-addressed, so a rule that never changes stores exactly one row across thousands of occurrences.
  • Requires network reachability to Prometheus (optional per source). Without it, origin falls back to generator_url (expr only) or unavailable — degraded honestly, never faked.
  • oto is strictly read-only against Prometheus rules and will never become a rule editor.

Alternatives rejected

Section titled “Alternatives rejected”
  • Fetch the current rule on demand at render time: shows today’s rule next to yesterday’s alert. That is the bug this ADR exists to prevent.
  • Match on alertname alone: wrong whenever two files define the same alert name, and silently so.
  • Store the whole /api/v1/rules response per occurrence: enormous duplication and no diffing primitive.