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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

0015 — No stream processor; River in Postgres is the pipeline

Status: Accepted · 2026-08-08 Relates to: 0001 (River and the transactional outbox), 0014 (one datastore)

Context

Section titled “Context”

oto’s shape — ingest a webhook, transform it, fan out to sinks with retries and backpressure — is almost exactly the shape Benthos / Redpanda Connect was built for. The question deserves a real answer rather than a reflex, because on the surface it is a good match: durable buffering, batching, retry policy, and Bloblang for mapping, all configuration rather than code.

Decision

Section titled “Decision”

We do not run a stream processor. The pipeline is River jobs over Postgres, with the ordering and suppression logic in Go.

The decisive argument is not “extra dependency” — it is that adopting Benthos would remove a correctness guarantee we currently hold. River enqueues a job in the same transaction as the state change that justifies it, which is what gives us the outbox property from 0001: either the occurrence opened and the notification job exists, or neither happened. Benthos’s at-least-once delivery is not transactional with our Postgres writes. We would be trading an invariant for a pipe.

The supporting arguments:

  • Every hard part of this system is stateful in Postgres — the occurrence state machine, dedup by identity key, per-thread sequence gating on advisory locks, and the suppressor precedence chain. None of it is expressible in Benthos. It would end up a thin pipe with all the logic still in Go.
  • The one-helm install-plus-Postgres deployment story is a product asset, not just an operational convenience.
  • A second configuration language (Bloblang) becomes a second place where routing behaviour is defined, and therefore a second place it can be wrong, in a system where being wrong means a missed page.

What we keep from the idea. Benthos is Go, and Bloblang is importable as a library. When we want user-authored input mapping — “map this vendor’s webhook into oto’s alert model” without a recompile — embedding Bloblang (or CEL, per 0017) gives us that with no second runtime. That is the sanctioned path if the need arrives.

Consequences

Section titled “Consequences”
  • Throughput is bounded by Postgres and by River’s worker pool rather than by a purpose-built stream engine. This is acceptable at the volumes established in 0014.
  • Retry, backoff, dead-lettering and backpressure are ours to own and to test. They are already implemented in internal/platform/jobs, including the per-thread ordering primitive that no off-the-shelf processor provides.
  • Adding a new input source means writing Go, not editing a config file. Accepted for v1; the Bloblang-as-library path exists if the source count grows.

Alternatives rejected

Section titled “Alternatives rejected”

Benthos / Redpanda Connect as a service. Rejected above. The transactional-enqueue loss is the disqualifier; the second runtime and second config language are the aggravating factors.

Kafka partitioned by thread key. Would make per-thread ordering correct by construction rather than by advisory lock — a genuine improvement to the subtlest code in the system. Rejected because it adds a broker to a product whose only dependency is Postgres, and imposes a partition ceiling on thread concurrency. Reconsider only if the ordering primitive proves unreliable in practice.

Temporal or a durable-execution engine. A better conceptual fit for the multi-step notification lifecycle than a stream processor is. Rejected for the same dependency reason, and because River’s transactional insert already covers the specific guarantee we care about.