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Design
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
oto runbooksAlert search — optional partial/substring matching on alert namesoto_clock_skew_secondsoto_delivery_claim_lost_totaloto_ingest_accepted_totaloto_ingest_alerts_totaloto_ingest_duplicate_totaloto_ingest_duration_secondsoto_ingest_fingerprint_mismatch_totaloto_ingest_process_duration_secondsoto_ingest_rejected_totaloto_ingest_shed_totaloto_job_duration_secondsoto_job_queue_depthoto_jobs_dead_totaloto_jobs_enqueued_totaloto_jobs_failed_totaloto_jobs_panics_totaloto_jobs_snoozed_totaloto_jobs_started_totaloto_jobs_succeeded_totaloto_jobs_unknown_version_totaloto_render_invalid_totaloto_slack_unknown_action_totaloto_stream_connectionsoto_stream_events_coalesced_totaloto_stream_events_dropped_totaloto_stream_events_fetched_totaloto_stream_events_published_totaloto_stream_fetch_errors_totaloto_stream_listener_reconnects_totaloto_stream_notify_malformed_totaloto_stream_notify_received_totaloto_stream_poll_recovered_totaloto_stream_resync_totaloto_thread_gap_recovered_totaloto_thread_head_wait_secondsoto_thread_order_decisions_total

0001 — PostgreSQL is the sole datastore; River is the job queue

Status: Accepted · 2026-08-07

Context

Section titled “Context”

oto needs a system of record, an append-heavy event log, a job queue, a rate limiter and a pub/sub bus. The obvious instinct is Redis for the queue, ClickHouse or Loki for events, and Postgres for entities. The entire go-to-market for a self-hosted alerting tool is the install experience: helm install plus one database. Every additional dependency is an operational tax paid by the buyer, and it is exactly the footprint advantage oto has over Keep.

The decisive technical point is the dual-write problem. With an external broker, the state change commits and the enqueue can fail (notification lost), or the enqueue succeeds and the commit rolls back (duplicate notification). Both are unacceptable in a product whose premise is “never lies”.

Decision

Section titled “Decision”

Postgres only. No Redis, no Kafka/NATS, no ClickHouse/Loki/Elasticsearch, no TimescaleDB. The job queue is River — pgx-native, SELECT … FOR UPDATE SKIP LOCKED, with river.InsertTx(ctx, tx, args) placing the job in the same transaction as the domain write. That is a transactional outbox with none of the outbox boilerplate.

Volume is handled with native declarative partitioning: alert_events monthly, ingest_batches daily, ui_events hourly. Retention is DETACH + DROP, never DELETE.

Consequences

Section titled “Consequences”
  • Exactly one backup story, one connection-pool story, one failure mode.
  • Enqueue is exactly-once with respect to the domain write. This is worth more than any throughput an external broker would add — the ceiling here is Slack’s 1 msg/s/channel, not the queue’s.
  • Long transactions holding a job open would wreck autovacuum, so the delivery worker MUST claim-then-work-then-ack with short transactions and MUST NOT hold a transaction across the Slack call.
  • Completed-job retention and queue bounds are mandatory, not optional.
  • Revisit only above roughly low-thousands of jobs/sec. db.Enqueuer is an interface so the swap is possible.

Alternatives rejected

Section titled “Alternatives rejected”
  • asynq (Redis): faster, but no transactional enqueue, and a second datastore in a one-install product.
  • Kafka/NATS: correct at 100× the volume; an operational tax paid for nothing at ours.
  • TimescaleDB: genuinely attractive (hypertables, compression) but it is still an extension to install, version and support. Native partitioning is sufficient at 50M events/month.
  • ClickHouse for the event stream: doubles the operational surface and breaks the one-install promise, which is a competitive advantage worth protecting.