cloudflare-cron-triggers

What this skill does

# Cloudflare Cron Triggers

**Status**: Production Ready ✅
**Last Updated**: 2025-10-23
**Dependencies**: cloudflare-worker-base (for Worker setup)
**Latest Versions**: [email protected], @cloudflare/[email protected]

---

## Quick Start (5 Minutes)

### 1. Add Scheduled Handler to Your Worker

**src/index.ts:**

```typescript
export default {
  async scheduled(
    controller: ScheduledController,
    env: Env,
    ctx: ExecutionContext
  ): Promise<void> {
    console.log('Cron job executed at:', new Date(controller.scheduledTime));
    console.log('Triggered by cron:', controller.cron);

    // Your scheduled task logic here
    await doPeriodicTask(env);
  },
};
```

**Why this matters:**
- Handler must be named exactly `scheduled` (not `scheduledHandler` or `onScheduled`)
- Must be exported in default export object
- Must use ES modules format (not Service Worker format)

### 2. Configure Cron Trigger in Wrangler

**wrangler.jsonc:**

```jsonc
{
  "name": "my-scheduled-worker",
  "main": "src/index.ts",
  "compatibility_date": "2025-10-23",
  "triggers": {
    "crons": [
      "0 * * * *"  // Every hour at minute 0
    ]
  }
}
```

**CRITICAL:**
- Cron expressions use 5 fields: `minute hour day-of-month month day-of-week`
- All times are **UTC only** (no timezone conversion)
- Changes take **up to 15 minutes** to propagate globally

### 3. Test Locally

```bash
# Enable scheduled testing
npx wrangler dev --test-scheduled

# In another terminal, trigger the scheduled handler
curl "http://localhost:8787/__scheduled?cron=0+*+*+*+*"

# View output in wrangler dev terminal
```

**Testing tips:**
- `/__scheduled` endpoint is only available with `--test-scheduled` flag
- Can pass any cron expression in query parameter
- Python Workers use `/cdn-cgi/handler/scheduled` instead

### 4. Deploy

```bash
npm run deploy
# or
npx wrangler deploy
```

**After deployment:**
- Changes may take up to 15 minutes to propagate
- Check dashboard: Workers & Pages > [Your Worker] > **Cron Triggers**
- View past executions in **Logs** tab

---

## Cron Expression Syntax

### Five-Field Format

```
* * * * *
│ │ │ │ │
│ │ │ │ └─── Day of Week (0-6, Sunday=0)
│ │ │ └───── Month (1-12)
│ │ └─────── Day of Month (1-31)
│ └───────── Hour (0-23)
└─────────── Minute (0-59)
```

### Special Characters

| Character | Meaning | Example |
|-----------|---------|---------|
| `*` | Every | `* * * * *` = every minute |
| `,` | List | `0,30 * * * *` = every hour at :00 and :30 |
| `-` | Range | `0 9-17 * * *` = every hour from 9am-5pm |
| `/` | Step | `*/15 * * * *` = every 15 minutes |

### Common Patterns

```bash
# Every minute
* * * * *

# Every 5 minutes
*/5 * * * *

# Every 15 minutes
*/15 * * * *

# Every hour at minute 0
0 * * * *

# Every hour at minute 30
30 * * * *

# Every 6 hours
0 */6 * * *

# Every day at midnight (00:00 UTC)
0 0 * * *

# Every day at noon (12:00 UTC)
0 12 * * *

# Every day at 3:30am UTC
30 3 * * *

# Every Monday at 9am UTC
0 9 * * 1

# Every weekday at 9am UTC
0 9 * * 1-5

# Every Sunday at midnight UTC
0 0 * * 0

# First day of every month at midnight UTC
0 0 1 * *

# Twice a day (6am and 6pm UTC)
0 6,18 * * *

# Every 30 minutes during business hours (9am-5pm UTC, weekdays)
*/30 9-17 * * 1-5
```

**CRITICAL: UTC Timezone Only**
- All cron triggers execute on **UTC time**
- No timezone conversion available
- Convert your local time to UTC manually
- Example: 9am PST = 5pm UTC (next day during DST)

---

## ScheduledController Interface

```typescript
interface ScheduledController {
  readonly cron: string;           // The cron expression that triggered this execution
  readonly type: string;           // Always "scheduled"
  readonly scheduledTime: number;  // Unix timestamp (ms) when scheduled
}
```

### Properties

#### `controller.cron` (string)

The cron expression that triggered this execution.

```typescript
export default {
  async scheduled(controller: ScheduledController, env: Env): Promise<void> {
    console.log(`Triggered by: ${controller.cron}`);
    // Output: "Triggered by: 0 * * * *"
  },
};
```

**Use case:** Differentiate between multiple cron schedules (see Multiple Cron Triggers pattern).

#### `controller.type` (string)

Always returns `"scheduled"` for cron-triggered executions.

```typescript
if (controller.type === 'scheduled') {
  // This is a cron-triggered execution
}
```

#### `controller.scheduledTime` (number)

Unix timestamp (milliseconds since epoch) when this execution was scheduled to run.

```typescript
export default {
  async scheduled(controller: ScheduledController): Promise<void> {
    const scheduledDate = new Date(controller.scheduledTime);
    console.log(`Scheduled for: ${scheduledDate.toISOString()}`);
    // Output: "Scheduled for: 2025-10-23T15:00:00.000Z"
  },
};
```

**Note:** This is the **scheduled** time, not the actual execution time. Due to system load, actual execution may be slightly delayed (usually <1 second).

---

## Execution Context

```typescript
export default {
  async scheduled(
    controller: ScheduledController,
    env: Env,
    ctx: ExecutionContext  // ← Execution context
  ): Promise<void> {
    // Use ctx.waitUntil() for async operations that should complete
    ctx.waitUntil(logToAnalytics(env));
  },
};
```

### `ctx.waitUntil(promise: Promise<any>)`

Extends the execution context to wait for async operations to complete after the handler returns.

**Use cases:**
- Logging to external services
- Analytics tracking
- Cleanup operations
- Non-critical background tasks

```typescript
export default {
  async scheduled(controller: ScheduledController, env: Env, ctx: ExecutionContext): Promise<void> {
    // Critical task - must complete before handler exits
    await processData(env);

    // Non-critical tasks - can complete in background
    ctx.waitUntil(sendMetrics(env));
    ctx.waitUntil(cleanupOldData(env));
    ctx.waitUntil(notifySlack({ message: 'Cron completed' }));
  },
};
```

**Important:** First `waitUntil()` that fails will be reported as the status in dashboard logs.

---

## Integration Patterns

### 1. Standalone Scheduled Worker

**Best for:** Workers that only run on schedule (no HTTP requests)

```typescript
// src/index.ts
interface Env {
  DB: D1Database;
  MY_BUCKET: R2Bucket;
}

export default {
  async scheduled(
    controller: ScheduledController,
    env: Env,
    ctx: ExecutionContext
  ): Promise<void> {
    console.log('Running scheduled maintenance...');

    // Database cleanup
    await env.DB.prepare('DELETE FROM sessions WHERE expires_at < ?')
      .bind(Date.now())
      .run();

    // Generate daily report
    const report = await generateDailyReport(env.DB);

    // Upload to R2
    await env.MY_BUCKET.put(
      `reports/${new Date().toISOString().split('T')[0]}.json`,
      JSON.stringify(report)
    );

    console.log('Maintenance complete');
  },
};
```

---

### 2. Combined with Hono (Fetch + Scheduled)

**Best for:** Workers that handle both HTTP requests and scheduled tasks

```typescript
// src/index.ts
import { Hono } from 'hono';

interface Env {
  DB: D1Database;
}

const app = new Hono<{ Bindings: Env }>();

// Regular HTTP routes
app.get('/', (c) => c.text('Worker is running'));

app.get('/api/stats', async (c) => {
  const stats = await c.env.DB.prepare('SELECT COUNT(*) as count FROM users').first();
  return c.json(stats);
});

// Export both fetch handler and scheduled handler
export default {
  // Handle HTTP requests
  fetch: app.fetch,

  // Handle cron triggers
  async scheduled(
    controller: ScheduledController,
    env: Env,
    ctx: ExecutionContext
  ): Promise<void> {
    console.log('Cron triggered:', controller.cron);

    // Run scheduled task
    await updateCache(env.DB);

    // Log completion
    ctx.waitUntil(logExecution(controller.scheduledTime));
  },
};
```

**Why this pattern:**
- One Worker handles both use cases
- Share environment bindings
- Reduce number of Workers to manage
- Low