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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

oto_thread_gap_recovered_total
Type counter
Labels reason — dead_delivery, skipped_delivery, missing_delivery, thread_dead
Registered in internal/platform/jobs/ordering/gate.go
Alertable yes. The help string says: sustained non-zero means a channel is broken
Rule OtoThreadGapRecovered in deploy/prometheus/oto-rules.yaml

What it counts

Section titled “What it counts”

Thread sequence slots the ordering gate advanced past, without being sent.

A channel thread hands out strictly increasing thread_seq values and the head only moves forward, so one slot that can never be filled would stall every message behind it forever. Rather than stall, the gate advances the head and records a delivery.skipped event — oto’s silence must never be indistinguishable from “no alert” (SPEC §H.9), so the skip is visible per alert in the UI.

already_sent is deliberately excluded. A head catching up with a message that did land is convergence, not breakage; counting it would make “sustained non-zero means a channel is broken” untrue.

What each reason means

Section titled “What each reason means”
reason What happened Was a message lost?
dead_delivery the delivery hit a terminal provider error yes — that update never reached the channel
skipped_delivery a coalesced no-op update no — nothing needed sending
missing_delivery the seq was allocated but no delivery row exists: the allocating transaction rolled back after next_seq++ yes — the slot can never be filled
thread_dead the thread itself is terminal; nothing more will ever send yes, for everything queued behind it

So a rate dominated by skipped_delivery is benign. Any sustained rate of the other three means people are not being told things oto decided to tell them.

What to check

Section titled “What to check”
  1. Split by reason first — the table above is the whole triage.
  2. notification_deliveries for that thread: status, error_class, attempts. A run of dead rows points at the channel.
  3. The channel’s health and UI banner — config_invalid and auth_expired are the two classes that set it, and they are the usual cause of dead_delivery en masse.
  4. oto_jobs_dead_total for kind="deliver.dispatch": the same failures seen from the job runtime.
  5. channel_threads for the thread: last_sent_seq versus next_seq, and whether the thread is marked dead. (frozen was a fourth state and is gone — git-bug e5c060b; nothing ever wrote it, so a query for it always returned nothing.)
  6. For missing_delivery: look for an error around the allocating transaction. A rollback after next_seq++ is a bug in the write path, not an operational condition.

What to do

Section titled “What to do”
  • dead_delivery / thread_dead: fix the channel (re-authorise, re-invite the bot, correct the configuration), then confirm new deliveries land. Past messages are not resent — the timeline in oto is the record; the delivery.skipped events show precisely what the channel missed.
  • missing_delivery: file it. It means a transaction allocated a sequence number and then rolled back, which no configuration causes.
  • skipped_delivery only: no action. Consider excluding it from your alert expression if it dominates your rate.