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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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0007 — Webhook response contract: 202 or 503. Never 4xx, never 429.

Status: Accepted · 2026-08-07

Context

Section titled “Context”

Alertmanager’s retry classifier is unambiguous:

if statusCode/100 == 2 { return false, nil }              // success
retry := statusCode/100 == 5 || slices.Contains(r.RetryCodes, statusCode)

The webhook integration sets no RetryCodes. Therefore:

  • 2xx = success, recorded in the nflog, body ignored.
  • 5xx = retried.
  • 4xx (including 429) = failure, not retried, permanently lost.

Retries are unbounded but bounded by the group’s context deadline: max(group_interval, 10s) + peer_position × cluster.peer-timeout — about 5 minutes with common defaults. notify.MinTimeout is 10 seconds, which is the hard floor on how long we may take.

The trap is obvious and common: an overloaded service returns 429 or 503-shaped 4xx, and the alert is silently deleted forever — during the exact window when the customer’s cluster is on fire.

Decision

Section titled “Decision”
Condition Status
Durably persisted (or a recognised duplicate) 202
Overloaded, pool exhausted, statement timeout, queue insert failed 503 + Retry-After: 5
Missing/invalid/revoked or wrongly-scoped ingest token 401
Body over 8 MiB 413 (recorded in ingest_rejections)
Undecodable body 400 (recorded in ingest_rejections)
Anything transient NEVER 4xx. NEVER 429.

The handler does exactly three things inside one short transaction on a dedicated ingest connection pool with a 500 ms acquisition timeout and a 2 s statement timeout: insert the dedup key, insert the raw batch, river.InsertTx the processing job. No outbound network call is permitted on this path. Target p99 < 250 ms; hard ceiling 5 s.

A 2xx is a promise. Never return 2xx for a payload we failed to persist.

Consequences

Section titled “Consequences”
  • Backpressure has a designed, correct channel: shed load deliberately with 503 and let Alertmanager’s own ~5-minute retry budget absorb it.
  • The ingest pool is sized separately from the read/UI pool, so a slow dashboard query can never starve ingestion.
  • Storms become a queue-depth problem rather than a data-loss problem.
  • We cannot signal anything back to Alertmanager on success — the body is ignored — so all operator feedback lives in oto’s own UI and metrics.

Alternatives rejected

Section titled “Alternatives rejected”
  • 429 for rate limiting: the single most tempting mistake here; it deletes the alert.
  • Process synchronously and only notify asynchronously: simpler to debug and gives read-your-writes, but couples webhook latency to write contention during storms and leaves no replay artefact.
  • An on-disk spool ahead of Postgres: genuinely valuable, but Alertmanager’s retry budget is a sufficient buffer for v1, and a local WAL is a second durability story to get right.