rwsdk Cron Triggers

Schedule recurring background tasks using standard cron syntax. Tasks run automatically in production. Use for cleanup, metrics, billing, backups, and maintenance.

Quick Setup

1. Configure wrangler.jsonc

{
  "triggers": {
    "crons": [
      "0 * * * *", // Every hour
      "0 21 * * *" // Daily at 9 PM UTC
    ]
  }
}

Run pnpm generate after changes.

2. Add Scheduled Handler

export default {
  fetch: app.fetch,
  async scheduled(controller: ScheduledController) {
    try {
      switch (controller.cron) {
        case '0 * * * *': {
          await cleanupExpiredSessions();
          console.log('✅ Hourly cleanup complete');
          break;
        }
        case '0 21 * * *': {
          await processBilling();
          console.log('✅ Daily billing complete');
          break;
        }
        default: {
          console.warn(`Unhandled cron: ${controller.cron}`);
        }
      }
    } catch (error) {
      console.error('Cron error:', error);
    }
  },
} satisfies ExportedHandler<Env>;

Each case must match a cron in wrangler.jsonc.

Cron Syntax

┌─ minute (0-59)
│ ┌─ hour (0-23)
│ │ ┌─ day (1-31)
│ │ │ ┌─ month (1-12)
│ │ │ │ ┌─ weekday (0-6, Sun-Sat)
* * * * *

Common patterns:

• * - Every minute (testing only)
• /5 * - Every 5 minutes
• 0 - Every hour
• 0 0 * - Daily at midnight UTC
• 0 9 1-5 - Weekdays at 9 AM UTC
• 0 0 0 - Weekly (Sundays)
• 0 0 1 - Monthly (1st day)

Operators:

• * - Every value
• */n - Every n units
• , - Multiple values: 0 9,17 * (9 AM and 5 PM)
• - - Range: 0 9-17 * (9 AM through 5 PM)

Testing Locally

Crons only fire automatically in production. Test locally with curl.

Basic test (find PORT from pnpm dev output):

curl "http://localhost:PORT/cdn-cgi/handler/scheduled?cron=0+*+*+*+*"

With custom timestamp (for time-dependent logic):

# Test as if running Jan 1, 2025 midnight UTC
curl "http://localhost:PORT/cdn-cgi/handler/scheduled?cron=0+0+1+*+*&time=1735689600"

Generate timestamps:

date +%s  # Current time
date -d "2025-01-15 12:00:00 UTC" +%s  # Specific date

Test script:

#!/bin/bash
PORT=5173  # Your dev server port

curl "http://localhost:$PORT/cdn-cgi/handler/scheduled?cron=0+*+*+*+*"
curl "http://localhost:$PORT/cdn-cgi/handler/scheduled?cron=0+21+*+*+*"

Example Patterns

Session cleanup (hourly):

"crons": ["0 * * * *"]

case "0 * * * *": {
  const result = await db
    .deleteFrom("sessions")
    .where("expiresAt", "<", new Date().toISOString())
    .executeTakeFirst();
  console.log(`🧹 Cleaned ${result.numDeletedRows} sessions`);
  break;
}

Billing (daily at 2 AM):

"crons": ["0 2 * * *"]

case "0 2 * * *": {
  const subs = await db
    .selectFrom("subscriptions")
    .where("nextBillingDate", "<=", today())
    .selectAll()
    .execute();

  // Queue work instead of processing inline
  await env.BILLING_QUEUE.sendBatch(
    subs.map(s => ({ body: { subscriptionId: s.id } }))
  );
  console.log(`💰 Queued ${subs.length} billing tasks`);
  break;
}

Cleanup old files (monthly):

"crons": ["0 3 1 * *"]  // 1st of month, 3 AM UTC

case "0 3 1 * *": {
  const cutoff = new Date();
  cutoff.setDate(cutoff.getDate() - 30);

  const { objects } = await env.R2_BUCKET.list({ prefix: "temp/" });

  for (const obj of objects) {
    if (obj.uploaded < cutoff) {
      await env.R2_BUCKET.delete(obj.key);
    }
  }
  console.log(`🗑️ Cleaned up old files`);
  break;
}

Best Practices

1. Queue heavy work

// ❌ BAD - might timeout
for (const user of await getAllUsers()) {
  await sendEmail(user);
}

// ✅ GOOD - queue work
const users = await getAllUsers();
await env.EMAIL_QUEUE.sendBatch(users.map((u) => ({ body: { userId: u.id } })));

2. Add error handling

try {
  await task();
} catch (error) {
  console.error('Cron failed:', error);
}

3. Document schedules

"crons": [
  "*/5 * * * *",  // Health checks
  "0 * * * *",    // Session cleanup
  "0 2 * * *"     // Billing
]

4. All times are UTC

'0 17 * * *'; // 5 PM UTC = 12 PM EST = 9 AM PST

Common Mistakes

• ❌ Cron not in wrangler.jsonc
• ❌ Forgetting pnpm generate
• ❌ Long-running work in handler (use queues)
• ❌ Assuming non-UTC timezone
• ❌ No error handling or logging
• ❌ Missing default case in switch

Key Limits

• Minimum interval: 1 minute
• Maximum schedules: 3 (free tier)
• Timezone: UTC only
• Execution: At-least-once (make idempotent)
• Timeout: Same as Worker CPU limits

Workflow

1. Add cron to wrangler.jsonc
2. Run pnpm generate
3. Add case to scheduled handler
4. Test with curl: curl "http://localhost:PORT/cdn-cgi/handler/scheduled?cron=0++++"
5. Deploy and monitor in Cloudflare Dashboard

Architecture

Cron Trigger → Check what needs doing → Queue work → Process in queue consumer

Keep cron handlers lightweight. Use them to schedule work, not process it.