Cron

Cron is declared in wrangler and implemented as scheduled on the Worker. celld runs the handler when a schedule is armed on that version’s fleet. cellp decides which ready versions arm triggers.crons at deploy time so preview fleets do not multiply production side effects.

Bindings overview · Binding guides

1. Declare it

"triggers": { "crons": ["0 * * * *"] }

2. Handle it

export default {
  async fetch(request, env) { /* HTTP */ },

  async scheduled(controller, env, ctx) {
    await env.CACHE.put('cron:last-run', String(controller.scheduledTime))
  },
}

Handlers

3. cellp scheduling policy

Cron does not branch data—there is no forked “cron state.” What changes per version is whether cellp passes triggers.crons into celld deploy for that version.

Project state	Version	scheduled runs?
No production yet (prod_version_id empty)	Any version that deploys ready	Yes — cellp arms crons on deploy for that version
Production set	Version id equals prod_version_id	Yes
Production set	Preview (any other ready version)	No — deploy uses a wrangler view without triggers.crons; artifact on disk is unchanged
Any	Archived or not ready	No — process stopped

Implications:

• While prod_version_id is empty, any version that deploys ready may arm crons; the first ready version normally becomes production and sets that pointer. If several ready versions exist before then, more than one fleet may arm the same expression—keep one ready line or cut over promptly if you need a single scheduler. After production exists, only the prod version arms.
• GET …/bindings still shows cron expressions from the artifact wrangler even when preview deploy stripped them for celld.
• After promote, cellp redeploys and restarts the old and new production versions (when still ready) so only the new prod fleet arms crons.

Dashboard lists expressions; there is no “run now” in cellp.

celld vs Cloudflare

• Rejects descending ranges (SAT-SUN, NOV-FEB) and * inside a list (1,*).
• After fleet downtime, celld runs the most recent missed occurrence once.
• One handler at a time per script; failures retry until the next tick unless the handler calls noRetry().
• A service-binding target cannot run its own Cron Triggers.

Full notes: celld cloudflare-compat — Cron Triggers.