Cron Jobs

import Arbiter.Worker.Cron qualified as Cron

let Right healthCheck = Cron.cronJob
      "health-check"        -- unique name
      "*/5 * * * *"         -- every 5 minutes (UTC)
      Cron.SkipOverlap      -- skip tick if previous job is still pending/running
      (\_kind tick -> Arb.defaultJob (RunHealthCheck tick))

    -- with backfill: catch up on missed ticks after downtime or scheduler delays
    Right nightlyReport = Cron.cronJob
      "nightly-report"
      "0 3 * * *"           -- 03:00 UTC daily
      Cron.AllowOverlap $ \kind tick -> -- each tick produces its own job
        let jobPriority = case kind of
              Cron.Replay -> 10
              Cron.Live -> 0
         in Arb.defaultJob (GenerateReport tick) & Arb.setPriority jobPriority
    nightlyWithBackfill = nightlyReport {Cron.backfill = Cron.Backfill 86400}

    -- in a specific timezone (validated at construction)
    Right marketOpen = Cron.cronJobInTimezone
      "market-open"
      "America/New_York"    -- IANA tz name
      "30 9 * * 1-5"        -- 09:30 local, Mon-Fri (DST-aware)
      Cron.SkipOverlap
      (\_kind tick -> Arb.defaultJob (OpeningBell tick))

config <- Worker.transactionalWorkerConfig 4 processScheduled
let configWithCron =
      config {Worker.cronJobs = [healthCheck, nightlyWithBackfill, marketOpen]}

The builder receives a TickKind (Live for the current minute, Replay for a catch-up tick) and the tick time.

A schedule enqueues one job per tick on its pool's queue. Tree jobs spawn children at runtime.

Time zones. Expressions are UTC. cronJobInTimezone takes an IANA name. 30 2 * * * skips a spring transition day with no 02:30. 30 1 * * * runs once on a fall transition day with two 01:30s. A * minute or hour field (*/5 * * * *, 0 * * * *) runs through both 01:00 hours.

Backfill. Backfill n replays ticks missed in the last n seconds after downtime or a scheduler pause. If a tick fails to insert, the scheduler logs the failure and continues with later ticks. A failed tick is skipped once a later tick fires. For a Backfill schedule, a failed newest tick is retried on the next pass.

Runtime overrides. The REST API and admin UI set a schedule's expression, overlap policy, time zone, and enabled state. An override of null restores the value from code.

Schedule type: Arbiter.Worker.Cron Haddocks.